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Retired LEO meow
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14,535 Posts
Discussion Starter · #1 ·
I was wondering if when someone ordered the optional 18" wheel, did the factory recaliberate the new tire diameter into the PCM so the mileage would not be off over time? I figure over time the miles on the odometer would be different of someone was running with 17's than someone running with 18's.
 

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New PB MPH - 127.54
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2,376 Posts
Who cares....you avitar is amazing!



Thats a good question. Staying tuned in for an answer...
 

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05 Torrid Red Pontiac GT0 6MT
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1,096 Posts
The tire size is different for the 17's v. the 18's. The outside rolling diameter is almost exactly the same so no "recalibration" is necessary. It's well within specs.

Update: The 18's circumference is .8" longer. So your speedo will be running about 1% off. I think factory specs on speedo’s are +- 3%
 

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Retired LEO meow
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14,535 Posts
Discussion Starter · #5 ·
smyla said:
I think factory specs on speedo’s are +- 3%
That is correct. GTPprix advised me of that when he was activating the shift light for me. Chris corrected that problem.
 
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