Gear ratio calculator (tyre size change)
How does tyre size affect gear ratio?
A taller tyre 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 tyres, 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 tyre diameter; actual RPM also depends on transmission gearing.
More tools
- Revs per mile / km calculator
- Plus sizing guide
- Speedometer error calculator
- Tire size calculator
- Tire & wheel reference guides
What changed
- Reviewed deterministic geometry, load/speed references, sitemap inclusion and localized page shell.