R/C Glossary

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Here is the beginnings of our R/C Glossary. Because there are always new developments and advances coming up in our fast-growing industry, expect changes and additions often! This is just the beginning. Do you have suggestions for our Glossary? Email the webmaster with your suggestions.

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.12 -- Generally, this is the smallest nitro type engine that is available for sedan R/C cars. Many kits come equipped with a .12-size engine. Some .12-size engines are more powerful than many .15-size engines, which indicates they are more efficient, have more tuning capability and/or larger carburetor openings. The ".12" refers to the displacement size of the engine in cubic inches, much like a full-size engine.

.15 -- This is the second-largest generally available nitro type engine that is available for sedan R/C cars. Most ready to run (RTR) car or truck kits come equipped with a .15-size engine. Although the larger displacement would lead you to believe the .15 engines are more powerful, there are some .12-size engines that are more powerful than many .15-size engines, which indicates they are more efficient, have more tuning capability and/or larger carburetor openings. Also worthy of noting is that .15 engines are not allowed in large sanctioned races in some countries, which could mean that a car or truck may not be allowed to participate in an organized race, because many race clubs or tracks follow these rules examples. The ".15" refers to the displacement size of the engine in cubic inches, much like a full-size engine. NOTE: Some .15-size engines are "big block" engines, while most are based on the .12-size engine case. "Big block" engines won't fit in most 1/10 scale cars without modifications.

.21 -- This is the largest generally available nitro type engine that is available for R/C cars. The ".15" refers to the displacement size of the engine in cubic inches, much like a full-size engine.

2 Speed -- See Two Speed

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A Arm -- This generally refers to the lower suspension arm of the car, although it can refer to the upper arm also.  

ABS -- A form of plastic that is easy to form but is not crash-resistant. HPI Racing does not use this type of plastic for any kit parts, however some of our 24mm white wheels are made from ABS, which is slightly lighter than the high-impact nylon used in our other wheels.

Accelerate -- To make the car move faster, either from a full stop or while it's already moving.

Acceleration -- A measure of how quickly a car can accelerate. Affected by items like the  weight of the car and its rotating mass.

Ackerman -- Rudolf Ackerman is a man who worked out a steering system for horse-drawn carts, and we use his name today to describe the angle of the inside tire in relation to the outside tire when the wheels are turned to full "lock"--the farthest the wheels go to the left or right. Normally, when the front wheels are turned all the way left or right, the inside wheel is at a sharper angle than the outside wheel. If you extend the center line of each front tire to a point where the intersect and measure that angle, that is the Ackerman angle. Ideally, for perfect steering, the Ackerman angle will cross at the center line of the rear axle.

In a wide turn, the front tires are not turned very far to the right or left, the inside wheel is not steering at a sharper angle than the outside wheel, and the Ackerman angle is not very wide. In a tight turn, the inside wheel is steering at a steeper angle than the outside wheel, and this is what is called the "Ackerman effect". A bellcrank steering system approximates a way to copy the Ackerman effect, and is adequate for R/C cars because of tire slip, tire sidewall folding and other factors. 

Adjusting the Ackerman angle can be done by changing the length of the center link, also called the Ackerman link that connects the bellcrank steering arms, or changing the mounting location on the steering arms without changing the link length. Most racers won't need to change the Ackerman angle, and actually it is best left to experienced racers who wish to try something new. 

If you wish to learn what changing the Ackerman angle will do, see below:

The Nitro Racer 2, Pro 2 and Pro 3 use bellcrank steering arms that have two sets of mounting holes (inner and outer) for the Ackerman link. The Pro 2 and Nitro Racer 2 kits use the outer holes, while the Pro 3 uses the inner holes on its new bellcranks. Mounting the Ackerman link to the outer holes will result in a small Ackerman angle. Using the inner holes will increase the Ackerman angle.

A smaller Ackerman angle (done by lengthening the Ackerman link or using the outer link holes) will give you more aggressive steering into a corner with a possibility of oversteer at the middle of turn, when the most weight is on the outside tires. The RS4 Pro 2 and Nitro RS4 Racer 2 kits use the outer Ackerman link holes in stock form, so they has more aggressive steering than other cars, everything else (damping, tires, suspension) being equal. 

A larger Ackerman angle (achieved by shortening the Ackerman link or using the inner link holes) will give you more predictable and smoother steering. The new RS4 Pro 3 uses the inner Ackerman link holes, so its steering will be more predictable than the Pro 2. 

Ackerman Link -- The center link of the bellcrank steering system that connects the two steering arms.

Air Dam -- An extension of the front bumper that blocks, or dams, too much air from getting under the car and producing lift. Most R/C bodies for Touring Cars have air dams built in.

Aluminum -- In general terms, aluminum is a metal that is lighter than steel, but not as strong. It can be machined (cut on a machine) to replace many plastic parts of an R/C car, but is not recommended for replacing suspension arms. 

Angle of Attack -- (AOA) Refers to the angle that a surface contacts the air, usually mentioned when talking about spoilers and wings. A higher AOA helps solve oversteer but increases drag and decreases top speed. A lower AOA is used to alleviate understeer and increase top speed.

AM -- Short for Amplitude Modulation, an AM radio in R/C is considered a "budget" radio, what most newcomers to R/C will start out with. Most hobbyists will be fine with an AM radio, but some racers can benefit from FM or PCM radios. An AM radio will have more glitching than these other, more expensive, radios.

Anti-squat -- Refers to the angle of caster on the rear wheels. However, that angle prevents the squatting of the rear suspension, so 'anti-squat' it is. Anti-squat is most effective on acceleration from a stop, when much of the car's weight is forced onto the rear suspension. Lifting the front of the hingepin of the rear arms gives a caster (anti-squat) angle, and helps to transfer the power that makes the car want to do a wheelie into forward motion.

Axle -- What a wheel of a car spins or rotates on. A "drive axle" is an axle that is actually powered and turns the wheel (such as the rear axles on a rear wheel drive car), otherwise the wheel will spin on bushings or bearings on the axle.

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Backmarker -- Any racer that is getting lapped.

Ball Cup -- A hollow plastic piece that snaps onto a ball end that provides a pivot point, usually for suspension movement. Using a ball cup/ball end assembly instead of a rigid system allows the car to absorb crash damage, so the ball cup will "pop off" instead of break. Ball cups are usually paired with turnbuckles for the ultimate in ease of use and assembly.

Ball End -- A metal ball that has a hex (6-sided) and screw threads on one end. A ball cup will attach over the ball end to provide a pivot point 

Batteries -- A battery holds an electrical charge for future use by an electrical device. A single cell is a battery, a collection of cells is a battery pack. Batteries in use in the R/C hobby can contain alkaline materials (non-rechargeable, used for transmitter batteries), nickel-cadmium or nickel metal hydride. Each type of battery has its advantages and disadvantages, see the associated glossary entries for details.

Battery Pack -- A collection of batteries that are joined together to combine the voltage of the batteries to power an electrical device. This term is used for electric R/C cars (normally a pack to power the motor) and also for Nitro cars (to power the servos controlling steering and throttle/brake). 

Bearing -- A hollow metal "donut" that uses balls inside to increase the efficiency of a rotating shaft (like an axle). Highly recommended as the first option part for any kit equipped with bushings, bearings have become a standard accessory in most R/C kits today.

Bellcrank -- The type of steering mechanism most common in R/C cars, trucks and buggies. It consists of two posts, one of which has a connection to the steering servo. This connection turns one of the steering arms, which is connected with an Ackerman link to a second steering arm. The left side steering arm is connected to the left steering knuckle with a turnbuckle, just as the right steering arm is connected to the right steering knuckle. Some bellcrank systems allow racers to alter the Ackerman angle, which can tune the steering effect of the steering system in different ways.

"Big Block" -- In R/C terms, this refers to a .21 engine or a .15 engine that uses a .21 engine case.

