just don't want the ABS to quit at the Glen. My 205/40 17 Toyo RA1's were causing the ABS light to come on. It was fine and didn't quit at Lime Rock mostly because you don't go straight long enough for the system to see the difference in wheel speed front to back, but I bet at the Glen it won't be fine.
Scott

 

What size rears are you running? We need more information.

 

There is a very cool tire size calculator HERE. Front to back should not be different by more than 3%, I have read. Note, you want to input the front and rear tires that you will actually use in the calculator.

 

Matt, running 255/40 17's rear and 205/40 17's front. According to Vilvan tire I can't get the 225/45 17 because Toyo does not make the RA1 in that size.....

 

They do make a 235/40 and 235/45 17's.

Checking the Toyo website, I got the following circumferences

205/40 = 23.5 inches
235/40 = 24.4 inches
235/45 = 25.4 inches
255/40 = 25.0 inches

The 205's and the 255's have a difference of 6% - However, the 235/40 and 235/45 both have only a 2% difference than the 255's. I've run the 235/255 setup for years with no ABS issues. The only issue you may run into is that the 235 is a marginal fit on a 7" rim. It fits much better on a 7.5 or 8 inch. If you run on 7's - you may want to add an extra pound or two to the fronts to keep them from rolling over.

 

I ran the 235x45 and the 255x40 rear without any issues...

 

I just ordered a pair of Toyo RA1's in the 235/45/17 and 255/40/17's based on a friends experience who's currently running this set up with RS height, not anticipating any problems.