McHenry Forum - Crash Reconstruction & Simulation

Q: Can anyone point me in the direction of any studies/papers in relation to the effect (if any) bald tyres would have on a vehicle going into a yaw on dry, level bitumen?

A: When you replace tires the recommendation is to put the old tires on the front. Why? Because newer tires with more aggressive tread have a higher cornering stiffness than worn tires and ya don’t want your front tires ‘making promises your back tires can’t keep!'
Obviously a bald tire might have a greater difference than simply worn v new tires.
From Gillespie: Fundamentals of Vehicle Dynamics:

• “Cornering stiffness is oneof the primary variables affecting steady-state and transient cornering properties of vehicles in the normal driving regime. A higher relative cornering stiffness on the rear wheels is necessary to achieve understeer. Higher stiffness at the front wheels will produce oversteer, unless compensated by other factors, and may result in a vehicle which has a critical speed above which it becomes unstable.”

So…In your situation, the question is where was the bald tire? And what shape were the other tires on the vehicle? And if the bald tire were on the rear, was the combined cornering stiffness of the rear (1 bald, one ‘normal’ or similar to the front) that dissimilar to the combined cornering stiffness at the front (two ‘normal’ tires?) such that it caused the vehicle to be ‘oversteer’ and/or have a critical speed? And was the vehicle traveling at or above the ‘critical’ speed?
I’d suggest looking at a number of recent SAE papers on the tread separation tests since a tire without a tread (after the tread separates) may be substantially similar to a bald tire (there may be some issues related to presence of a steel belt wires, etc?)
Also look at Systems Technology as they did some tests on tire intermix mainly with respect to radial v steel belted but which may have some relevance.