Bled -- After correctly assembling a shock absorber with no excess oil and no air bubbles, that shock absorber is considered properly "bled". 

Bleeding -- The process of removing air and excess oil from shock absorbers. A properly assembled shock absorber is considered "bled".

Body -- In R/C terms, the body is the thin, (usually) clear plastic piece that covers the car and provides the "shape" of the car. Most bodies, especially on touring cars and some other vehicles, are easily interchangeable, so it's possible to run a street truck body, then change it for a sedan body, then change that for a coupe body.

Brake -- The system used to slow a car or bring it to a stop. In an electric car, the electronic speed control performs this function. In a nitro car, braking is normally provided by a disc brake and brake pads.

Brake Check -- A driving tactic that is used to disturb a racer's concentration. A car that is being followed closely by another car can abruptly slow down in a section of the track where braking normally doesn't occur, causing the following car and other cars to swerve to avoid the car in front. Sometimes this works, sometimes it doesn't!

Braking -- Usually used in sentences like "under braking" or "need more/less braking", this simply refers to the time when the car is actually using its brakes.

Brake Fade - A term used when a car's brakes heat up and provide less stopping power, forcing the driver to learn to brake earlier as a long race progresses. Upgrading to our Fiber Brake Disk will prevent brake fade for racers. Drilled brake disks look really cool, but we are not aware of any actual performance advantages they may have.

Braking Zone -- The area of a track where cars are slowing down to approach a corner. Easiest to find at the end of a straight section. A track can have many braking zones.

Break-In -- The process of running a nitro powered engine at idle speeds to prepare it for general use. The generally accepted method is to run the engine very rich (the exact needle valve adjustment will vary from engine to engine) for at least 3-4 tanks while the car is on a car stand. Running a fan over the engine and varying the idle speed slightly during break-in is also generally accepted. NOTE: As the engine breaks in, the speeds will pick up and you may have to richen the air/fuel mixture slightly. An engine isn't fully broken-in until it has run about 10-15 tanks, at which point you will see its full potential.

Buggy -- Among the more popular types of R/C cars, buggies are durable cars that can run on most surfaces. The most popular are rear-motor two-wheel drive (2WD) electric buggies, but four-wheel drive (4WD) nitro and electric buggies are popular also.

Bulkhead -- A part of the car that is generally connects to the chassis. During assembly, other parts are connected to the bulkhead, making the bulkhead one of the primary foundation pieces of the car.

Bushing -- A metal "donut" that supports a rotating shaft (like an axle). Most bushings are metal, with most metal bushings made out of something called Bronze Oilite. This is a metal that is permanently lubricated.

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"Calling Traffic" -- Some tracks have a policy of telling racers that are getting lapped that the leader of the race is coming up behind them. The backmarker is expected to move over and not interfere with the leader and any battles for position. However, some tracks do not have this policy and expect backmarkers to move

Camber -- Seen from the front and rear of the car, the angle of the tires in relation to the ground; tires that are perfectly perpendicular to the ground (90 degrees) are said to be at 'zero camber'. If the tops of the tires lean towards each other, the tires have negative camber, and if they lean out, the tires have positive camber. As a general rule, never have positive camber, and make sure the camber of, say, your front right wheel equals the camber of your front left wheel (make the camber angles on each axle match). If we were talking about oval racing, the rules would be different, but we're not. Sedan racing, with it's straights, turns and chicanes requires that, among other things, camber angles match. Usually one degree of negative camber on the fronts is good, because you want a good contact patch throughout a turn, and one or two degrees of negative camber on the rear wheels is fine. From there, experiment, one degree at a time.

Camber Link -- Normally made up of a turnbuckle or threaded rod with a ball cup at each end, this allows the suspension arm and upright to flex a little more than an upper arm would.

Carburetor -- Called "carb" for short. The mechanism on an engine that controls the ratio of fuel and air that enters the engine. There are different types of carburetors:

Barrel Carburetor: the standard model engine carburetor, carried over from airplane engines when they were adapted for car use. For most hobbyists and racers this type of carburetor is fine, because it is simple to install and adjust. The throttle servo turns a "barrel", which has a hole through it, and this controls the amount of air going into the engine. A needle valve on the carburetor controls the amount of fuel going into the engine.

Slide Carburetor: a highly modified, car-specific type of carb that has the barrel of the carb slide along its axis, instead of turning. This provides a quicker response at the expense of a complicated set-up procedure. This type of carb will benefit a small number of racers and is not suggested for casual hobbyists. Two or three needle valves control the fuel intake at different RPM ranges. 

Car Stand -- Simply, this is something a R/C car will be on while work is being done to it. It can be as simple as a block of wood, or as complicated as a padded rotating stand with parts bins. Another main function of a car stand is to keep the wheels off the ground while work is being done.

Caster -- Almost every car has some caster built-in. Caster is the angle that the car's front wheels pivot on when turning. Most on-road Touring Car type kits use between 5 and 10 degrees of caster. Off-road kits like buggies and trucks have about 25 to 30 degrees of 'kick-up' on the front axles. More caster generally gives more steering going into a turn, but less coming out. The opposite is also true: less caster give less steering going into a turn (initial steering), but more steering as you exit. Caster also gives more stability on straightaways, but this effect is more pronounced in 2WD vehicles. 

Cell -- Another term for batteries, but in a singular reference (such as, "look at this cell), this generally refers to the nickel-cadmium or nickel-metal hydride batteries used in R/C cars.

Center of Gravity -- can be shortened to CG or cg. A point in space that represents the central point of a car's mass. If you don't race or are just starting, the only thing you need to know about center of gravity is that if you have a high CG the car or truck will be easier to tip over in tight turns, especially at high speed. As you get more experienced in racing, you will learn to keep everything on the car or truck as low as possible to enhance handling.

Chassis -- The foundation of an R/C car, this is the main portion of the car that everything attaches to. It can be made from woven graphite, molded plastic composites or aluminum. Normally it is flat with lightening holes cut into it but if molded from plastics it can have bent-up sides and other features.

Class -- In radio controlled car racing, the "class" refers to the type of car you have, and what "class" it would race in. In general, there are Touring Car, Mini, 2WD buggies, 2WD trucks, 4WD buggies, Rally, Super-Size, Oval Pan Car, 1/10th scale Pan Car, 1/12th scale Pan Car and a couple of other classes. These classes are further divided by the mode of power, either Electric or Nitro. The most popular classes right now are electric and Nitro Touring Car, and electric 2WD buggy. When deciding what type of kit you want to get for your first R/C kit, try to decide what type of kit and what type of power source you will get, this will narrow your selections down considerably! 

Closed Cell Foam -- A type of foam that is molded, normally used in R/C for molded inner foams. More expensive than open cell foam, it holds its shape better and if molded it does not move back and forth on a wheel.

Clutch Bell -- The equivalent of a pinion gear on a nitro engine, the clutch bell is on the end of the crank shaft and connects with the car's spur gear(s). In a cutaway view, the clutch bell looks like a bell, which is where it gets the name. Inside the hollow part of the clutch bell are the clutch shoes, which will expand with engine RPMs to come in contact with the clutch bell, making it spin. This makes the spur gear turn, and the car moves forward!

Clutch Shoes -- Clutch shoes are attached to the engine flywheel and expand under increasing RPM to contact the clutch bell. The clutch bell spinning makes the spur gear turn, and the car moves forward!

Compound -- When talking about tires, the firmer (harder) the compound, the longer life it will have, but it won't have as much grip as a softer tire would. Most racers use a firm compound tire as the racing surface heats up during the day. A softer compound tire is best used when the track is cool, such as in the morning or late evening. Examples of these compounds include our 20R tires (our softest), 23R, 27R (medium), 33R and 35R (our firmest). 

