Gear Ratio and Tire Size Calculator
Determine your vehicle's effective gear ratio and engine RPM change after installing larger or smaller tires.
Quick Answer
If your truck came with 31-inch tires and a 3.73 factory gear ratio, upgrading to 35-inch tires will drop your effective gear ratio to 3.30. To return your truck's acceleration and RPMs back to factory spec, you would need to install new 4.10 or 4.11 axle gears.
Sizes:
Recommended Gear Ratios by Tire Size (at 65 mph)
| Tire Diameter | Highway (~2000 RPM) | All-Around (~2300 RPM) | Towing (~2600 RPM) |
|---|---|---|---|
| 31" | 3.55 | 3.73 | 4.10 |
| 33" | 3.73 | 4.10 | 4.56 |
| 35" | 4.10 | 4.56 | 4.88 |
| 37" | 4.56 | 4.88 | 5.13 |
| 40" | 4.88 | 5.13 | 5.38 |
Formula
New Gear Ratio = (New Tire Diameter / Old Tire Diameter) × Old Gear Ratio
- New Tire Diameter = overall height of upgraded tire in inches
- Old Tire Diameter = overall height of factory tire in inches
- Old Gear Ratio = factory axle ring and pinion ratio
- Example: (35 / 31) × 3.73 = 4.21 → round to nearest available gear set (4.10 or 4.56)