Over the summer I got a set of 15x7.5 Q45 rims. I kept my 215/60/15 Potenza RE950's because they were almost brand new. I thought that using the 215/60 on a 7.5" rim would be pushing it a bit but the Bridgestone pecs allow up to a 7.5" rims so I just kept the tires.

I think I have lost a little bit of cornering grip. Does stretching the tread like this affect the tires performance.

 

normally streching the tire reduces the side wall flex.... so you may not have lost grip just able to push harder with out the tire rolling ... making it fell like you have less grip.. also the break-away.. when the tire turns loose feels sharper with less sidewall flex.... I don't think a 215 on a 7.5" wheel is too much strech... later