Contact Patch -- The "footprint" of the car's tire, or the area of the tire that comes in contact with the ground at any given moment. Affected by camber, turning and acceleration. A wider contact patch (from wider wheels) does NOT mean you will automatically get more traction.

Coupe -- In general terms, this refers to a 2-door car. Some R/C touring car body manufacturers, like HPI, offer bodies that represent full-size coupe cars.

Crank Shaft -- A part of a Nitro engine that is rotated by the piston, providing circular motion to the outer part of the crank shaft, which is attached to the flywheel and clutch shoes.  

Crystal -- The part of a radio system that tells the transmitter to emit a particular frequency, and also tells the receiver to look for a particular frequency. Crystals normally are packaged in pairs, because the receiver requires a different crystal than the transmitter. You must use the same frequency crystals in the transmitter and receiver to make the car respond correctly to your commands.

CVD -- An abbreviation for Constant Velocity Drive. "CVD" is a trademark of MIP (Moore's Ideal Products, Inc.). MIP offers their CVD universal dogbones for many R/C kits, and their CVD's are featured as standard equipment on the RS4 Pro 2, Nitro MT Racer and RS4 Pro 3. The main features of the MIP CVD's are their improved efficiency over standard universal dogbones, ability to be rebuilt if an axle or "bone" is bent or damaged and ease of finding replacement parts. The MIP website is www.miponline.com. 

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Damping -- Damping is a highly variable part of car tuning. It's affected by the strength of the shock spring (length and thickness of the wire, plus the number of coils), the size and number of holes in the shock piston, and the viscosity, or weight, of the oil in the shocks. The spring controls how hard the shock compresses, and both the piston and the oil control how quickly the spring pushes the shock to its full length (which can be limited by shock spacers), and so affect the quickness of the shock's return. Stiffer springs need heavier oil and/or smaller-hole pistons to control the speed of the rebound, and bumpy tracks need lighter oil so the shocks, or dampers, can compress and rebound quickly. Softer damping gives more 'stick' on a particular wheel, but makes the car less responsive because the chassis takes longer to reset after a turn, and is also more forgiving to drive. Softer damping also reduces weight transfer at that wheel. Stiffer damping makes handling more responsive, but reduces traction to a particular wheel which can make the car slippery as the chassis snaps back into place after a turn. Stiffer damping also increases weight transfer at that wheel.

Differential -- A system that transfers power equally from a shaft input to shaft outputs. A differential (or "diff") allows the outside wheel of a car going through a corner to travel farther than the inside wheel, preserving corner speed and efficiency. There are two main types used in radio control cars: Ball Differentials or Gear Differentials. Ball differentials should be initially set to the kit specifications: with HPI kits, the diff should be set so that the pulley is not be able to be turned with two flat head screwdrivers or Allen wrenches slid through the outdrive. A different type of differential is the One-Way Diff, which uses expensive one-way bearings to control wheelspin. 

Ball Differential (Ball Diff) -- A differential that uses a series of steel or carbide-steel ball bearings in a circle, pressed between two metal rings, to provide the differential action, allowing one wheel to rotate more than another in a turn. Ball diffs are easier to adjust than gear diffs but are harder to maintain, as they need checking every day of running and are not recommended for Nitro racers. Normally a screw on one side controls the tension between the metal rings, which controls how much the outside wheel in a corner can turn. The looser (to a point) a diff is, the more traction there is at that end of the car. To start tuning your car, set the ball diffs to the same tension at each end, and use the diffs only to fine-tune the car. Do not change the settings of your diffs first.

Gear Differential (Gear Diff) -- A differential that uses a series of gears to provide the differential action, allowing one wheel to rotate more than another in a turn. Gear diffs are harder to adjust than gear diffs but are much easier to maintain, because they must be sealed to keep the grease inside from coming off the gears. Tuning a gear diff can only be accomplished by changing the weight (viscosity) of the grease inside the gear diff case. The looser (to a point) a diff is, the more traction there is at that end of the car. To start tuning your car, set the ball diffs to the same tension at each end, and use the diffs only to fine-tune the car. Do not change the settings of your diffs first.

Dogbone -- A part of the drivetrain that connects the outdrive to the axle. This allows the differential to get its power to the axle and tires of the car.

Double Wishbone -- A type of suspension design that uses two wishbone arms (parallel to the ground and each other - one for the main suspension arm and one for the upper arm) to help maintain a constant tire camber as the suspension is compressed. Most R/C cars have this type of suspension design, because, although it is expensive to have on a full-size car because of cost and space issues, on a miniature car where there is no concern over the space needed for a driver, it is much easier to make. Older R/C cars used different suspension technologies that are no longer in use today (at least in R/C), including swing-arm and trailing arm suspensions.

Downforce -- The effect of air contacting the car body's sloped surfaces. Downforce is created by the air dam, hood, windshield, roof, spoiler(s) and wing(s) of the car. More downforce increases drag and slows the car, but raises the tire temperature, making the car easier to drive. Less downforce raises the top speed by reducing drag. The car should be set up so that it can drive with minimal downforce.

Drag -- In car design, drag is the force of air that slows down the car. The lower the drag of the car (in other words, the more aerodynamically efficient it is), the faster the car can go while using the same amount of power. 

Drag Link -- Another term for Ackerman link

Draft -- In racing terms, draft is the area directly behind a car where the air is disturbed and there is very little wind. A real-world example would be putting your hand outside the window of your car, and moving it behind the side mirror, then out from behind the mirror. Behind the mirror is the draft.

Drafting -- In racing terms, this is the act of following the car in front of you close enough that your car does not have to fight drag. This lessens the load on your engine or motor, and on a long straight section of the track your car and the car in front of you can go faster than another car on its own. In R/C racing, this is very rarely able to be used because of the size of the cars and the maneuverability of the cars, even on an oval track.

Droop -- The measure of shock droop is the amount of uptravel the chassis will have if you weigh the car with its full running gear (servo, batteries, motor, etc.), settle the chassis (press down and release on the chassis), then lift each end until the tires lift off the ground. The total upward movement of the chassis at each end is measured as droop.

Dyno -- An expensive piece of computerized equipment that measures the efficiency of a motor. Can be used to select the right gearing, but the dyno in this function is normally only used by pan car or oval racers. 

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E-Clip -- A small device that holds cylindrical parts like hinge pins in place on the car.

Electric -- This general term usually refers to the power source of the car, meaning it uses a battery pack

Electronic Speed Controller -- An electronic device that takes the power from the battery pack and the signal from the receiver and measures a certain amount of power to the car's motor. Only used in electric R/C cars, boats and planes. 

Engine -- In R/C terms, this is a fuel-powered engine that provides the power for forward motion.

ESC -- an abbreviation for Electronic Speed Controller

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Fade -- see Brake Fade.

Failsafe -- A device that is built into a receiver or that plugs between the receiver and servos that prevents a runaway car in the case of battery failure or loss of signal. Some new servos can be programmed 

Feint -- When coming up on a corner, to make a quick maneuver in the opposite direction to get a better line through the corner.

Final Drive Ratio -- The transmission ratio determined by combining the internal drive ratio and the spur/pinion combination with this formula: 

spur gear tooth count divided by pinion gear tooth count multiplied by the internal drive ratio
or
spur / pinion * internal drive ratio = final drive ratio

If you are trying to match the gearing of another driver who uses a different pitch pinion/spur combination (64 pitch instead of 48 pitch, etc.), or a driver that uses another brand of car, you can use this formula to get a better idea of what to use. Just get the internal drive ratio of the other car and find out the pinion/spur gears that are used, then adjust your gearing to match the final drive ratio of the other car. Remember to account for the motor being used, modified motors vary widely as more or less turns are used, and even stock motors are different from their construction, brush or spring usage, etc.

