HPI Racing - RS4 Pro 3

Here are some production sample pictures of the Pro 3! The car is available now and in hobby shops, waiting for expert-level racers to try!



Prototype testing pictures from Japan!

See the Pro 3 Movie! One lap around Twin Ring Honguu Circuit Note: You will need the Quicktime player to view this movie

How do you improve on one of the fastest touring cars in the world, the HPI Pro 2? You take world-class race experience and combine it with the latest in CAD design. The RS4 Pro 3 is loaded with features that set new class standards.

Our designers gave the RS4 Pro 3 all-new suspension geometry thatdelivers improved handling, with simple set-up options. The central battery mounting position and near-perfect weight distribution gives the RS4 Pro 3 a smooth transition between on and off throttle steering. The all-new layout delivers higher corner speeds & fast changes of direction.

The all-new composite chassis keeps the suspension geometry exactly asour designers intended, ensuring the purest driving feel & clear feedback from the subtlest of set-up changes. Reduced radio interference, improved dampening, reduced parts count and lower price are additional benefits of the composite chassis.

Lightweight composite, true bore, super low friction threaded shocks maximize wheel control under all conditions. They also lower overall car weight & center of gravity significantly. Graphite composite diffs and new short CVD's are standard, providing a significant reduction in rotating mass over the Pro 2. Faster throttle response and improved efficiency are the welcome benefits.

Everywhere you look on the car there have been many technological advances tobring you the best performance and value in the electric competition touring car class.

Retail price for the RS4 Pro 3 is $359.00 (the RS4 Pro 2 was $399.00). Expected street price for the RS4 Pro 3 (#178) in the USA will be around $200.

Check out the many features of the RS4 Pro 3 touring car!

Handling

The most obvious new feature of the Pro 3 is that the batteries run down the center of the chassis, instead of across the chassis as in previous designs. This center-mass design helps make the car nimble and quick, allowing it to transition faster through chicanes and S-curves. Conventional battery/motor designs force the car to transfer more weight in each turn, which makes the car take longer to react to further steering input. Extra-long suspension arms soak up bumps and dips in the racing surface, providing more control and precision over short-arm designs.

Pro 2 owners have been asking for more tuning options, and with a ground-up redesign we are able to comply! We've responded with more camber link positions, optional roll center locations, extra options for kick-up, anti-squat, rear toe-in, front caster, and a dozen different positions for the upper camber links.

With the new weight distribution, the handling duties of the car can now be given over to the shocks, because the new center mass design allows you to use softer shock springs front and rear, giving the car more mechanical grip to use in turns.

Centered battery and motor positioning:
- provides quicker maneuvering through turns and bumps
- makes the Pro 3 more responsive and nimble
- more stable front to rear than conventional designs

Easily adjustable roll center, front caster, front kick-up, rear anti-squat, front and rear toe-in

Extra suspension tuning options front and rear:
- 12 separate upper link locations front and rear (4 inner, 3 outer)
- 2 lower hinge pin locations for front and rear uprights for altering roll center

Lowered front hinge pin location for improved steering

Extra-long suspension arms improve stability while cornering

Full set of turnbuckles with turnbuckle wrench for adjusting front toe and front/rear camber

Shock absorbers

New shock absorbers make their debut on the Pro 3, and have a host of requested features. The most obvious new feature are the threaded composite bodies. Threaded shock bodies are a major new item, and eliminate the need for tweak screws and ride height clips. To adjust the ride height, all you need to do now is screw the aluminum knurled collars up or down! No more searching for the correct thickness clip, and they won't pop off in a bad crash!

The composite shock bodies themselves are also a major feature. With the PTFE shock pistons running up and down inside the shock body, the plastic-on-plastic friction is actually LESS than with aluminum shock bodies, making the shock action more efficient and true. Stainless steel shock shafts are still standard, and hold up in the worst crashes.

Another major feature of the shocks is the new assembly, which now does not require a snap-on type attachment. Previously, the shock bottom cap could get worn out and need replacement after several rebuilds. We've come up with a new twist-on design that slides on then turns, locking the silicone o-rings into place and keeping the included silicon shock oil in the shock body, where it belongs.

Finally, our shock absorbers now use a foam insert to compensate for oil volume changes as the shock compresses and rebounds. We call it our VVS, or Variable Volume System for short, and is extremely simple to use and assembly. No more lost or torn shock bladders!

