Tire size change issues with abs etc.

[kenand1988]

2015 C7 Z06 m7

front 285/30/19
rear 315/35/20 stock is 335/25/20

After putting on the new tires did a quick drive and dash lit up like a christmas tree. Tried using the tire/change wizard but 1) noticed it is probably not for a staggered setup because you can only input one tire size not a front and rear. I read some about changing vss pulse per rev or vss tires per rev but I feel like I could go down a rabbit hole with that if I'm not sure what I am changing. I know this can be remedied without changing my fronts as well, if anyone could help that would be great.Z06 IW9 Haltech FF Final.hpt

[gtstorey]

That’s a rear diameter of 28.7 and a front of 25.7. I don’t think that is going to work. It thinks the car is loosing traction all of the time and that isn’t handled in the ECM.

[kenand1988]

That?s a rear diameter of 28.7 and a front of 25.7. I don?t think that is going to work. It thinks the car is loosing traction all of the time and that isn?t handled in the ECM.

When measured the stock rear was 26" and the new rears are 27.5? which is a 6% difference. I'm pretty sure that's not so extreme that it can't be made to work.

[gtstorey]

I’m assuming the stock fronts are similar in diameter to the stock rear? If so the abs/traction control can only handle a small difference between front and rear. The number I’ve always heard was about 3%.

[kenand1988]

The stock fronts are 285/30/19, they are not close to the size of the stock rears. I just measured the fronts and they are 25" so they were an inch smaller than the rears to begin with. I have only changed the rears.

[TriPinTaZ]

There is currently no way to tune around this. Your tire height difference is too great for the BCM.

[Alvin]

It can cause odd driveablity issues too.

[kenand1988]

Assuming I were to go up in the front to keep the height difference under 4% would there be anything to tune other than correcting the speedo? I had a local tire shop tell me even if I increased the front tire size I would still have traction control issues as the car would be sitting about 1 inch higher now. Everything I have read and heard so far has said if the front to rear difference is small enough there shouldnt be any issue at least with abs and tc.

[gtstorey]

Everything I have read and heard so far has said if the front to rear difference is small enough there shouldn't be any issue at least with abs and tc.

That "small enough difference" is pretty smaller, and probably getting smaller with each generation.

[kenand1988]

But the question is if you keep the difference small enough does it matter how tall they are. In stock form the difference is slightly over 3%.

[gtstorey]

But the question is if you keep the difference small enough does it matter how tall they are. In stock form the difference is slightly over 3%.

I don't know the answer. My guess is it will probably work since none of the sensors are doing more than counting wheel revolutions.

[blindsquirrel]

Pretty sure what you need to change is not in the ECM/TCM, it's in either the BCM or ABS/TCS/VSES.

[kenand1988]

Pretty sure what you need to change is not in the ECM/TCM, it's in either the BCM or ABS/TCS/VSES.

Yep, that's the problem. So the only alternatives are live with it, go bigger in the front or put stock rears back on.

[gtstorey]

You might go through the exercise of changing the tire size settings that affect trans and speedometer on the slim chance there is a logic check between the wheel sensor and the speedometer/transmission. I doubt it will work though.

Have you checked codes for all the modules including abs and traction control?

[kenand1988]

You might go through the exercise of changing the tire size settings that affect trans and speedometer on the slim chance there is a logic check between the wheel sensor and the speedometer/transmission. I doubt it will work though.

Have you checked codes for all the modules including abs and traction control?

Its a c0245 wheel freq error code

[gtstorey]

Might be worth digging enough to find the service manual info for that code and confirm what it’s telling you. It sounds like it doesn’t like the frequency readings of the wheel sensors but I guess it could still be different readings of the VSS to wheel speed.

[kenand1988]

Yes I thought maybe adjuster the pulses per mile or revs per mile could get everything happy again. Tried maybe 7 tunes with different settings but don't really know what I'm doing. Some tunes seemed to make it take longer for the code to pop. Some tunes would basically pop the code instantly.

[blindsquirrel]

C0245

Conditions for Setting the DTC

Wheel speed differences between one wheel and the others is greater than 5 percent.

[gtstorey]

I wonder if that 5% is in excess of the built in difference with different stock wheel sizes? Or is it just total difference which would mean that size changes of about any magnitude would screw it up?

OP, we have been talking diameter, but you should probably do a roll out to get the circumference for a more accurate measurement. But I doubt anything other than maybe increasing your front tire size will make this work. And you will steel need to get the vss/pulses/mile worked out to get the speedometer to work.

[TriPinTaZ]

There are tried and true setups posted on Corvette Forum that won't cause an issue with the BCM. Pick one and go with it. There is no other fix.