WHEEL SLIP:
- When using an electronics system it is possible and in fact common to experience
wheel spin on takeoff in high Sun. This will cost race time.(We have measured
0.2 seconds in testing.) Either increasing the weight on the drive wheel or fitting
a tyre which unfortunately also increases rolling resistance can improve this
situation.
APPENDIX P:
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.
Test conditions Towing force gm. Coefficient of Friction
No Tyre Aluminium wheel locked 275 0.327
No Tyre Plastic wheel locked 230 0.273