Re-gear calculator for bigger tires
Bigger tires make your axle ratio act lower. Enter your tire sizes and axle ratio to see the effective ratio, the ratio that restores stock engine speed, and the RPM at highway speed.
| Effective axle ratio with new tires | 3.60 | was 3.73 |
|---|---|---|
| Axle ratio to restore stock RPM | 3.86 | |
| Engine RPM at 65 mph, stock tires | 2,578 | |
| Engine RPM at 65 mph, new tires | 2,492 | −86 rpm |
| With 4.10 axle and new tires | 2,739 | +6.2% vs stock gearing |
The formulas
- Effective axle ratio = axle ratio × old tire diameter ÷ new tire diameter.
- Ratio to restore stock engine speed = axle ratio × new tire diameter ÷ old tire diameter.
- Engine RPM = mph × axle ratio × top gear ratio × 336.13 ÷ tire diameter (in). The constant is 63,360 inches in a mile ÷ (60 minutes × π).
Tire diameters are nominal, from the official sizing formula. A real tire is a little smaller under load, so measured RPM can be slightly higher. Axle ratios are sold in fixed steps that depend on the axle; pick the available ratio closest to the "ratio to restore" value, and check with the axle or gear maker.
What re-gearing changes
A taller tire lowers engine RPM at a given speed and makes the speedometer read low (see changing tire size). A numerically higher axle ratio brings the RPM back. The speedometer still needs recalibrating after a tire size change, whether or not you change the gears.
Printed from https://tiresizecalc.net/regear-calculator/. Figures as published on 2026-11-01. The full working and the official sources are on that page.
Sources
- UN Regulation No. 30 - Uniform provisions concerning the approval of pneumatic tyres for motor vehicles and their trailers (Revision 3). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.29/Rev.3. 2007-03-29. Para 6.1.2.1: tire outer diameter. Retrieved 2026-11-01.
- UN Regulation No. 54 - Uniform provisions concerning the approval of pneumatic tyres for commercial vehicles and their trailers (Revision 2). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.53/Rev.2. 2004-04-16. Para 6.1.2.1 and Annex 5 Table B: light truck and inch tire diameters. Retrieved 2026-11-01.
- Computed by tiresizecalc.net from the cited formula. Sri Murugan Systems. Effective ratio = axle x old diameter / new diameter; RPM = mph x axle x gear x 63,360 / (60 x pi x diameter). Retrieved 2026-11-01.
Last reviewed 2026-11-01. The full source list, with dates and file checksums, is in How the numbers are calculated. To report an error, email contactus@tiresizecalc.net.