This is the logic behind having new tires on the rear
(TireRack employee's visited Michelin's test track and were given cars with worn fronts or rears)
m.tirerack.com/tires /tiretech/techpage.j sp?techid=52It didn't take long for this hands-on experience to confirm that the "proving grounds" name for the facility was correct. The ability to sense and control predictable understeer with the new tires on the rear and the helplessness in trying to control the surprising oversteer with the new tires on the front was emphatically proven.
And even though our drivers had the advantage of knowing we were going to be challenged to maintain car control, spinouts became common during our laps in the car with the new tires on the front and the worn tires on the rear. Michelin advises us that almost every driver spins out at least once when participating in this demonstration!