Rim Size and Odometer Calibration - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

ChevyBoiler · 12-06-2009, 07:53 PM

I know this has been discussed in some other threads, but I have some actual data now that I have put my winter tires on, and the results are not what I hoped for.

I have a 2LT RS that came with the 20" rims and Pirellis. I replaced those with 18" rims and 225/60R18 Goodyear UltraGrips for the winter. This combination should have the same Outer Diameter as the 20" rims with 245/45R20 tires, so I would have expected the odometer/speedometer to not be afftected. I took it for a test drive the other day and found that my odometer calibration is incorrect. Using the milemarkers on the interstate, found that I am registering 5.0 miles traveled by the time I reach 4.7 miles by the milemarkers, so my odometer is now gaining a little over 0.3 miles for every 5.0 miles I travel. This is likely throwing off my speedometer as well, but I haven't been able to test that (can't wait to use that excuse when I get pulled over).

Anyway, just wondering if anyone else is finding similar results and what the possible solutions may be?

SS Mike · 12-06-2009, 11:23 PM

Thats weird, that size is close enough to the same size. Your 18's have an OD of 28.6299 vs. the 20's 28.6614, so it's actually barely smaller, but i wouldnt think that would make that much of a difference. Not sure why that's happening.

sting808 · 12-07-2009, 05:28 AM

I asked my dealer if they could calibrate speedo in ECM if I went through them and they said they didn't have tools to modify a lot in the ECM. At this point, the only option is aftermarket tuning that "may" void warranty.

d69chris · 12-08-2009, 01:12 AM

I would not always believe the mile markers, maybe use a tape measure.....

mjlash22 · 12-08-2009, 09:18 AM

Quote:

Originally Posted by d69chris

I would not always believe the mile markers, maybe use a tape measure.....

I wouldn't trust the markers 100% either. The GPS I have in my current car is off compared to the speedo and mile markers as well, so I'm sure with everything combined that could cause an error in the data.

Sir Nuke · 12-08-2009, 11:33 AM

I would never trust the markers.......and I believe the odometer and the speedo are linked. so if one is off, the other will be too........and since your new tires are that close, there is no way that your odometer/speedo is off that much.

BLKnCHRME09Deluxe · 12-08-2009, 11:48 AM

try this tire calculator
http://www.1010tires.com/TireSizeCalculator.asp

71cam · 12-08-2009, 01:05 PM

Quote:

Originally Posted by SS Mike

Thats weird, that size is close enough to the same size. Your 18's have an OD of 28.6299 vs. the 20's 28.6614, so it's actually barely smaller, but i wouldnt think that would make that much of a difference. Not sure why that's happening.

I agree, there is no difference in the tires at all. The original tires will wear out and be even smaller than the 18s that are on now.....

non issue

CamaroBAMF28 · 12-08-2009, 01:10 PM

Quote:

Originally Posted by ChevyBoiler

I know this has been discussed in some other threads, but I have some actual data now that I have put my winter tires on, and the results are not what I hoped for.

I have a 2LT RS that came with the 20" rims and Pirellis. I replaced those with 18" rims and 225/60R18 Goodyear UltraGrips for the winter. This combination should have the same Outer Diameter as the 20" rims with 245/45R20 tires, so I would have expected the odometer/speedometer to not be afftected. I took it for a test drive the other day and found that my odometer calibration is incorrect. Using the milemarkers on the interstate, found that I am registering 5.0 miles traveled by the time I reach 4.7 miles by the milemarkers, so my odometer is now gaining a little over 0.3 miles for every 5.0 miles I travel. This is likely throwing off my speedometer as well, but I haven't been able to test that (can't wait to use that excuse when I get pulled over).

Anyway, just wondering if anyone else is finding similar results and what the possible solutions may be?

im ordering winter tires too and im trying to find 20's just so i dont have that problem. but the winter tires for the 20 inch rims are so expensive on tirerack!

12-06-2009, 07:53 PM	#1
ChevyBoiler Drives: 2010 Camaro 2LT RS Join Date: Feb 2009 Location: Indianapolis Posts: 8	Rim Size and Odometer Calibration I know this has been discussed in some other threads, but I have some actual data now that I have put my winter tires on, and the results are not what I hoped for. I have a 2LT RS that came with the 20" rims and Pirellis. I replaced those with 18" rims and 225/60R18 Goodyear UltraGrips for the winter. This combination should have the same Outer Diameter as the 20" rims with 245/45R20 tires, so I would have expected the odometer/speedometer to not be afftected. I took it for a test drive the other day and found that my odometer calibration is incorrect. Using the milemarkers on the interstate, found that I am registering 5.0 miles traveled by the time I reach 4.7 miles by the milemarkers, so my odometer is now gaining a little over 0.3 miles for every 5.0 miles I travel. This is likely throwing off my speedometer as well, but I haven't been able to test that (can't wait to use that excuse when I get pulled over). Anyway, just wondering if anyone else is finding similar results and what the possible solutions may be? __________________ 1st Car - 1990 Chevrolet Cavalier - Dark Blue 2nd Car - 1995 Chevrolet Camaro - Mystic Teal 3rd Car - 2004 Chevrolet Monte Carlo SS - IBM Current - 2010 Chevrolet Camaro 2LT - CGM

12-06-2009, 11:23 PM	#2
SS Mike Drives: 2010 Camaro SS/RS CGM M6 Join Date: Jun 2009 Location: Orange County, California Posts: 804	Thats weird, that size is close enough to the same size. Your 18's have an OD of 28.6299 vs. the 20's 28.6614, so it's actually barely smaller, but i wouldnt think that would make that much of a difference. Not sure why that's happening. __________________ Vortech V-3 Kit, ARH LT's, Custom Exhaust, Aeromotive A1000 Fuel System, Custom Tune - 582 rwhp 533 rwtq 22" Modulare H2 Wheels, CF Hood, Trunk, Spoiler & Roof by Carbon by Design, Custom Steering Wheel from P-Factor Brembo GT BBK, Alpine INA-900, Alpine Type-R Speakers, Hurst Shifter, APR Splitter, Custom Quad Tip Diffuser CKS C1 Coilovers, Falken 452 Tires, 265/35/22 & 285/35/22, Custom Grille, AAC Halos, and much more to come!!

12-08-2009, 01:12 AM	#4
d69chris Florida C5 Drives: 2010 Camaro 2SS Vortech L99 IOM Join Date: Jul 2009 Location: Tequesta, FL Posts: 2,608 View My Garage	I would not always believe the mile markers, maybe use a tape measure..... __________________ Ordered 11/08/08....Del. 08/05/2009 Loving every minute of it! Don't hate me because i'm Pretty....

12-08-2009, 11:33 AM	#6
Sir Nuke Master of All Things Drives: '26 Corvette Stingray Join Date: Jul 2009 Location: Southeast of Houston, Texas Posts: 22,680 View My Garage	I would never trust the markers.......and I believe the odometer and the speedo are linked. so if one is off, the other will be too........and since your new tires are that close, there is no way that your odometer/speedo is off that much. __________________

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