How does Tire width affect wheel speed/speedometer?
Thread Starter
Teching In
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From: Tampa, Florida
How does Tire width affect wheel speed/speedometer? On my 97 RS Camaro, originally had 235/55-16. Since then I've thrown on my spare Zr1 wheels with 275/40-17's.
According to Tire Size calculators, that would throw my speedo off by roughly 2%
Now for the question; Would going down on my 275's to 245/40-17 affect the speedo? According to tire size calculators that throws it off even further with another 3% off up to ~6% from the 235/55-16's.
Does changing the tire width really affect it that much?
According to Tire Size calculators, that would throw my speedo off by roughly 2%
Now for the question; Would going down on my 275's to 245/40-17 affect the speedo? According to tire size calculators that throws it off even further with another 3% off up to ~6% from the 235/55-16's.
Does changing the tire width really affect it that much?
It's not about width, its about outside diameter or circumference. Check this site for a nice calculator that shows diameter and circumference. I see 26.2 vs 25.7 (275s) diameter.
https://tiresize.com/calculator/
https://tiresize.com/calculator/
The 2nd number is percentage of the width that is the sidewall. So tire #1 at 275/40 has a 110mm sidewall and tire #2 at 245/40 has a 98mm sidewall. To have the same height of tire, tire #2 would need to be 245/45 which is 110.25mm so pretty darn close.
Remember, the total diameter of the tire includes the sidewall twice (sidewall, wheel, sidewall).
Yes, tire sizes mix standard and metric. Wheel size is in inches, width is in millimeters. Probably just to confuse the issue.
Remember, the total diameter of the tire includes the sidewall twice (sidewall, wheel, sidewall).
Yes, tire sizes mix standard and metric. Wheel size is in inches, width is in millimeters. Probably just to confuse the issue.
Last edited by SparkyJJO; Mar 7, 2016 at 12:39 PM.
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From: Maricopa, AZ
The 2nd number is percentage of the width that is the sidewall. So tire #1 at 275/40 has a 110mm sidewall and tire #2 at 245/40 has a 98mm sidewall. To have the same height of tire, tire #2 would need to be 245/45 which is 110.25mm so pretty darn close.
Remember, the total diameter of the tire includes the sidewall twice (sidewall, wheel sidewall).
Yes, tire sizes mix standard and metric. Wheel size is in inches, width is in millimeters. Probably just to confuse the issue.
Remember, the total diameter of the tire includes the sidewall twice (sidewall, wheel sidewall).
Yes, tire sizes mix standard and metric. Wheel size is in inches, width is in millimeters. Probably just to confuse the issue.
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
As explained above, simply adding width at the same aspect ratio ("second" number in the tire size) will cause the tire to be taller due to the greater percentage of sidewall. You'd have to lower that ratio/percentage (or wheel diameter) to get a wider tire to have the same overall diameter.
Thread Starter
Teching In
Joined: Nov 2014
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From: Tampa, Florida
Sweet, Thanks everyone.
I was not aware that the second number was a percentage of the first, which explains a lot.
Edit: Probably wrong section, but would tuning the speedo be easy to do if it's just tire size?
I was not aware that the second number was a percentage of the first, which explains a lot.
Edit: Probably wrong section, but would tuning the speedo be easy to do if it's just tire size?
Last edited by Tehk302; Mar 8, 2016 at 12:37 PM.
