Are ABS and TCS ok with 27/26 Rear/Front Tire Diameters?

[Gary Smith]

I will be taking my 2017 GT back to Thunderhill soon. Will there be ABS or TCS problems if I mix 26-inch diameter front tires with 27-inch rears? No lights after 40 miles of highway testing but none of this was aggressive or high speed. I’m just wondering whether there might be some surprise at the track.

 

[JDee]

I have a set of 285/19s front and 305/19s rear I use for rain tires and ran them once in the dry, there's about 3/4 inch difference in diameter. No issues with ABS or TCS.

 

[Gary Smith]

Thanks JDee, it is reassuring to know that 3/4-inch difference is ok. I knew that 6/10-inch is ok because the stock PP tire diameters are 27.7 / 27.1 inches. It could be that the car "learns" the difference. I'm asking here because an older car I had complained with a 1-inch difference.
-Gary

 

[Norm Peterson]

Thanks JDee, it is reassuring to know that 3/4-inch difference is ok. I knew that 6/10-inch is ok because the stock PP tire diameters are 27.7 / 27.1 inches. It could be that the car "learns" the difference. I'm asking here because an older car I had complained with a 1-inch difference.
-Gary

For your new car, you'd only be making about a 1/8" difference in tire diameter stagger going from 0.6" to 0.75" difference. That's about a half percent change; feel free to ignore it.

I'm going to guess that your older car was originally equipped with either same-size tires all around or with front and rear tires of closely similar diameter (i.e. 255/45-18 paired with 285/40-18).

The usual guideline is 3%, which really represents a 3% change in front vs rear tire revs/mile away from whatever the car was originally equipped with. Not necessarily a 3% difference between the front and rear tire sizes themselves.


Norm

 

[Gary Smith]

From 27 to 26 is closer to 4% than 3 but I have now driven more than 100 miles and have engaged ABS multiple times with no lights/codes so that pretty much shows that 26/27 front/rear diameter is not a problem.

In case anyone is wondering, my questionable setup is front 255/40R18 on 9-inch wheels with rear 285/40/R18 on 10-inch wheels. All four tires Continental EC Sports. How I arrived at this setup is too boring to relate.

Thanks all, Gary