Tire gear ratio calculator
Enter the original tire A, replacement B and current final-drive ratio to see the gearing effect and the ratio that would restore it.
Example settings — replace these with your own.
Enter a full metric or flotation code. XL, C and load/speed markings are accepted.
All results use A as the original calibration and B as the replacement.
Equivalent gearing relative to tire A, using the current final-drive ratio with tire B.
Theoretical final-drive ratio for tire B that preserves the original gearing with A.
- A · Diameter
- 32.99 in83.80 cm
- B · Diameter
- 33.46 in85.00 cm
- Circumference ratio B ÷ A
- 1.014320
Uses the same transmission gear. Compare the calculated restoring ratio with available final-drive gear sets.
How the calculation works
r = circumference B ÷ circumference A = diameter B ÷ diameter A
Effective ratio = current final-drive ratio ÷ r
Restoring ratio = current final-drive ratio × r
Worked example
A: 275/60R20 (838 mm) → B: 285/60R20 (850 mm).
r = 850 ÷ 838 = 1.014320
Effective ratio with B: 4.10 ÷ 1.014320 ≈ 4.042:1
Ratio to restore the original gearing: 4.10 × 1.014320 ≈ 4.159:1
Inputs and assumptions
Dimensions come from the nominal size code. Model, wear, load and pressure affect the actual rolling circumference.
The size portion supplies the geometry. XL/C and load/speed markings stay in shared links. Check service ratings against the vehicle placard and exact tire model.
Method and data