Fixed Link -- A type of linkage that cannot be adjusted, usually used on ready-to-run cars for camber and steering links. Easily replaced with turnbuckles for experienced racers who with to alter the car's setup.

Flex -- A measure of how much a certain part will bend under varying degrees of pressure or force. Every part will bend or flex, some more than others. 

Flywheel -- The flywheel helps the engine's crank shaft maintain momentum and aids in idling. A heavier flywheel will aid in torque (pulling power and acceleration), while a lighter flywheel will aid in top speed but may cause trouble with engine idling.

FM -- Short for Frequency Modulation, an FM radio in R/C is considered a better radio than the cheaper AM radios because an FM radio will have less glitching than an AM radio. Most hobbyists will be fine with an AM radio, but racers can benefit from FM or PCM radios. 

Foam Donuts -- Literally donut-shaped pieces of foam, these are mounted on wheels so that pan cars and touring cars can use them. Some race tracks are able to use foam tires (such as indoor carpet tracks for electric cars, or very smooth and clean outdoor tracks for nitro cars), but most racers use rubber tires. Foam tires have the advantage that inserts are not needed, they have better grip than rubber tires, they can last longer than rubber tires, and racers can use rollout calculations to figure out their gearing. However, ride height must be adjusted as the foams wear out, and on a 4WD car the wear must be closely monitored to make sure the car does not pull to one side as the car moves.

Foam Inserts -- In the early days of R/C, tires were either foam (for on-road use) or hard rubber (for off-road). The foam donuts did not need inserts, and the off-road tires were hard enough that they could support the weight of the car without collapsing. As tire and car development continued, the tires got softer and required inner foams to make the tire keep its shape on the track. Touring car development followed the same trend as off-road tires: early tires were made of a hard enough rubber that no inner foam was necessary, and eventually tires got soft enough to require them. Most soft compound tires come with a open cell foam insert, while modern sedan racing tires since about early 1999 come with no foams at all, so racers can choose the best molded inner foam for their specific needs. If you do not race, you can use (and re-use, when the tire is worn out) the standard open cell foam insert that comes with your tires. If you do race, you would be well advised to ask around at your local track to find out what tire and insert combination works best! 

Fuel Tubing -- Flexible silicone tubing that provides a way for fuel to get from the fuel tank to the engine carburetor, and air pressure to get from the muffler or tuned pipe to the fuel tank.

Full-Size -- After talking about R/C cars all day, you may want to discuss real cars with your friends - use the term "full-size" to make the distinction!

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Gear -- A general term that normally refers to either the spur gear and pinion gear.

Gearing -- In general terms, this refers to the ratio of the spur gear and pinion gear, when compared to the internal drive ratio of the car. 

Getting Lapped -- A term used when the lead car in a race is passing another car. That car "loses a lap" or "goes a lap down" to the leader. If you are getting lapped, it's usually good form to let the leader get past you in a turn by going wide through the corner. This is even more important if the leader is battling with another car. 

Glitching -- The term that refers to your car losing control temporarily, another term for interference. This happens when the signal from the radio transmitter to the receiver is interrupted for some reason. To solve glitching, make sure you have fresh batteries in your radio, you aren't running near overhead power lines, the antenna on the radio and the car is fully extended, the car antenna isn't in direct contact with carbon fiber or graphite parts (they cause interference), the car antenna isn't cut and the car antenna isn't wrapped around itself. Sometimes twisting the motor wires will help solve glitching. In severe cases, you may have a defective or broken receiver or transmitter. Consider sending either or both to the manufacturers for repair (after talking with their customer service people). In extreme cases you may want to consider replacing your radio gear (get a new FM radio, etc.) or a new receiver.

Groove -- also known as "the racing line", this is the fast way around the track. The quickest way to get around the track is not always a straight line from corner to corner. This term is usually most used in oval racing.

Grooving - no, not dancing! This is a term used to describe the way some tires have a tendency to develop a groove on the inner edge of the tread as they wear. This is less likely to happen to belted tires or tires with firm inserts. Grooving is also a condition that occurs when you have too much negative camber in your car.

H

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Header -- A bent piece of aluminum tubing used on Nitro cars that transfers exhaust gases from the engine case to the tuned pipe or muffler. 

Hinge Pin -- A straight pin of steel or titanium that allows the suspension arms to pivot in one direction. Normally 3mm or 1/8" in diameter, a hinge pin can be any length.

Hit -- Another term for "glitch". 

Hub Carrier -- Also called uprights, these are the parts of the suspension that hold the axles and bearings the wheels of the car turn on.

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Inner Foams -- Another term for insert.

Inserts -- Foam strips or donut-shaped cutouts that support a tire on a wheel. The car can be tuned with inserts, much like full-size race cars are tuned with tire air pressures.

Interference -- see glitching

Internal Drive Ratio -- A measure of the teeth of a car's gears and pulleys. For R/C cars, you divide the number of teeth on the ball or gear diff pulley or gear by the number of teeth on the smaller drive pulleys. As an example, the Pro 2, Sport 2 and Rally cars come standard with 15-tooth pulleys on the gear shaft, and 32-tooth pulleys for the ball diff or gear diff. 32 divided by 15 is 2.16, so the final drive ratio of these kits is 2.16 to 1. The Pro 3 has an internal drive ratio of 2.25 to 1 (36 / 16 = 2.25).

J

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We currently have no definitions in this section of the glossary. Do you have any suggestions? Send them in! 

K

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Kick-Up -- While caster refers to the upward angle at the front wheels of the car, kick-up refers to the upward angle of the front suspension arms. Technically, buggies and off-road trucks have kick-up, not caster, but since they are so similar in description most people use the term "caster".

L

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Lapped -- See getting lapped 

Lean -- A condition referring to engines where the engine is not getting enough fuel. While running lean can help the fuel economy, you run the risk of running the engine too hot and blowing the engine! If your engine runs for a few minutes and shuts off suddenly, it's probably running too lean.

Locknut -- A type of nut that features a nylon insert that helps to "grab" the threads of a shaft or bolt, helping prevent the nut from loosening. Commonly used on axles and other critical areas of R/C cars.

"Loose" -- See Oversteer

M

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mAh -- An abbreviation for milliamp hour, a technical term that shows how long a given power source (like a battery) can give off power. 

Main, or Main Event -- In R/C car racing terms, this refers to the final race of the day in each class you are entered in. See Qualifier, then read the rest of this definition. 

Right after all the qualifying races are over, the race computer will sort all the racers, with the 10 fastest racers in the "A Main", the next 10 fastest in the "B Main", and so on. The number of racers in each main may vary, depending on the number of total racers in the class. Each main event is run in order from the "highest" letter to the "lowest". For example, if there are enough racers to make an E Main, the E Main is run first, then the D, the C, the B, the A, etc. The winner of the A Main is the winner for that class. 

Large events (National and World Championships) will usually have what are called "Triple A Mains". This is only for the top ten racers in each class, and they will all run three main events. In this case, your two best finishes count towards the final score, so if you win two races in the Triple A Main, you would be crowned the champion. 

Mid-Narrow -- see width, wheel

Milliamp -- A rating given to batteries, generally the higher the milliamp rating, the longer the cell can provide power. Currently, batteries are available for R/C use that range from 1500 to 3000 milliamps. 

Mini -- From the Morris Mini Cooper, "Mini" refers to an R/C car that is roughly 1/10 scale but models a very small real-life car like the Mini Cooper or the DaimlerChrysler A-Class. The general difference between a Mini car and a regular sedan car is that the wheels, tires, body, suspension arms and chassis are smaller. For cost-saving measures the rest of the parts are generally interchangeable, especially the drivetrain, bulkheads and shock towers.

Molded Inner Foam -- A form of tire insert that is molded in a special mold instead of cut out of foam sheets. While more expensive, the molded inner foam stays in place on the wheel and does not move side to side as the car goes through cornering forces.

