Can Wheel Diameter Be Reprogrammed?

ChrisSlicks

Can Wheel Diameter Be Reprogrammed on the 370?

My dealer/tech says no, but I know that some cars can. It would make sense to me as it's all electronic just to have a programmed value for RPM (Revolutions Per Mile).

wstar

Yes, all modern cars can (and should, perhaps must?) be reprogrammed when changing the revs per mile (technically, the circumference of the outer surface of the wheel). At the very least, not doing so will throw off your speedometer, odometer, and anything else based on those values.

I would imagine that VDC is somewhat reliant on these values as well for the more advanced stuff, although not for basic operations that merely rely on the relative RPM of each wheel like ABS. I suspect if it does cause any VDC problems, VDC will sense the incoherent inputs and disable itself (that's what it did when I reinstalled my steering shaft slightly off-center. It must have figured it out from the yaw sensor input and/or relative wheel RPMs).

I would assume that any Nissan dealer should be capable of setting this up with their CONSULT equipment. Aftermarket ECU stuff like UpRev Cipher/Osiris and Cobb AccessPort should be able to do it as well. Unfortunately, none of the consumer programming stuff has been released yet.

The dealer you're talking to has to be full of crap. There's no way that Nissan's official response to changing your tire circumference is "screw you the car is just going to calculate some things wrong".

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ChrisSlicks

Thanks wstar.

I have to think that it would be possible, I don't know why they would say that it can't unless they simply just don't know how?

My tire sizes are actually closer to each other front to back than the stock ones were but slightly smaller overall (around 1%). Shouldn't be enough to cause a problem, never has before.

alan93rsa

The NSX's used to have a problem with the % change front/rear. If you didn't worry about the traction control you could just turn it off.

Porsche 4 wheel drive cars have an issue with the front/rear sizes.

I don't know that it would affect the Z as much. Can you find someone that you can swap setups with to see if it makes the problem go away.

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ChrisSlicks

Not many local Z's around here yet. I don't think the tires are the issue but it would be nice to rule it out as a possibility.

semtex

Oh...are you thinking that this is the cause of that weird braking issue you had?

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ChrisSlicks

I really don't think it is as braking starts perfectly normal until things heat up, but so far tires are the only thing I've changed so it remains a possibility. Unfortunately I never did an event on the stock tires so I have no frame of reference. If the problem persists I may have to remount the stock tires to prove that point.