speedometer reading
Thread Starter
Intermediate
Joined: Oct 2018
Posts: 26
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From: Dalmeny, SK
speedometer reading
Hi, I am wondering where/how the C5 Z06 measures the speed. Does it have a transmission gear or does it measure tire rotation? I am wondering if I change the wheel size from 17" in front to 18" if that will affect the readings.
Le Mans Master
Joined: Sep 2014
Posts: 5,278
Likes: 540
From: Kelowna BC
No, it will not affect the speedo. But it may affect your AH if you don't still allow for a smaller diameter front. What size fronts are you planning? Factory 18's with 275 or 285-35?
The speedo is at the rear, post diff.
The speedo is at the rear, post diff.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
The speed signal comes from a sensor on top of the differential. It reads a toothed ring gear on the ring gear. Its called a (TONE WHEEL) The wheel speed sensors only provide individual wheel speeds for the EBTCM to help calculate info for anti lock brakes and Active Handling (if you have that option)
Thread Starter
Intermediate
Joined: Oct 2018
Posts: 26
Likes: 0
From: Dalmeny, SK
What do you mean by AH? I was thinking that I would use the same factory wheels as the 18" in the rear for the front.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
ACTIVE HANDLING (AH)
The EBTCM has a SET wheel diameter ratio front to rear that it uses to properly calculate what it needs to do to pulse or apply the brakes to prevent wheel lock up during heavy braking or IF you loose traction (STABILITY) in a turn or poor road conditions if you have (Active Handling). If that proper wheel size (RATIO FRONT TO REAR) is not correct, the EBTCM will error out and NOT and revert to manual braking.
Bill
The EBTCM has a SET wheel diameter ratio front to rear that it uses to properly calculate what it needs to do to pulse or apply the brakes to prevent wheel lock up during heavy braking or IF you loose traction (STABILITY) in a turn or poor road conditions if you have (Active Handling). If that proper wheel size (RATIO FRONT TO REAR) is not correct, the EBTCM will error out and NOT and revert to manual braking.
Bill
Le Mans Master
Joined: Sep 2014
Posts: 5,278
Likes: 540
From: Kelowna BC
You can, many do, I probably will when my tires expire... but as BC said, you need an offset outside diameter to avoid Active Handling issues. Fronts should be around 3/4 to 1" shorter. So running a 275-35 with 295-35, or 285-35 with 305-35 rears IIRC keeps things intact.
