TRACK FRICTION – DRIVE WHEEL MATERIAL & THE USE OF TYRES
When using an electronics unit most cars exhibit wheel spin on takeoff from the start line, particularly in high Sun conditions. This costs race time, in fact the addition of a tyre even with its slight increase in rolling resistance will give a lower race time. One suggestion to reduce the need for a tyre, is to use an aluminium drive wheel which has a higher friction coefficient than a plastic wheel.
Aluminium though is significantly heavier than plastic. To evaluate this suggestion a test was conducted to determine the difference in friction coefficient between plastic (acetal) and aluminium. The test was conducted on a section of Box Hill track (blue track) using the test car Photon Cruncher MK II. For testing the car was placed on the track which was angled up slightly to ensure a constant load on the force measuring equipment.
The car was towed up this ramp and the force required to pull it with all wheels free was measured at 65 gm. The downward force on each rear wheel due to gravity was measured at 840 gm. The rear drive wheel was then locked and the towing force measured. This test was conducted with both an aluminium and a plastic wheel with no tyre fitted.
With the aluminium wheel locked the force to tow the car was measured at 340 gm. With the plastic wheel locked the force to tow the car was measured at 295 gm. By subtracting the 65 gm. required to tow the car with wheels free the actual force required to overcome the locked wheel is obtained, this force is the maximum possible drive force at this loading condition.