Motor -- In R/C racing this generally refers to an electric motor. 

Muffler -- Installed on every Nitro-powered car, the muffler system traps exhaust gases from the engine case and provide pressure to the fuel tank while keeping noise levels to a minimum. Tuned pipes are another type of exhaust system that provide more power than a muffler.

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Narrow -- see width, wheel or width, chassis

Needle Valve -- An adjustment on an engine's carburetor that allows fuel into the engine. 

Ni-Cad -- The abbreviation for nickel-cadmium

Nickel-Cadmium -- The most common type of battery in use, although it is being phased out of production because of environmental concerns. Easily rechargeable, the R/C hobbyist must be aware that continued charging of this type of battery when it is still partially charged will lead to "cell memory" and decreased runtime and performance. 

Nickel-Metal Hydride -- A type of battery that has no "cell memory", but features slightly less voltage than nickel-cadmium batteries. This means that for racers it is slightly less desirable but for most R/C hobbyists these batteries are better because of less concern for maintenance.

Nitro -- a general term, it could mean many  things. For most people, it refers to the type of car you have: "You have a nitro car?" A car can be "nitro-powered", run on "nitro fuel", and the term can be used for many other things.

Nitro Content -- A measure of the amount of nitromethane that is included in a mixture of nitro fuel. The normal amount of nitro content for fuel is 20% (when used in cars). Racers will use 30% or even 40%, but using a higher nitro content will shorten the life of the engine, which makes the high content fuels more suited for serious racers only. 

Ni-MH -- The abbreviation for nickel-metal hydride

Nylon -- A type of plastic used in many R/C kits. There are many types of nylon:

High-Impact Nylon is able to flex with crash impacts to resist breaking. Most HPI wheels are made from high-impact nylon, as well as many of our suspension arms and shock towers.

Fiber Reinforced Nylon is a plastic that is mixed with fiberglass fibers to produce a stiffer plastic piece. The ratio of fiber to plastic will determine the stiffness of the piece. If it is too stiff, the strength advantage is lost because the piece can break too often. The electric RS4 MT uses a fiber reinforced nylon tub chassis.

Graphite Reinforced Nylon is another type of fiber reinforced nylon, except that instead of fiberglass fibers, the plastic is mixed with graphite fibers, the same type of fibers that make up the graphite mesh in woven graphite pieces. The ratio of graphite fiber to plastic will determine the stiffness of the piece. If it is too stiff, the strength advantage is lost because the piece can break too often. We offer graphite nylon suspension arms for our RS4 Pro 2, electric RS4 MT, Super Nitro RS4 and the Nitro RS4 2/RTR/Racer 2 kits, and the stock shock towers of the RS4 Pro are made of a different type of graphite nylon.

 

O

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Off-Road -- Any type of running surface that is not on a paved surface. Off-Road can mean gravel, loose or hard-packed dirt, grass, etc. Racing classes that run on off-road surfaces include buggies, trucks and usually rally cars.

Offset - see Wheel Offset

One-Way -- A term that refers to either one-way diffs or one-way pulleys.

One-Way Bearing -- A special and expensive type of bearing that will only allow a shaft to turn in one direction.

One-Way Diff -- At some points on a race track, the inside wheels can lift up because of high cornering forces. This causes a normal ball diff or gear diff to "unload". A ball diff prevents diff unloading because it does not allow the tire to spin less than the speed of the belt that turns the pulley. One-way diffs do take getting used to, because you must use very light braking power or none at all. When brakes are applied to a car using one-way diffs only the rear wheels will stop, making the car spin out very easily. Most drivers will need practice to get used to one-ways, but for racers on high-grip surfaces they can be a valuable tuning aid.

One-Way Pulley -- One-way pulleys operate in the same manner as one-way diffs, except the one-way action takes place on a gear shaft instead of the front axle of the car. One-way diffs and pulleys do take getting used to, because you must use very light braking power or none at all. When brakes are applied to a car using one-way pulleys only the rear wheels will stop, making the car spin out very easily. Most drivers will need practice to get used to one-ways, but for racers on high-grip surfaces they can be a valuable tuning aid.

On-Road -- Usually refers to running cars on a paved asphalt or tarmac surface. The term could also refer to a class of cars, such as touring cars, pan cars, etc.

Open Cell Foam -- The less expensive type of inner foam that some tires come with in the package. For general use these are fine, however for racing purposes a molded inner foam works much better.

O-Ring -- A donut-shaped circle of rubber or silicone that seals rotating or sliding shafts, used in areas like shock absorbers and differentials.

Outdrive -- The part of the differential that outputs power to dogbones or universal dogbones.

Oval -- The American-style stock car type of racing, where cars compete on oval tracks of different shapes (true oval, square oval, tri-oval, etc.) and are tuned to only go straight or left. Other types of vehicles not covered in this glossary also compete on ovals, including sprint cars, midgets, motorcycles, snowmobiles, etc. In R/C terms, most oval race cars are pan cars, with all the weight (batteries, electronics, etc.) on the left side so the car is the most stable when turning left.

Oversteer -- (also "loose") Your car's rear end keeps swinging around? Condition: oversteer. The rear tires in an oversteering ('loose') car lose traction before the front wheels, wasting power as the tires slip, looking for something to grip to. You may need stickier (or newer) tires, more rear downforce or there may be other problems. Shock and weight settings may need adjusting too.

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Pan Car -- In R/C terms, this is a car that is made from a flat "pan" of graphite or fiberglass, with an independent front suspension and straight-axle rear "pod". These cars are rear-wheel drive only and use foam tires. R/C Formula 1 cars fall into this category, although the front suspension uses much longer arms and the chassis is narrower. HPI no longer makes pan cars at this time.

Panasonic -- A manufacturer of batteries around the world. Until recently, with the release of their 3000 mAh capacity Ni-MH type cells, they were considered to be behind Sanyo in quality. The recent release of Sanyo's own nickel-metal hydride batteries will be the first direct competition of nearly identical batteries from these manufacturers in over a decade.

PCM -- A type of transmitter and receiver that is even less prone to glitching than FM radio systems. Although more expensive than FM radios, PCM radios were very popular until FM radios got cheaper and almost as glitch-free.

Peak Charger -- The recommended type of charger for nickel-cadmium batteries. Although not recommended for nickel metal-hydride batteries, these chargers can charge these types of batteries, but they must be monitored for temperature (so they don't rise above 110 degrees Fahrenheit) and voltage.

Pinion Gear -- In electric R/C cars, this is the gear that is attached to the car's motor, which in turn spins the spur gear, turning the rest of the drivetrain.

Piston -- An internal part of an internal combustion engine that slides back and forth inside a sleeve. If the piston must be replaced, the sleeve must be replaced also. 

Pitch -- The measure on a pinion gear or spur gear of how many teeth fit per inch. On a 64-pitch gear, 64 teeth will fit within one inch; on a 48-pitch gear, 48 teeth will fit in one inch. HPI offers both 64-pitch and 48-pitch gears for electric cars. HPI Nitro cars use a unique pitch called "one module", abbreviated by "1M" in part descriptions. It is a metric pitch that is ideal for Nitro cars, which run on dirty parking lots. Nitro cars also suffer from engine vibrations, which can loosen. 

Pivot-Ball Suspension -- A type of suspension system brought to scale Touring Cars from 1/8 scale Nitro cars. Instead of the more common lower suspension arm/upper turnbuckle link, the pivot-ball suspension uses inner hinge pins and screws on the outer pivots that adjust camber and track. The caster is adjusted by moving clips on the inner upper hinge pin.

Port -- An opening in the sleeve of a nitro engine. Modifying the port size and shape can affect the power and fuel consumption of an engine, but the modification is best left to a professional.

Porting -- A method of hopefully gaining more power from a nitro engine. If done correctly, you can get more power. If not done correctly, you will have possibly more power but much worse fuel consumption. If done very badly, the engine will not run at all! 

