33x12.50R15 to 35x12.50R17 gear ratio change
Effective ratio after tire change
Changing from 33x12.50R15 to 35x12.50R17 makes a 3.73 axle behave like 3.52. To restore the original cruise RPM and drivability, the math points toward about 3.96; verify real ratios, transmission gearing and vehicle limits before buying parts.
| Original size | New size | Diameter delta | Reference axle ratio | Effective ratio after tire change | Target ratio to restore RPM |
|---|---|---|---|---|---|
| 33x12.50R15 33.00 in | 35x12.50R17 35.00 in | +6.06% | 3.73 | 3.52 | 3.96 |
| Nearest standard axle ratio | Cruise RPM at 100 km/h (62 mph) | Size verdict |
|---|---|---|
| 3.90 | 2361 → 2226 RPM | Outside diameter tolerance |
Gear-ratio seed pages use the public TireFitLab size corpus and a fixed 3.73 reference axle so the math is comparable. They are drivetrain estimates, not vehicle-specific fitment advice.
RPM assumes top gear is 1:1. Overdrive transmissions, torque-converter slip and final-drive variants change real vehicle RPM.
How tire diameter changes gearing
Taller tires cover more distance per wheel revolution, so the engine turns fewer times per kilometre with the same axle ratio. Shorter tires do the opposite. The effective ratio expresses that change as if the axle gearing had been altered without opening the differential.
Related drivetrain references
Seasonal check
Planning a long summer drive?
Use the budget and running-cost tools before a trip, especially if the current tires are worn or the replacement size changes diameter.
- Technical check
- 2026-06-28
- Content updated
- 2026-06-28
What changed
- Added curated gear-ratio change seed pages from deterministic tire geometry.