Calculator
Shop truck & LT tires Speedometer & Gear Ratio Calculator
Sizing up to a taller truck or off-road tire? See exactly how far off your speedometer and odometer will read, and what axle ratio restores your factory gearing.
Speedometer & gear ratio
Going up in tire size makes your speedometer and odometer read low. Enter both sizes to see by how much — and what axle ratio puts your gearing back where the factory had it.
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31.61" overall32.71" overall(+3.5%)
At an indicated 60 mph you're actually doing 62.1 mph (+2.1 mph off)
Your odometer will under-count miles by about 3.4%.
To keep the same effective gearing, re-gear to about 3.67:1 (from 3.55:1).
Based on nominal sidewall math — real mounted diameter varies a little by brand and inflation pressure.