For tuning purposes, a complete set of our PTFE shock pistons (with five different hole sizes) are included, and the front and rear of the car feature six different shock mount positions. The front shock tower has two mounting positions, with two on the suspension arms and one on the hub carrier. The rear shock tower has three mounting positions, with two on the suspension arms.

Threaded composite shock bodies with knurled aluminum adjustment collars

Easy-to-adjust ride height and tweak with threaded shock bodies

Quick-disassemble bottom end for fast rebuilds

VVS Variable Volume System compensates for oil volume variations during shock compression and rebound

Complete set of PTFE shock pistons included

Silicone o-rings last longer between rebuilds

Stainless steel shock shafts for increased strength

Six separate shock absorber positions front and rear

Chassis

Overall, the Pro 3 is a completely new design, designed and built from the ground up to be a truly worthy competitor in the hotly contested electric Touring Car wars around the world. Its computer-optimized chassis uses fiber-reinforced nylon composites for strength and rigidity, while the chassis' innovative features make it friendly to experienced and beginning racers. Throughout the car, steel Philips screws are used so that anyone can work on the Pro 3 easily and effectively. Our titanium hex screws can be used to reinforce critical areas such as bulkheads and the front bumper, while our aluminum hex screws are useful in areas which are subjected to less stress.

Battery access has been improved, requiring just one body clip to hold in a stick, saddle or side-by-side pack. No tape, no hook and loop straps, no fuss! Simply put the pack in the place, slide the rear of the battery holder under the center bulkhead and clip the front end down.

Electronics access was always a concern with the Pro 2, and now has been completely solved on the Pro 3 chassis. Every component is now easy to get to and replace if needed. The electronic speed control mounts next to the motor for shorter wire lengths and increased efficiency. The receiver mounts forward of the speed control for less electrical noise or interference from the motor. The servo mounts on the opposite site and connects to an all-new bellcrank steering system with new heavy duty HPI ball ends. The transponder can be mounted in several places; we will provide a mount next to the servo or racers can use the front bumper mount for extra steering.

A major feature of all HPI Touring Cars is amazing durability. We have not overlooked this all-important feature when engineering the Pro 3. All of the car's stainless steel hinge pins are held in place using "tuning blocks" that hold the hinge pins at specific angles to set the front kick-up, rear anti-squat and rear toe-in. Should a lower arm or hinge pin need to be replaced, a few screws are all it takes to remove the blocks at either end that hold the hinge pins.

With the majority of the chassis weight down the center of the car, we are able to raise the sides of the chassis for less rubbing in tight corners and high speeds. The entire drivetrain sits as low as possible in the chassis, for less "lurch" than with normal dual-belt designs. This low CG (Center of Gravity) design will help make the Pro 3 one of the easiest to drive cars you'll ever try!

One of the most overlooked features of the Pro 2 was its unique body mounting system, which use sliding caps that allowed you to change bodies without requiring new mount pieces. By simply moving the cap up or down and inserting the clip in a new hole, you could alter the body mount height by as little as 1mm. We've carried this same system over to the Pro 3, using the same body mount positions that all HPI 1/10 scale Touring Cars use. You won't have to drill new body holes for the Pro 3! As a new feature, our designers have also included new body mount positions that are spaced much wider than normal, for extra stability and less "body rattle".

All-new suspension optimized for 190mm, with a wider front track than the RS4 Pro 2

Angled chassis for reduced rubbing in corners

Stainless steel hinge pins held in place without e-clips!

Improved diff access front and rear (approximately half the screws of the Pro 2)

Extremely low center of gravity locations for batteries, motor, electronics and drivetrain

Front bumper brace with transponder mount

Adjustable fine-pitch front and rear body posts

Optional mounts for wide-offset body posts that provide more body stability

New stronger front bumper is easily removed (4 screws, no chassis disassembly required)

Pre-cut foam bumper included

New stronger HPI ball cups

Easy access to speed control and battery/motor wiring

Increased room for electronics

Servo wires pass under battery for neat installation

Accepts stick pack, side-by-side, or saddle (3 + 3) battery packs

Drivetrain

The drivetrain of an electric Touring Car is so important, and the Pro 3 drivetrain is so new, that we decided our new drivetrain deserved a whole section for itself!

