Tire & wheel tools
Tire and gear ratio calculator
Enter the factory tire, the new tire and the factory axle ratio to see the effective ratio after the swap — and the theoretical ratio that would restore the original feel.
Effective ratio after swap
2.85 : 1
Diameter change +30.98%
Restoring the original feel would theoretically need a 4.89 : 1 gear (diameter +30.98%).
Old 225/45R17 · ⌀634.3 mmNew 285/70R17 · ⌀830.8 mm
| Factory axle ratio | 3.73 : 1 |
|---|---|
| Effective ratio | 2.85 : 1 |
| Ratio to restore | 4.89 : 1 |
| Diameter change | +30.98% |
Computed on theoretical diameters only — rolling radius, gearbox ratios and the discrete ratios actually sold are out of scope. Use it for direction, not for ordering parts.
How it is calculated
Effective ratio = factory ratio × old diameter ÷ new diameter; ratio to restore = factory ratio × new diameter ÷ old diameter.
A taller tire raises speed per wheel revolution and cuts wheel torque — equivalent to fitting a shorter (numerically lower) gear: duller launches and hill climbs, higher theoretical top speed. The back-computed ratio restores wheel-end behavior in theory; only the ratios actually sold are available.
How to fill each field
- Factory ratioFrom the spec sheet or the axle tag — typically 3.2–4.6. Single-speed EV reducers work the same way.
- Effective ratioThe ratio the swap behaves like. Lower than stock means each engine/motor rpm maps to a higher road speed.
- Ratio to restoreThe theoretical target. Real axle gears come in discrete steps — pick the nearest, which may not restore it fully.
FAQ
Why does a taller tire feel sluggish?
A bigger diameter covers more road per wheel revolution, lengthening the whole driveline ratio. Wheel torque drops in inverse proportion — softer launches and hills.
How much does a 4.10 turning effectively into 3.7 matter?
About 10% less wheel torque and 10% more speed per rpm. Restoring factory feel would theoretically need 4.10 × new diameter ÷ old diameter.
What if the required ratio is not sold?
Axle gears come in discrete options — take the nearest one, or pick a slightly shorter tire to close the gap from the other side.
Does this apply to EVs?
The math is the same for single-speed reducers: a diameter change scales road speed and wheel torque together, but the ratio cannot be swapped — tire size is the only lever.