Gear ratio calculator (tire size change)
How does tire size affect gear ratio?
A taller tire lowers your effective final-drive ratio: the engine turns fewer times per kilometre, so acceleration softens and cruising RPM drops. The effective ratio equals your axle ratio × old diameter ÷ new diameter. To restore stock drivability after fitting taller tires, re-gear to a numerically higher axle ratio.
- Effective ratio now
- 3.60
- Effective ratio change
- -3.4%
- Re-gear to restore stock
- 3.90
Top-gear estimate from tire diameter; actual RPM also depends on transmission gearing.
Detailed reference pages
Choose a common value or size to open its calculated data and explanation.