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Old October 25th, 2006, 09:27
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Roxtar Roxtar is offline
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What gear ratio do I want?

Deciding what gear ratio to use when changing tire size is actually quite simple.
It's just a matter of mathematics.

Current tire size/new tire size =current gear ratio/new gear ratio

This simple formula will allow you to figure out what ratio will get you back to your current performance.
For instance, let's say you have stock 3.55 gears & stock tires and want to go to 33" tires.
Stock XJ tires are about 27" tall so:

27/33 = 3.55/new gear ratio

Cross multiplying (thought you'd never use algebra again?) gets you this:
33 X 3.55 = 27 X new gear ratio

117.15 = 27 X new gear ratio

117.15/27 = 4.34

IOW, 4.56 gears (the closest avail to 4.34) will give you slightly lower gearing than you had while stock.
From here it's up to you where to go.
If stock performance is fine stay with 4.56. If you want a little more low end grunt, go to 4.88. If you want to murder the rocks go to 5.13 or lower.
BTW, lower gears = higher numerically.

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