I just put 225/45 R17 Toyo Proxes 4 on my 2001 SE 17” oem rims. I knew that since the size was different, I would be going slower than the speedometer reading and running less miles than the odometer reading. Since the tire specifications allowed for 7” rims however, I wasn’t worried about any safety compromises.

Recently however, I came upon 1010tires.com and found their tire size comparison calculator. I punched in my old tire numbers and my new tire numbers, and was told that the difference in the diameters was greater than 3%, and that I might experience brake failure. (Just for the record, my own measurements of the actual differences in the tire sizes gave me only a 1.7% difference, so I am not as worried).

Does anyone have any info on whether or not a smaller tire size will affect brake performance, and specifically the ABS? I bought these tires because they were magnitudes better than the oem Potenzas—but I don’t want to create safety issues just by using a smaller size.

 

I wouldn't worry about it... my rims/tires are like 2% over stock and I have a big brake kit, and ABS still works fine.

 

Since you went with a better tire than your old stockers, it should improve your braking. Good question as far as ABS...I'm not sure how diameters affect that...anyone?

 

Thanks guys! I suppose that if ABS engagement is based on wheel speed, then with smaller tires it should only turn on a fraction sooner if anything (since it thinks my tires are going faster than they actually are).

Any idea then why they say that a 3% diameter difference over stock might lead to brake failure?