HPI Racing - RS4 Pro 3 Bulding Tips

These are building tips that HPI team drivers have found will increase the effectiveness of your Pro 3 kit!

Caster and Kick-Up
Because the Pro 3 includes several parts that allow you to change settings like caster, kick-up, rear toe, Ackerman and other things, racers who are not familiar with these settings need to know what different settings will do to their car.

Caster - The standard setting is 8 degrees. Using the 6 degree blocks will give you more initial turn-in to a corner, but less coming out of the corner as the car shifts its weight to the outside wheels.

Kick-Up - The standard setting is 2 degrees. Using the 0-degree block is best for very smooth and flat tracks and/or when you want more initial turn-in to a corner.

Sway Bars - When to Use Them
Sway bars are used only on high-bite tracks that are smooth and free of bumps and ruts. Carpet racing and permanent asphalt tracks are two examples of a good use of sway bars. If the car is oversteering (too much steering, the rear end comes loose), try the black swaybar in front. If the car is not turning enough, or understeering, try the black swaybar in the rear. Sway bars are a good way to prevent "chattering", or the rear tires skipping on the ground through a corner (a result of too much rear traction, a precursor to traction rolling). Sway bars should not be used on bumpy tracks because they connect the suspension arms together, limiting the effect of the suspension.

How to Tune Your Car
This will be a short lesson in HOW to tune your car, not WHAT to change.

1 - The first thing you must do is figure out what the exact problem is. If you think your car doesn't have enough steering, have a friend watch your car and your driving, then let that friend drive the car. If the friend is a better driver than you, they may tell you there is no problem with the car, the problem may lie with your driving technique.

2 - Remember that whatever you change on your car, you will affect something else in the handling. If you needed more rear traction, you can lengthen the rear shocks to gain it, however you will lose steering. To get the steering back, you can change from 8 degree to 6 degree caster blocks, but you will lose steering coming out of a turn. And on and on.

3 - MAKE ONE CHANGE AT A TIME. This is extremely important, so we'll repeat it: MAKE JUST ONE TUNING CHANGE ON YOUR CAR AT A TIME. If you make even two tuning changes on your car, whether it's gearing, tire choice, shock location, wing mounting, body type, or anything at all, you will NOT know what affected your car, and whether it's better or worse than before. Ideally, you should run your car, have a friend time your laps, make a change, run the car again, see if the times improved, etc. If on an outdoor track, note the time of day and temperature of the track and the effects each change made.

4 - A technique that pro racers use at events where practice time is limited is to go to the extremes when tuning their cars. You will probably find a happy middle ground in between those settings, but you will now know what those settings will do, and hopefully you will know how far you should go when changing the various settings on the car.

5 - Remember that you may not always be able to tell exactly what your changes have done to the car, but if you let your friend drive it in the middle of the practice run (when the tires are warm) they may be able to tell the difference, because you are driving the car constantly.

6 - Finally, remember to RECORD THE CHANGES AND THEIR EFFECTS. If you don't keep track of your changes, you won't know what changes to make in the future.

Rebuild Often
Every 3-4 times you race, or before any large event, you should take apart and rebuild your car to check for any loose items, broken parts, cracked parts, questionable bearings, bent dogbones, etc. Rebuild your shocks, as well, and consider replacing any worn-out tires or cracked wheels with a fresh set of wheels and tires. Check your car body for cracks over the wheelwells, areas where the wheels are rubbing, loose wing mounting screws and other things. Looking over your car every week or two helps you keep track of problem areas that you shoud keep an eye on, and tells you when a part needs to be replaced. Before a large race, you should replace the shock towers, suspension arms and other plastic parts that take a beating every week.

Hot Weather Racing - Use a Fan!
Taking a fan with you to summer races can provide a significant advantage to you and help keep your motor, batteries and charger undamaged. A table-style oscillating fan (up to a foot across) is a powerful way to keep cool personally (so you're more relaxed for racing) and also can be directed to flow cooling air over your charger, power supply, and even your car (with the body off) after racing to cool down your motor and batteries. A more compact option is a 12v DC computer fan that can be connected to your power supply with alligator clips, or a 120v AC computer fan (or whatever voltage your country uses) that plugs into a normal power socket. Use fan guards and screws on computer fan to turn it into a car stand so you can set the car on it after you take a run; the constant flow of air will keep the car cooled off!

Spec Tire Racing Tip
If you are racing at a large event which limits the number of tires of a specific type you can use (or you're just short on cash), the first thing you must do is find the "right" set of inserts. Hopefully the onsite hobby shop will have enough, but you may have to scrounge around to find a set from a racing buddy. Practice with what you are told is the right insert - normally you can run 3-4 times on practice tires before the properties of the tires change from wear and temperature. If you get information from a trusted source that different inserts will work better, try those inserts in one set of practice tires. When qualifying or racing, you will normally get 1-2 "good" runs before you should use a new set. Try not to change inserts in the middle of qualifying, the handling of the car will change dramatically. Remember that an outdoor track will not heat up to maximum temperature until 2-3 PM. Early-morning practice on a cold track will be much different than racing in the heat of the day when the track reaches extremely hot temperatures. Tire choice will also affect the handling of the car - if you run a set of tires with 2 runs on them, they will be very different than tires that are fresh and unused. If you have too much steering when racing, try using a set of "scrubbed" tires in the front: these are tires that have one run on them. Proper tire management with a limited number of tire sets is extremely important - if your tires are handled properly, you will have a definite advantage over racers who do not keep track of their tires!