We start with a motor mount that features horizontal sliding motor mounts so the center of gravity is not affected when new spur gears or pinion gears are installed. The motor mount is aluminum for superior heat dissipation and purple anodized for stealthy good looks. The Pro 3 uses standard 64 pitch spur and pinion gears, so they are easy to find at any hobby shop. "Long shank" HPI pinion gears or standard pinion gears from a variety of companies will fit on the motor shaft and reach the spur gear easily.

The spur gear mounts to a 16 tooth pulley that directly turns the rear drive belt. This pulley also turns a strong steel gear shaft that is ball bearing supported and features another 16 tooth pulley turning the front drive belt. The drive belts are made of a special low-friction rubber compound that was originally developed for our RS4 Pro 2. Each belt turns a 36 tooth diff pulley that is the central member of an all-new 3-bearing ball diff assembly. The large diff pulley is supported by 12 individual diff balls and spins on two ball bearings for a smooth diff action. The diff outdrives are made of our extremely lightweight carbon graphite nylon material for a drastically reduced rotating weight over standard steel diff outdrives. The internal drive ratio of the Pro 3 is 2.25 (diff pulley of 36 divided by the gear shaft pulley of 16). The Pro 3 will come with a 116 tooth HPI spur and a 35 tooth HPI pinion. Either long- or short-shank pinions will fit the Pro 3.

The diff outdrives spin MIP's patented Shiny CVD's at each corner. The CVD (Constant Velocity Drive) system from MIP is the ideal rebuildable universal dogbone solution, and we're proud to feature genuine MIP parts and replacements in the RS4 Pro 3. Shiny CVD's use a special strong steel alloy for amazing strength, and our engineers went the extra step to make the hub bearings front and rear the same size, so you don't have to worry about extra spare axles or bearing sizes to carry around! The Pro 2 was the first production Touring Car to feature MIP CVD's, and we're happy to provide them with the Pro 3.

Just in case you ever have to tension the belts, the longer front belt is easily adjusted with a sliding ball bearing belt tensioner, and the shorter rear belt can be tightened or loosened as easily as removing the rear diff assembly. Rear differential access has been made amazingly easy, with less than half the number of screws necessary for removal when compared to the Pro 2!

Lowered drivetrain system

MIP Shiny CVD's front and rear use same bearing sizes for lower spare parts requirements (front and rear axles are the same)

Lighter drivetrain (smaller spur gear, carbon graphite ball diffs, short MIP CVD's)

New internal drive ratio combines with lighter drivetrain for amazing acceleration

Low-friction dual belt drive system

Front and rear externally adjustable ball diffs, no disassembly required

Carbon graphite ball diff outdrives approximately 50% less rotating weight than metal outdrives

Horizontal motor mounts

24 ball bearings

Front ball bearing belt tensioner and rear hex cam tensioner standard

Purple anodized aluminum motor mount

Fits long- or short-shank pinions for easy compatibility

Steering

The industry standard bellcrank steering system is retained for the Pro 3, making it easy for anyone to understand and adjust. Shorter steering arms are harder to break in a crash, while the entire steering system is protected by a spring-loaded servo saver arm. The new short steering arms also feature new Ackerman link locations for optional steering characteristics for experienced racers. The steering arm link is also adjustable using a simple turnbuckle, providing extra tuning adjustment.

Ball bearing steering is also standard, thanks to the requests of many Pro 2 racers!

New narrow bellcrank steering system

Dual ball bearing supports

Optional Ackerman locations

Strong spring-loaded servo saver built into the bellcrank steering system

Option Parts

We realize that many serious racers like to have different option parts available for their kits to help them tune the car to suit their driving style or chosen racing surface. We have several option parts available now, with more on the way, including:

Front one-way differential for extra straight-line speed and increased turning

Available NowOne-way front pulley for extra straight-line speed and increased turning

Graphite molded plastic parts for increased durability and less chassis or arm flex

Available NowAluminum MIP CVD bones for lighter rotating drivetrain weight and faster acceleration

Available NowFinned purple aluminum motor mount and heatsink for increased heat dissipation and higher motor gearing

New sway bar set for many extra tuning options

Currently available parts that will fit the Pro 3 include the following:

Any of our 24mm wheels, tires and Pro Molded Inner Foams

Pro Linear Springs (#6841 to #6849)

Aluminum Threaded Shock Set (#72170)

Aluminum Hex Clamp Hubs (#72036)

plus option cone washers and titanium or aluminum screws

Part #178

The box is real, the car is not.

Build your own small Pro 3 box for fun! Print on heavyweight inkjet paper for best results.

See our kit video! | See our Customer's touring cars