Different wheel diameters' effects on TCS
 

Right now I have a 235/40R17 square setup. It's great and all, but I need a little more traction out back.

I came across a deal for almost free (good buddy getting rid of one set of track tires for another) 255/40R17 tires.

I was thinking of running the 255/40's out back on 9" RPF1's.

Would the discrepancy between 235/40 and 255/40 be too much for the traction control?

Thanks in advance!

You can compare the two using this calculator below. Basically, the calculation shows they are within the 3% tolerance frame that would affect TCS. So no issue.

http://www.1010tires.com/Tools/Tire-Size-Calculator

Ya I just am hesitant. A 2.5% difference is not that far from 3%.

I guess I'd like to hear from someone who has run different sizes and had no issues before I go and spend the $ to acquire the 9" rims.

i am running 18x9.5 all around with 225/40 front and 255/35 rear with no issues.

Yes but you are running 255/35. I am talking about running 255/40.

my tires are still different diameters height and width, if anything a greater difference then a 40 side wall. So my point was if i dont have issues, you shouldn't.

Again....that's not how tires work. A 225/40 has a circumference of 2,002 mm. A 255/35 has a circumference of 1,997 mm. This represents a difference of 0.2%.

My proposed setup has a difference of 2.5%. Over 10 times your difference.

You essentially have identically sized tires. Now they are bigger than stock yes, BUT.....they are basically the same diameter front to back. Your car doesn't care if you have tiny hotwheels tires or giant tractor tires. All it cares about is that all four are the same diameter.

You could always not run a staggered set-up that would increase understeer.