Pullstarter -- A mechanism that allows the starting of a Nitro car engine without the need for a separate engine starter box. Because it is permanently attached to the engine, the engine must sit higher in the car, which affects its center of gravity. It also can affect the rotating weight of the engine itself, however this and the center of gravity affect will not concern anyone but the most serious racer.

Punch -- In R/C terms, this means the same thing as acceleration. Driving "full punch" means you are on the throttle all the time!

"Push" -- See Understeer

Pole Position -- A start position for a race where a car is in the very front of the starting grid. Usually the most desirable position to start from, because other cars must pass you to be in the lead.

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Qualifier -- When you attend an R/C car race, you will normally have two or three qualification races, then you will race in your Main Event. The way racers are sorted varies between different events, but usually you will have your best "qualifying time" determine what Main you will race in (some racing organizations use FTD, or Fastest Time of the Day, to determine qualifying order). The qualifying time refers to the number of laps you are able to complete during the qualifying race (each qualifier is normally 4 or 5 minutes). If you tie with someone else who has the same number of laps, the lowest elapsed time will win. See the entry for Main Event to see how the rest of a race event is run.

R

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Race Director -- The person running and organizing the race. Responsible for calling the drivers to the stand, making sure each car is in the correct spot on the starting grid, calling traffic if necessary, and other duties. 

Racing Line -- the fastest way around the track. Not always a straight line from corner to corner, the racing line is often flowing and smooth, representing feints into hard corners and drifts coming out of corners.

Radio -- 

Radio-Controlled -- Refers to 

Rally -- A newer class of R/C cars, popularized by the HPI RS4 Rally. At first glance appearing to be a touring car with treaded tires, a "true" rally car will feature slightly longer shocks and some protection for the drivetrain. A rally car is generally able to travel on any on-road surface, as well as gravel and hard-packed or loose dirt.

R/C -- An abbreviation of radio-controlled

Ready To Run -- A term that usually means a kit is at least 95% assembled, with minor finishing work being the only requirements to getting it ready. Some painting, tire mounting and minor assembly (such as attaching body posts and body clips) may be necessary, and a nitro-powered car will require break-in.

Receiver -- The electronic device that receives the radio transmissions from the radio transmitter. Through wire plugs inserted into the receiver case, the receiver passes signals to the steering servo and electronic speed control or throttle servo.

Receiver Cover -- A plastic or vinyl cover that protects the receiver from fuel, water, mud, dust and dirt. 

Receiver Pack -- The battery pack that provides power to both the steering and throttle servos in a Nitro car.

Rich -- A condition referring to engines where the engine is getting too much fuel. If you accelerate from a stop and the engine dies, you are probably running too rich and should lean out the engine's low speed idle adjustment a little (by turning the needle valve or low-end adjustment slightly clockwise).

Ride Height -- The space between the lowest part of the chassis and the ground, measured with all of the car's electronics installed; racers measure the front and the rear ride heights separately. Adjustable on the RS4 kits by the shock spacers provided with the kit. There should be enough ride height so that the suspension can be engaged enough to soak up whatever bumps and dips occur on the track, but the chassis should be low enough to the ground so there isn't too much chassis roll (related to shock settings).

Rollcenter -- An imaginary point at the front and rear of the car where the chassis rotates around. Affected by the position of the uprights and rotation points of the suspension arm and upper links, the rollcenter can be changed on an R/C car by adding spacers underneath the rear bulkhead, moving the uprights up or down in relation to the arm, and other methods. 

RPM -- Rotations Per Minute. How many times an engine, motor, wheel, gear, etc., will turn in a minute. In R/C racing this is most important for electric motors and nitro engines.

Rod End -- Similar to a ball cup/ball end combination, except that a rod end is a plastic "eye" that holds a metal or plastic pivot. A screw goes through the pivot and is secured in a bulkhead, suspension arm or other area. 

Rotating Mass -- Refers to the weight of the rotating parts in any car. For an R/C car, this includes the diffs, wheels, universal dogbones, belts, pulleys, flywheels, crankshafts, spur gears and spur gear hubs. The lighter you can make these parts, the faster the car will accelerate and brake, because less force  is needed to get these parts moving. Most people agree that reducing one unit of weight (ounce, gram) equals saving between three to four units of weight that does not rotate. 

RTR -- A term standing for "Ready To Run"

Runtime -- A term that means how long an R/C kit will run or last on one battery pack or fuel tank.

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Sanyo -- A manufacturer of batteries around the world. Long considered the "top" manufacturer, since the days of the 1700 mAh type cells. They have recently released the RC3000H Ni-MH cells, which compete directly with the Panasonic 3000 Ni-MH cells.

Scale -- For R/C hobbyists, this refers to the general size of the car. Many companies offer radio control cars in several different sizes: 1/18, 1/12, 1/10, 1/8, 1/5 and 1/4 scale. The smaller the number after the "1", the larger the actual scale car is. For example, a 1/18 scale car is about 9 inches (23cm) long, while a 1/5 scale car can be up to 36 inches (91cm) long! Most cars are of the 1/10 scale size (because the cost of manufacture and ownership is balanced to the controllability of the car), but there are many types of kits that fall under this size label: Buggy, Truck, Monster Truck, Touring Car and more.

Sedan -- In general terms, this refers to a 4-door car that has a separate trunk. In R/C terms, this refers to a car that is generally 1/10 scale in size, and is the most popular form of on-road R/C racing in the world right now. These kits started out modeling the cars that formed the DTM racing league in Germany in the early 1990's, but (because of interchangeable bodies) now can represent anything from the latest LeMans racer, to street trucks, to the newest cruiser on the road. 

Servo -- A small box full of motorized gears that turns the steering and/or throttle linkage in an R/C car. Available in a range of strengths and speeds, with the faster/more powerful servos more expensive than slower/weaker servos. "Stock servos" usually cost about $12-15 (US dollars) and are the standard servos that are included with most radio sets. These servos are fine to get a kit running, but in the future you may want to upgrade to stronger servos, especially for racing or for the steering of a large-tire off-road kit like our Nitro RS4 MT.

Shell -- Another term for a car body.

Side Plates -- The sides of a wing, they help direct air over the wing and help in stability. Larger side plates help in stability on a long straight section but can affect the turning ability. Smaller side plates aid in turning but don't provide as much straight-line stability.

Side Skirt -- The part of the body panel that is under the door. This term usually refers to an extension of this panel that lowers the effective 'body ride height'. Helps keep air from getting underneath the car, and helps channel air underneath the car from the front to the rear, increasing downforce.

Shock Oil -- A petroleum- or silicon-based oil that is available in different degrees of thickness, used to fine-tune the damping of a shock absorber. As the shock shaft travels up and down, the piston moves up and down also, so the oil must flow through the holes in the piston. The smaller the holes are in the piston, the slower the piston is able to move, and with larger holes the piston is able to move faster. When you are starting out racing and you want to try adjusting your shock settings, you should try changing your springs first, then your piston/shock oil combination.  

Shock -- See Damping

Shock Absorber -- The complete assembly of a shock damper that includes the shock body, cap, spring, shaft and connectors.

Shock Angle -- Move the upper end of the shocks up, and you should get more bite, or grip, at that end. Lay the shocks further down, and you will loosen that end of the car. 

Shock Bladder -- HPI touring car shocks use a shock bladder to assist in bleeding the shocks properly, and to make sure the 

Shock Body -- The wide cylindrical part of a shock absorber that contains the shock oil, shock piston and o-rings, topped by the shock cap and sometimes a shock bladder.

Shock Cap -- Usually a threaded top (or bottom, on some shocks) that closes the shock body and keeps the shock oil inside. Usually sealed with an o-ring, some shocks use a shock bladder to help keep the oil pressure inside at a constant level.

