Correct tire diameter input to PCM for speedo
Thread Starter
Burning Brakes
Joined: Jul 2018
Posts: 1,113
Likes: 144
From: Miami
Correct tire diameter input to PCM for speedo
Hi guys, just got my ‘new to me’ wheels and tires. I now run the C6Z06 OEM sizes Fronts 275/35/18 and Rears 325/30/19.
My questions are:
1. Which wheel speed inputs on the PCM for vehicle speed? Fronts? Rears?
2. Then what would be the correct tire diameter value I should give to my tuner now to recalibrate my speedo?
My questions are:
1. Which wheel speed inputs on the PCM for vehicle speed? Fronts? Rears?
2. Then what would be the correct tire diameter value I should give to my tuner now to recalibrate my speedo?
Thread Starter
Burning Brakes
Joined: Jul 2018
Posts: 1,113
Likes: 144
From: Miami
I don’t think so. Mine is a 1999 FRC. I believe these were 17/18 setup originally, and C6Z06 are 18/19. Tire diameter must be different. Ok, but now I know it’s the rears that do the reading.
Last edited by turabo87; Jan 27, 2019 at 08:45 AM.
Acct Suspended APR 2026 by request
Joined: Dec 2010
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2020 Corvette of the Year Finalist (performance mods)
C5 of Year Winner (performance mods) 2019
you need someone with hptuners or another tuning program (handhelds might even work) to change the rear tire height to what you have on the car
Melting Slicks
Joined: Oct 2010
Posts: 3,032
Likes: 795
From: Tollesboro Kentucky
The 275/40-18 tire is exactly the same diameter as the 325/30-19 tire.The sidewall is shorter on the 19.That makes up for the difference in wheel diameter.
Thread Starter
Burning Brakes
Joined: Jul 2018
Posts: 1,113
Likes: 144
From: Miami
Gotta admit, you were right all along. The proof is in the pudding: I verified speedo speed vs. GPS speed on phone and it was spot on up to 90mph. Thanks.
