How to: HPI micro RS4 tuning guide

Radio Control Car Action, Jan 2003 by Katzer, Gary

Where, what and when to adjust your Micro

HPI's micro RS4 is ready for fast fun straight from the box, but if you plan to race your Micro, there's much you can do to dial it in for track time. We've jammed hours of track testing into an easy-to-follow tuning article. From ball diffs to one-ways, we cover it all. Clear off some room on your workbench because it's time to start wrenching!

TIRES

HPI, Trinity, Team Orion, Megatech, Dynamite, GPM and others all offer tires In various compounds and tread designs; a good thing because tire selection represents 75 percent of the dialing-in process. In most cases, you should team softer-compound tires with the stock, hard-compound tires. This is especially true if you have a 140mm Micro with an abundance of steering,

* SOFT REARS, HARD FRONTS

This combination will eliminate oversteer and will allow the car to carry more speed through the corners. If you race with a mad motor and 6 cells, for adequate traction you may need to install softer tires all around. In most cases, it's best to run a slightly harder tire in the front than in the rear.

* TIRES FOR CARPET

HPI's 4719 high-performance wide tires are specially designed for carpet. Teaming these rear tires with the stock hard front tires is the ticket for racing on Ozite. Depending on how your car turns, you may or may nut want to "sauce" the front tires with traction compound. Experiment by applying traction compound only to the front tires' inside halves or outside halves.

WHEELBASE & WIDTH

The Micro can be set up with a 140mm or 150mm wheelbase. The 150mm setup is usually more stable, and that makes it ideal for high-speed tracks with wide, sweeping turns, The shorter 140mm setting is not as stable, but ft offers more aggressive steering; this makes it ideal for tighter, more technical tracks.

Front and rear width or "track" will also affect the way a car handles. As a rule, a wide track with a short wheelbase (a "square" footprint) has more steering and less rear bite; a more rectangular footprint (narrow track with a long wheelbase) has more rear bite and less steering.

SHOCK DAMPING

The Micro doesn't have the oil-filled dampers found in larger Rio-scale sedans, but its shock damping can still be tuned by altering the thickness of the grease used to lubricate the shock shafts.

* THICKER GREASE (more damping)

If your car tends to have too much steering or it spins out easily, apply a thick lube to the front shock shafts. Tamiya Anti-Wear Grease and Associated Black Grease work well.

* THINNER GREASE (less damping)

If the car pushes or doesn't transition as quicky as you like, lighter damping can help; just apply thinner grease.

* REAR SHOCK TIPS

The same principles apply to the rear shock: if you want to increase steering by taking away rear traction use a thicker tube on the rear shock; if you need more re Tear bite, use a thinner tube. A little tube on the shock shafts is all it takes.

REAR DIFFERENTIAL

The Micros tear gear diff does a decent job, but a ball differential will operate more smoothlyy and can be adjusted for looser or firmer action (never set the diff so loosely that it slips). HPI, Dynamite, Megatech and others offer ball diffs that work very well.

* LOOSER SETTING

A loose setting increases rear traction when cornering, but it may also cause the diff to "unload" more easily on high-traction surfaces that cause the car to unweight its inside tires in tight turns.

* TIGHTER SETTING

When You use tighter diff settings, the car will have less rear traction when cornering because more force will be required to activate the diff. If traction isn't sufficient to activate the diff while cornering, the inside wheel will have less traction as the diff tries to turn it as quickly as the outside rear wheel.

FRONT DIFFERENTIAL

The Micro's front gear can be tuned by installing a stiffer or softer spring between the brass planetary gear HPI's tuned spring set includes soft and firm cliff springs.

* SOFTER SPRING

Installing a softer spring allows the front diff to rotate more freely and will enhance steering.

* STIFFER SPRING

A stiffer spring will slow diff action and reduce front steering.

* FRONT ONE-WAY

If you really want to free up your drive train and improve your carts high-speed steering, try installing a front oneway diff. The front one-way provides full power to all four wheels during acceleration, but allows the front wheels to freewheel during coasting and braking. A one-way also gives a car more high-speed steering, but it will have rear-wheel braking only. If your transmitter has endpoint adjustments, use that feature to adjust the brake throw so full brake power falls just short of locking the rear tires. When using a one-way, HPI suggests an upgrade to steel or aluminum universal axles, as a one-way setup puts a greater strain on the axles,

SHOCK SPRINGS

HPI, Team Orion, Megatech, GPM and several other RC sources offer color-coded tuning spring sets for the Micro. Orion's spring set includes red springs (stiffer than the stock, black springs), and blue springs (softer than stock). HPI's set includes "medium firm" green springs and "firm" blue springs, both of which are stiffer than the stock HPI black springs.