Shock Shaft -- The long metal rod that sticks out of the shock body, usually with a pivot piece on the end that mounts to a suspension arm. The other end (inside the shock body) has a shock piston on it.

Shock Spring -- The coil spring that usually surrounds the shock body of an oil-filled shock. Some shocks consist of just the spring (like a pan car front shock).

Shock Travel -- This does not refer to shock spacers that clip to the shock body, compressing the spring. There are two ways to limit shock travel: Spacers inside the shock, under the piston on the shock shaft or an o-ring or two on the outside of the shock body, on the shock shaft above the spring retainer. The inside spacers limit how far down the shock can extend, and the more you have, the shorter the shock gets at its full length, but you may have to change your ride height. The outside spacers (be sure to use old o-rings!) remove shock travel without compromising the shock length or ride height, so the shock can still deal with dips in the track, but stroke is lessened.

Silicone -- A type of synthetic rubber that is heat-resistant and more durable than standard or natural rubber.

Sleeve -- Refers to an internal part of a nitro engine, which the engine's piston slides up and down in. If the engine's sleeve is replaced, the piston must also be replaced and the engine broken in. Sleeves in 2-stroke R/C car engines are either nickel-plated or chrome-plated. Nickel plating offers cheaper parts but it can wear out faster. Chrome plating is more expensive but worth it for racing.

Slipper -- A short term for the slipper clutch

Slipper Clutch -- A traction control device that uses metal plates and a fiber pad that controls how much power is transmitter from the drive gears of an R/C car to the rest of the drive train. Used mainly on off-road kits.

Speed Controller -- Another name for electronic speed controller

Speedo -- Another name for electronic speed controller

Spoiler -- An angle on the rear of a car that is built into the body lines of the car, or bolted on. No space exists between the spoiler and the bodywork. Examples include stock car bodies and some HPI bodies like the Mazda Miata and Peugeot 406 Coupé. A front spoiler is technically an air dam. The angle that the spoiler contacts the air is the 'angle of attack'.

Spring Rate -- This basically refers to the stiffness of a set of springs. If you want more traction at one end, put on a softer set of springs. If you want less traction, harder springs. If you are bottoming out or the track is really bumpy and the soft springs can't extend fast enough to make the tires contact the surface, put on stiffer springs. If you change the spring rate by a large margin, you'll probably have to switch out the oil or pistons too.

Spur Gear -- The large (usually plastic) gear that a pinion gear or clutchbell turns to provide power to a car or truck drivetrain. Available in different pitches. Many newcomers to the R/C hobby will ask about metal spur gears to prevent gear stripping, however it is usually gear mesh that determines if the gear strips out or not.

Standard Narrow -- see width, wheel

Starting Grid -- The order the cars are lined up at the start of a race. Most races are started with "Le Mans Starts", meaning the cars start from a dead stop. 

Straightaway -- Normally refers to the longest, straightest part of a race track. If there is any place to go full throttle, this is it! 

Steel -- Not used very often throughout a modern R/C kit, steel is a strong yet heavy metal that is still used in some critical parts of today's R/C kit. Typical places you can find steel on an R/C car: pinion gears, turnbuckles or threaded rods, axles, dogbones, ball ends, screws and lock nuts.

Steering Arm -- Parts of a bellcrank steering system that are connected with a central Ackerman link and connect to the steering knuckles with turnbuckles or fixed links. 

Steering Block -- see steering knuckle

Steering Knuckle -- Generally, this refers to the of the car's front suspension that steers the wheels. The steering turnbuckles connect the steering arms and steering knuckles. The front axle will be connected to or pass through the knuckle. If the car is four-wheel drive, the steering knuckle will have two bearings or bushings that support the front axle. Sometimes the steering knuckle can be referred to as front uprights, front hub carriers, or steering blocks.

Steering Link -- The turnbuckle or fixed link that connects the steering arms in a bellcrank steering system to the steering knuckle. 

Steering Servo -- The servo that controls the direction of the front wheels of a car. 

Straight Axle -- Another name for pan cars, so called because of the axle that goes all the way across the rear end of the car.

Stroke -- How far the shock absorber can compress. Can be limited by clips or o-rings on the shock shaft.

Super Narrow -- see width, wheel

Super-Size -- A class of cars that feature larger bodies, tires, chassis and suspension arms to have a larger car overall. Easier to drive because of their larger size, the Super-Size class is really taking off! See our Super Nitro RS4 kit for a great example.

Super Touring -- Another name for sedan racing or touring car racing.

Suspension Arm -- A part of the car to which the uprights, hub carriers, shocks and/or steering knuckles are attached. It will swing up and down as it is absorbing bumps or lowering into dips. It is usually in the shape of a capital "A", which is where the name "A Arm" comes from.

Sway Bar -- Bars that attach to the suspension arms at either or both the front or rear end to limit wheel travel and take away some traction. Normally used only for fine-tuning the car. Not recommended for bumpy tracks. Use a thin bar at first to experiment, then try thicker bars.

T

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Threaded Rod -- A type of connecting rod that has threads facing the same direction. As opposed to a turnbuckle, a threaded rod is harder to adjust because one or both ends must be detached to make an adjustment. Also, the threaded rod forces large adjustments to be made because of the nature of the threads. A turnbuckle can be adjusted in small or large amounts.

Throttle -- Usually refers to the act of accelerating.

Throttle Servo -- A servo that controls the linkage that connects to the engine carburetor of a Nitro car. This same servo also connects to the brake. 

Titanium -- An extremely strong metal, titanium is a rare metal that is stronger than steel yet can be as light as aluminum. Various alloy mixtures of titanium exist, with the strongest alloys featuring the same weight as aircraft aluminum but a much higher rigidity.

Toe Angle -- Refers to the direction the tires face when steering is straight ahead and the car is seen from above. Applies to both the front and rear. Usually, most drivers use one or two degrees of toe-in on their car's front wheels (fully adjustable by turnbuckles on race kits). Most kits come with two or three degrees of toe-in standard on the rear wheels (adjustable by the lower suspension mount or hub carriers on some cars). Slight toe-in (one or two degrees) at either end helps to stabilize the car, but too much (three or more degrees) scrubs off speed, offsetting the benefit of stability. Toe-out on the front end will give increased steering, useful for quick turn-ins, but sacrificing cornering speed and straight-line stability. Toe-out at the rear gives twitchy handling, and it's definitely not recommended. Nearly all R/C kits have rear toe-in.

Top Qualifier -- After each  round of racing, the person with the fastest time in each class is said to be the "top qualifier", meaning they sit on the pole position for the start of the main event. Usually good only for bragging rights, because once the race starts all bets are off, as anything can happen in the main event. Note that top qualifier refers only to the fastest qualifier in the class, the person starting in first place for the B Main is NOT the top qualifier, just the 11th fastest driver.

Touring Car -- In R/C racing, a Touring Car is a 1/10 scale version of a normal street car that has been converted to a race car. Most R/C Touring Cars are four-wheel drive (4WD), meaning all four wheels drive the car. This makes the car easier to drive for most people. 

TQ -- see Top Qualifier

Track Width -- The width of the car, measured from the center of the front axis wheels and the rear axis wheels. A wider stance is more stable and gives better cornering, but with a wider frontal area the car experiences more drag, slowing it down on long straights. See wheel offset for an additional explanation of different offset wheels, and how to use them to get a wide stance with a narrow setup and body.

Transmitter -- The part of the radio system that sends signals to the receiver in the car. Separated into two general categories: stick, which uses two sticks to control movement; and wheel or pistol grip, which has one hand hold the radio with the index finger to control throttle and brake and the other hand control a small steering wheel. Transmitters are also divided into categories by complexity: AM radios are usually cheaper because the parts are cheaper to make, while FM radios are available in simple dial- and potentiometer-controlled versions or digital versions, or "digital/computer radios".

