Dealer says they can't correct speedo for different wheel/tire sizes??

[Jason@JacFab]

I've seriously been contemplating switching to 18" wheels and tires, but really don't want the speedo to be off. I figured the dealer could just plug in and reprogram for the different wheel/tire size, done deal and away we go. They said that GM pulled that capability several years ago?! WTF? Really? I figured that would be the way to go, take it down to the dealer, not mess with a handheld programmer or a tune, but they say they can't even do it?

Then the dealer guy said that the only way I could do it is if I got a programmer, and that could correct the speedo... Well yeah, I knew that, but didnt want to mess with that because it could potentially void the warranty... Then he went on to say that even if all I used the programmer for was to JUST CORRECT THE SPEEDO, that it would void my powertrain warranty... What a bunch of bull! Anyone else hear anything like this?

[Blue17CamaroZL1]

I can't say for GM pulling the capability to reprogram the PCM but yes, you can use a program like HPTuners to reprogram the PCM to correct for new wheel size.

However, it by using that type of programming, the dealer can see the change in programming and can possibly void your warranty.

[Jason@JacFab]

I know about any kind of tuning via programmer, or tune voiding the warranty... It's just really disappointing that I can't even change wheel/tire sizes without voiding the warranty.

[5cents]

I don't know, that's kinda hard to believe that the dealer can't reprogram the speedo. People change wheel sizes alot more now days that they did in the past.

[SSMickey]

I would suggest sending "Nineball" a PM. He might have a suggestion for an alternative.

[Globemaster]

Did you call any other dealers to see what they say?

[Sterling]

What's wrong with switching to 18" wheels, but keeping the tire diameter the same.
The tire diameter is the same on the 18" wheels that come on the LS/LT models as it is on the 20" SS models. No speedo correction is necessary that way.

[Sir Nuke]

RacnJsn95, just like Sterling stated above^^^, regardless of waht DIAMETER TIRE/WHEEL combo you put on your car, as long at the tire diameter is the same, or very very close, it won't change your speedo.....example: I have a LT....LT's come fron the factory with either 18's or 19's.....OR you can opt for the 20's upgrade and there is NO difference or reprogramming required by the factory OR a dealer.

[gml1998]

See this thread
camaro5.com/forums/showthread.php?t=62838&highlight=tire+rim+sizes

[suplex]

Try this tire size calculator out:

http://www.miata.net/garage/tirecalc.html

All you do is input your current tire size, then play a little bit with the size you would like to get and it tells you how close your real speed would be when driving 60mph (for example).

I have 18" Wheels on my 1LT and you can use my tire size as a reference: P245/55-R18.

[Stex]

You can change tire wheel dia/circum quite a bit without throwing speedo off too much..my dealer say about three sizes either way before you need to program and they can do it...this tool will tell you how much you are off...

http://www.miata.net/garage/tirecalc.html

[Hannibal]

BTW, if you have brembos, the steel 18 inch stock Camaro wheels will not fit. The brakes hit the wheels.

That said, others here are correct. As long as the diameter stays the same, no speedo change is needed. The guys who go from stock 18s to the 20 inch stock setup have no overall diameter change.

[Jason@JacFab]

The tire I plan to run is a 26.97" diameter, where is the oem p-zero is 28.66". According to a tire size calculator I found, it's a 5.9% difference in diameter, and the speedometer will read 6.269% too fast (IE speedo will read 63.7mpg when I am really going 60)... If the calculator is right... I can deal with that, I didn't just want to be running around getting speeding tickets.

I haven't bought a programmer yet because I knew it would void the warranty, big I figured for sure my local dealer could change the speedo to read right while retaining all factory warranty.

I will be running the Corvette 18x9.5 all the way around. They clear the SS brakes.

[Fiftydriver]

Originally Posted by RacnJsn95

I've seriously been contemplating switching to 18" wheels and tires, but really don't want the speedo to be off. I figured the dealer could just plug in and reprogram for the different wheel/tire size, done deal and away we go. They said that GM pulled that capability several years ago?! WTF? Really? I figured that would be the way to go, take it down to the dealer, not mess with a handheld programmer or a tune, but they say they can't even do it?

Then the dealer guy said that the only way I could do it is if I got a programmer, and that could correct the speedo... Well yeah, I knew that, but didnt want to mess with that because it could potentially void the warranty... Then he went on to say that even if all I used the programmer for was to JUST CORRECT THE SPEEDO, that it would void my powertrain warranty... What a bunch of bull! Anyone else hear anything like this?

They "Can Not" or they "WILL NOT". I think the latter is more correct. You can correct the speedo for gear changes, why could you not adjust it for tire diameter as well, does not make much sense.