Different rim sizes = speedometer reading wrong? - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

jrcase · 02-08-2010, 08:20 AM

With the 2SS offering both 20" and 21" wheels, it seems to me that the speedometer will be inaccurate on one of the packages. What does GM use as a baseline calibration for the speedometer, the 20" or 21"?

Also, does the V6 18" use the same calibration? It seems to me that with all the different sizes, someone's speedometer is going to be off.

camaro1 · 02-08-2010, 08:22 AM

rim size has nothing to do with the speedometer, they all have the same overall tire height

Buckbo · 02-08-2010, 08:29 AM

Quote:

Originally Posted by camaro1

rim size has nothing to do with the speedometer, they all have the same overall tire height

I was thinking that too. The rubber sidewall is shorter to compensate for the larger rim but overall the total height should be the same.

Sir Nuke · 02-08-2010, 10:48 AM

HDDAN · 02-08-2010, 11:04 AM

Quote:

Originally Posted by camaro1

rim size has nothing to do with the speedometer, they all have the same overall tire height

You are right. I read that GM used the same outer diameter on all of the tires so that they would only need one speedometer.

g-townmach · 02-08-2010, 11:33 AM

Speedometer goes off revolutions of overall diameter of rear wheels/tires. Go to a bigger rim, you put a shorter sidewall tire on to get the same diameter as before. However, if Chevy wanted to create different diameters between the 18's, 20's and 21's with their tire sizes they could have b/c a speedo can be calibrated easily to correct tire sizes.

02-08-2010, 08:20 AM	#1
jrcase Drives: 2010 Black/Black 2SS Join Date: Jan 2010 Location: Knoxville, TN Posts: 22	Different rim sizes = speedometer reading wrong? With the 2SS offering both 20" and 21" wheels, it seems to me that the speedometer will be inaccurate on one of the packages. What does GM use as a baseline calibration for the speedometer, the 20" or 21"? Also, does the V6 18" use the same calibration? It seems to me that with all the different sizes, someone's speedometer is going to be off.

02-08-2010, 08:22 AM	#2
camaro1 Drives: 550+RWHP 2010 camaro Join Date: Sep 2007 Location: wisconsin Posts: 1,588	rim size has nothing to do with the speedometer, they all have the same overall tire height __________________ 415ci stroker, TVS 2300 Magnacharger, cnc heads, cam, yank ss3200 converter, Kooks long tubes, Bwoody true cold air kit, ZL1 Pump, magnaflow 3" cat-back, lowering springs,BMR control arms and tie rod bars, 3.73 gears, diff mounts, RX can, ADM fuel controller

02-08-2010, 10:48 AM	#4
Sir Nuke Master of All Things Drives: '20 Corvette Stingray Join Date: Jul 2009 Location: Southeast of Houston, Texas Posts: 22,331 View My Garage	__________________

02-08-2010, 11:33 AM	#6
g-townmach I FARTED Drives: 2010 2SS/RS Join Date: Nov 2009 Location: cen-tex Posts: 870	Speedometer goes off revolutions of overall diameter of rear wheels/tires. Go to a bigger rim, you put a shorter sidewall tire on to get the same diameter as before. However, if Chevy wanted to create different diameters between the 18's, 20's and 21's with their tire sizes they could have b/c a speedo can be calibrated easily to correct tire sizes. __________________