Transponder -- A small radio transmitter that fits in the car to help race directors count laps during races. Many permanent tracks use transponders at their facilities. Most tracks that are starting out cannot afford the high cost of a transponder setup, so they will use a computer keyboard and fast finger-punching to record lap times. 

Tuned Pipe -- A highly modified muffler that substantially increases the power from a Nitro car's engine. 

Turnbuckle -- Similar to a threaded rod, except that the screw threads face opposite directions so adjustments can be made without removing the rod.

Turn Marshal -- At R/C racing events, drivers must turn marshal after their race, meaning they must turn over cars that have flipped, and return cars to the racing surface if they have crashed.

Tweak -- A condition at the front or rear of the car where one tire has more load on it than the other. For example, if the right rear tire has more weight on it than the left rear tire, the car is said to be "tweaked". This can make the car behave unpredictably, including spinning out in turns, turning more in one direction than the other, upsetting the steering trim, and many other problems.

To check tweak (you should check between each race): 
A) Hobby Knife Method: Set the car on a flat, level surface. Using a hobby knife, lift one end of the car at the center point. Watch closely which tire lifts off the surface first. If both tires lift off at the same time, that end of the car is not tweaked. If one tire lifts off before the other, adjust the tweak (see below), turn the car around and check the other end. Adjusting the tweak using the "hobby knife method" must be done by adjusting shock length. An easier way to adjust tweak is with a device like the MIP Tweak Station (see below).

B) Tweak Device Method: You can also use a device like the MIP Tweak Station to check the tweak. Devices like this set one end of the car level, and puts the other end of the car on a pivoting surface. This lets the device show the tweak at either end of the car, without being affected by the opposite end. If the bubble is level, the car is not tweaked at that end. If the bubble is not level, that end of the car is tweaked. Adjust the tweak (see below), turn the car around and check the other end. Adjusting the tweak using this type of device requires adjusting the shock preload using threaded shock bodies or ride height clips. NOTE: before using a tweak device, use the adjustable legs to make sure the device is completely level, and set the shock preloads to the same amounts left and right at each end of your car.

To adjust tweak: 
a) Using the Hobby Knife Method above, if a tire lifts off the ground first, you must lengthen the shock shaft that attaches to that tire's suspension arm. This requires removing the whole shock from the car, taking off the spring perch and spring, holding the shaft with a pair of needle nose pliers, and turning the shock shaft end so it makes the shaft longer.

b) Using a "tweak device", if the bubble is to one side of the level, add more preload to the same side (by adding ride height clips or turning the threaded shock collar towards the bottom of the shock) until the bubble is level. 

Two Speed -- A clutch and gear system that can be installed on most Nitro cars that increases top speed substantially. In general terms, when the first gear ratio has the engine reach a certain RPM range, the second gear is engaged and the car is then accelerated using the second gear ratio. 

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Underbody -- On a real car, a smooth underbody makes the drag of the car much lower at high speeds. In R/C racing you don't need to worry about this, because a totally smooth underbody means that no cooling air gets to the electronics or engine. The RS4 Rally comes with an underbody to help keep dirt and rocks away from the drive train. The RS4 Pro 2 now has an optional underbody for racers in wet or dirty areas. 

Understeer -- (also called "push") When your car just doesn't seem to be turning as sharp as it should, or it can't stay in the low groove and keeps drifting to the outside of sweeper turns, your car is experiencing push, or understeer. The front wheels of a car that is understeering don't have enough grip, so when you try to steer, the car may continue to go straight ahead, or just seem to not turn as much as it should. Easy solutions include slowing down or adding downforce, but more severe problems may need tire, shock or weight adjustments.

Universal Dogbone -- A driveshaft that combines the conventional dogbone and axle into one unit, providing more efficiency and power transfer.

"Unloading" -- At some points on a race track, the inside wheels can lift up because of high cornering forces. This causes a normal ball diff or gear diff to transfer all the available power to the wheel that is in the air. (For an example of this, pull the throttle gently on your car while holding one tire - all the power at that end of the car will go to the opposite, free, wheel.) This is because the differential will put any power at the wheel that is the easiest to turn. This is called diff "unloading". To counter this, racers sometimes use one-way diffs, which allow the tires connected to the one-way diff to continue providing power the wheel on the ground, even if a wheel on the same axle is in the air.

Upper Arm -- Similar to a camber link, except that instead of a turnbuckle with ball ends at each end, the upper arm features a wider hinge area on the inner link, using a hinge pin to pivot on. The outer link usually uses a single attachment point, normally a rod end or pivot ball.

Upright -- Another term for hub carriers.

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Wheel -- Tires are mounted on wheels for stability and precision. Wheels come in several different widths to fit tires of different widths. 

Wheelbase -- The distance between the front and rear axles of a car. A longer wheelbase gives a bit more stability, but a shorter wheelbase gives quicker turning and better acceleration, because the weight of the car is closer to the wheels (in relation to the long axis). All HPI sedan cars have the same wheelbase, while the Super Nitro RS4 has the ability to change its wheelbase with about 20 minutes of work.

Wheel Offset -- This is in relation to track width, but refers specifically to the wheels of the car. The more offset a pair of wheels has, the wider the track and overall width of the car will be. Most HPI sedan wheels are 0mm offset, meaning the edge of the wheel hub that comes in contact with the axle hex adapter is exactly in the middle of the wheel. Some of our sedan wheels (like the 3mm Offset Mesh and Super Star wheels) feature an offset of 3mm, which widens the car a total of 6mm.

Wheel Spin -- Occurs when a tire loses grip, either during acceleration (normally because of too much applied throttle), or through a turn (normally because of a high side load on the tires.

Wide -- see width, wheel or width, chassis

Width, Chassis -- when referring to bodies or chassis designs, we often hear about "width". This is measured from the outside edges of the wheels, front and rear. Most hobbyists will at some point worry about fitting a narrow body on a wide car, or a wide body on a narrow car. At this time, most electric sedans are 180mm to 190mm wide, and most Nitro sedans are 195mm to 200mm wide. Because of the extreme popularity of Nitro sedans, many newcomers to R/C want to know if they can fit narrow bodies on their car, bodies that aren't yet available in wide sizes. Sometimes there isn't a problem with fitting, but this will vary from body to body. Most narrow bodies on wide cars will have some wheel rubbing.

Width, Wheel -- another area where the term "width" is used. Many tires and wheels are 26mm wide, this is considered "standard narrow" or "narrow" width. Early in the history of touring cars, some companies (HPI included) offered 31mm tires and wheels, called "wide" since they are the widest ever offered for touring cars. A few years ago, some companies offered 22mm "super narrow" tires and wheels for less rotating mass. These were never legalized for sanctioned racing, and worldwide rules organizations kept the tires between 24mm and 26mm, so the most recent development in tires has been the 24mm "mid-narrow" tire and wheel, which is a great compromise between the light weight of the super narrow wheels and the contact patch of the narrow tires. See our Tires and Wheels sections.

Wing -- As opposed to a spoiler, which has no space between the car body and spoiler itself, the wing is raised off the mounting surface using posts of some sort. Most wings have upright 'rudder' supports, or side plates, which help stabilize the car in the straights. To help tune your car: A track with many turns and short straights will need small side plates, which won't interfere with turning too much but still give you stability in the straight. A track with many straightaways or two or more long straights could use larger side plates for more straight-line stability. See angle of attack for an explanation of how to use a wing.

Wishbone -- An older name for a suspension arm. Suspension arms used to be shaped like wishbone from a chicken or other bird. Cars using a pivot-ball suspension (like the HPI Proceed) still use wishbone-shaped suspension arms because of the design requirements. Also used to refer to a double wishbone suspension.

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Zip Tie -- The common name for a nylon tie wrap, named "zip" tie because of the sound it makes as you tighten the strap.