What size tire for a 18 x 8.5" wheel?
12-03-2006, 11:18 AM
#1
AudiWorld Senior Member
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What size tire for a 18 x 8.5" wheel?
Or better yet, could someone teach me how to figure out what size tires fit a given wheel? I've always struggled with this.
12-06-2006, 01:02 PM
#4
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How to calculate wheel diameter...
To calculate the diameter of the wheel/tire combination, use this formula:
wheel width(mm) x ratio% x 2 / 25.4 + wheel diameter(in)
For example:
A tire size of 225/40R18 would be:
225 x 0.40 x 2 / 25.4 + 18 = 25.09" diameter
The 245/35R18 would be:
245 x 0.35 x 2 / 25.4 + 18 = 24.75" diameter
I generally try to keep the tire/wheel combo within a 0.5" diameter of the OE tire/wheel combo size to keep the speedo and odometer as accurate as possible. If you exceed that on the positive side you will want to make sure the added diameter will not cause rubbing issues and probably have your speedo recalibrated.
I also like this web link.<ul><li><a href="http://www.1010tires.com/TireSizeCalculator.asp">Tire Size Calculator</a></li></ul>
wheel width(mm) x ratio% x 2 / 25.4 + wheel diameter(in)
For example:
A tire size of 225/40R18 would be:
225 x 0.40 x 2 / 25.4 + 18 = 25.09" diameter
The 245/35R18 would be:
245 x 0.35 x 2 / 25.4 + 18 = 24.75" diameter
I generally try to keep the tire/wheel combo within a 0.5" diameter of the OE tire/wheel combo size to keep the speedo and odometer as accurate as possible. If you exceed that on the positive side you will want to make sure the added diameter will not cause rubbing issues and probably have your speedo recalibrated.
I also like this web link.<ul><li><a href="http://www.1010tires.com/TireSizeCalculator.asp">Tire Size Calculator</a></li></ul>
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