Why Front Wheel Drive Cars Need Good Rear Tires
A popular saying is that rear tires on a front wheel drive car only exist to keep the rear bumper from scraping on the ground. Does this mean that rear tires don't matter?
Turns out, a front wheel drive car does need reasonably good rear tires. I had an opportunity to witness this at a recent track day, which happened to be at Thompson Speedway.
I ran a pair of nearly new Toyo RR tires in the front and a pair of very worn Toyo R888 tires in the rear. I did not have a full set of RRs, thus never could get equal tires on all four wheels.
What happened during the event was the car, when driven hard, would exceed the capabilities of rear tires, primarily in corner entries. When this happened the rear tires would slide, producing oversteer. Even though the car had front wheel drive the resulting drift cost speed and was a major drag on lap time.
Taking a car that is set up to be balanced on equal tires in all positions, using much less grippy rear tires unbalances the car and the result is a significant increase in lap times.
Although I never ran a balanced setup at the same event, I suspect that having rear tires be somewhat but not excessively more worn than the fronts is likely to be fine.
An interesting question for running a front wheel drive car is whether the front and the rear tires may be treated completely independently, with the goal being to run different sizes - and perhaps different compounds - on the front and the rear axles.
My findings so far indicate that running worn out rear tires with good front tires is suboptimal. Worn out rears and good fronts is still a better setup than worn out everything.
The next option is running a dedicated pair of front tires and a dedicated pair of rear tires. While the front tires would be expected to wear out the tread (provided they are made by Toyo or Nitto or similar), the rear tires are likely to heat cycle out. Once the rear tires heat cycle out, they would be useless as either front or rear tires. The smart strategy then is to rotate rear tires to the front, or use the rear tires on another car that would wear out the tread.