Might be a stupid ? but I don't know the answer. Do I need to change my gears do to the fact that I am running 20" rims with 295/40/20 in the rear and 255/40/20 in the front?
New gears?
- Thread starter DexwarL
- Start date
When you increase the heighth of your tire you decrease your rear axle ratio. So if you changed from your stock wheels and tires (28" tall) and let's say went to a 32" tall (20"rim and tire) you have changed your ratio from a stock 3.55(stock '99 gear) to approx. a 3.10 ratio. It is measured by run out of the tire or what we call the circumference. It is figured by multiplying the height of the tire x 3.14. Example: Stock height would be 28" x 3.14 = 87.92" circumference (stock)
New height would be 32" x 3.14 = 100.48" circumference
Always divide the stock circumference by the new circumference. This gives you the % of change.
Multiply your % of change x your stock gear ratio and it gives you your new ratio. 87.92 divided by 100.48 = 87.5% x 3.55 = 3.10
If you shorten the height your gear ratio will go the other way, using the same formula. Hope this helps.
New height would be 32" x 3.14 = 100.48" circumference
Always divide the stock circumference by the new circumference. This gives you the % of change.
Multiply your % of change x your stock gear ratio and it gives you your new ratio. 87.92 divided by 100.48 = 87.5% x 3.55 = 3.10
If you shorten the height your gear ratio will go the other way, using the same formula. Hope this helps.
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