Hot-Weather Wheel Tip
When racing outdoors on hot tracks, try enlarging the holes in the wheels before mounting the tires and inserts. This helps keep the tires cool and enhances their grip. If you need just a little bit extra rear traction, experiment with slightly larger holes in the rear wheels.

Watch out for Battery Bars
Early testing showed that sharp-edged battery bars may wear away at the servo wires where they rise up out of the battery compartment. Put a dab of Shoe Goo or another silicone-based glue over the wire where it bends over the battery compartment rail to protect the wire from fraying.

Secure your Servo Wire
To make sure your steering servo wire stays in place, use a dab of Shoe Goo or another silicone-based glue on each side of the battery compartment to hold the wire down.

Cushion your Batteries
Use our #6273 Foam Spacer strips to add a cushion strip to the bottom of your battery brace. This keeps the batteries from sliding from side to side when in a series of turns, and you can use the foam in other places on the car, such as the bumper and transponder holder.

Smooth out the Steering
Try this tip from Masayuki Murai for slightly smoother steering: he placed the servo rod ball link on the bottom of the bellcrank arm.

Torque Rod
To lessen front-to-rear flex on the car, try using the holes that are provided in the battery brace to attach a long turnbuckle. Use our long self-lubricating Heavy Duty Ball Ends (#A303, $4 for 8) and a 53mm or 2.5" turnbuckle. This tip is recommended for carpet racers or modified class racers. You don't have to remove the rod to take out the batteries, either - just remove the clip from the front end of the brace, lift the front of the brace and slide out the

Take Notes
If you want to be a "serious racer", you'll keep a notebook or several setup sheets for your car handy to take notes on. Changing conditions at your track means you might have to change your car around to keep up with temperature changes and track conditions. If you have a place to keep notes you can see what worked and what didn't in past situations. Write down things like air temperature and general humidity (from a local newscast or cheap thermometer), track surface temperature (borrow a temp gun from a Nitro racer), plus track conditions like tight or sweeping turns, high grip or loose surface, etc. Also, keep track of what setup was on your car during these conditions and how the car reacted. If you make a change, make one change at a time (moving shock positions, trying different tires, etc.) and write down how the car reacted after the change. Eventually you will build up almost a database of tuning and handling knowledge and be able to accurately predict what will happen to the car in almost any given situation.

Keep your car clean
Spotting problems on your car is much easier if it is kept clean an in good repair. A dirty car covered with scratches and tire dust is hard to see trouble areas, like a cracked upright or a loose screw. Use your track's air compressor hose or visit a wholesale store to pick up compressed air cans. These compressed air cans are great for spot cleaning your car and are much more expensive at electronics and hardware stores.

Use the shock bladders
HPI Factory Team Drivers have found through extensive testing that using the shock bladders from their Pro 2 cars work really well on the Pro 3. Remove the foam shock inserts and use shock bladders instead for a shock that is a little easier to build. The shock bladders are #6814 ($2 per pair) for the standard bladders and #72112 for the firm shock bladders ($4 for 4). The newer firm shock bladders increase the rebound action of each shock for a different driving feel.

"There's lots of flex"
The first thing people will notice on the Pro 3 (apart from the center battery position) is the amount of chassis flex the car has. While a super stiff ladder-frame chassis may work for real cars, we have found that allowing the chassis to flex and act as an active suspension component allows the car to have lots of rear traction. Before letting your friends and fellow racers judge the car, let them test drive it after you have it tuned to your track!

Starting Setup
You will need to adjust your front and rear camber settings to an increased negative angle if you are trying to transfer a setup from the Pro 2 to the Pro 3. You will probably also need to use slightly stiffer springs front and rear, but can probably try the same shock piston/oil combination to start with. Use the same tire/inserts you used to use and the same body. Now test run your car! Make sure to take notes, don't "keep it all in your head", you'll forget what changes made a positive difference.

Carpet Setup
Racers on carpet may see a need to use the holes in the battery strap to attach turnbuckle braces so the car flexes less from front to rear. We have provided mounting holes in the strap, in the motor brace above the rear end of the battery strap and you can also use a second turnbuckle attached to the front of the chassis in the button head screw location that holds the steering brace.

Belt Tension
You probably won't have to tighten the front belt until the car has run in several races. Check the rear belt tension periodically if you race with modified motors, you could be losing lots of acceleration coming out of a corner if the belt is slipping!

Optional Wide Body Mounts
Racers may find an extra advantage by using the optional rear body mount position provided with the Pro 3 kit. The wider body mount position helps stabilize the body when the car is at high speed or in sharp turns. Use #A471-8 and mount it on the outside holes of the rear shock tower. Use the button head screws that hold on the rear body mount "shelf" to attach the mounts. Wider front body mounts can also be mounted, use our #6507, #A371, #A351 parts trees for the extra mounts. #6507 provides one pair of front body mounts, #A371 and #A351 provide two pairs of mounts, as well as the adjustable body mount caps. Remember to use the original body mounts in the stock locations, but cut them just above the front bumper brace. The original mounts help hold the bumper in place.

Check your tires!
Before each race, check the outside edges of each tire for gaps between the tire and wheel. Use thin CA and a wide rubber band wrapped around the tire to close the gap. Doing this will ensure a good bond so that your tires do not come off in a race.