If Tire Diameter Increases By 2", What Rear Gear?

If I install tires that are 2" in diameter larger, what rear end gear ratio would I then need to compensate? Is there a formula for this calculation? Thanks

Circumference of old tire divided by new tire will tell you how much the gearing changes. Multiply that by your current gear ratio and it should decrease in size.

If you want the same affective ratio then just find the percentage change in inches of tire height and apply that percentage to the gear ratio.

Hahaha Greg we said the same thing :thumb:

I know, I'm a nerd. Circumference is more accurate than diameter.

yeah with the weight acting on the sidewall the tire isn't round.

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Originally Posted by RedHeartbeat

Circumference of old tire divided by new tire will tell you how much the gearing changes. Multiply that by your current gear ratio and it should decrease in size.

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Dang! That actually works! LOL...:) Thanks

rule of thumb is for every inch you go up or down you gain or lose .010 of gear

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Originally Posted by Quik

rule of thumb is for every inch you go up or down you gain or lose .010 of gear

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So if I've got 3.42's with a 29" tire and go to a 26" DR, my ratio would be a 3.45?? Do you mean .10 of gear? That would be a 3.72.

I'm to lazy for all of that here's a good site to http://www.miata.net/garage/tirecalc.htmlhelp out

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Originally Posted by ramair2002

So if I've got 3.42's with a 29" tire and go to a 26" DR, my ratio would be a 3.45?? Do you mean .10 of gear? That would be a 3.72.

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yes your are right, i had wrong decimal point