245/40R20 vs 255/40R20 Side-by-side tire size comparison with specs and compatibility
This tire swap is within the safe 3% diameter threshold. It should not cause issues with speedometer accuracy, ABS, or traction control systems.
Full Specifications Comparison
| Specification | 245/40R20 | 255/40R20 | Difference |
|---|---|---|---|
| Overall Diameter | 704 mm (27.7") | 712 mm (28") | +8 mm |
| Section Width | 245 mm (9.6") | 255 mm (10") | +10 mm |
| Sidewall Height | 98 mm | 102 mm | +4 mm |
| Circumference | 2211.7 mm | 2236.8 mm | +25.1 mm |
| Revolutions/Mile | 728 | 719 | -9 |
| Aspect Ratio | 40% | 40% | 0% |
| Rim Diameter | 20" | 20" | 0" |
Key Impact Summary
Speedometer Correction Table
When switching from 245/40R20 to 255/40R20, your speedometer will under-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 mph |
| 40 mph | 40.5 mph | +0.5 mph |
| 50 mph | 50.6 mph | +0.6 mph |
| 60 mph | 60.7 mph | +0.7 mph |
| 70 mph | 70.8 mph | +0.8 mph |
| 80 mph | 80.9 mph | +0.9 mph |
| 90 mph | 91 mph | +1 mph |
| 100 mph | 101.1 mph | +1.1 mph |
| 110 mph | 111.3 mph | +1.3 mph |
| 120 mph | 121.4 mph | +1.4 mph |
What This Swap Means
Wider tires (255/40R20): The 10mm wider contact patch provides better grip in dry conditions and improved cornering stability. However, wider tires increase rolling resistance slightly, which may affect fuel economy by 1-2%. They are also more susceptible to hydroplaning in wet conditions.
Taller sidewall: The 4.0mm increase in sidewall height provides a more comfortable ride by absorbing more road imperfections. Taller sidewalls also offer better protection against pothole damage to wheels. The trade-off is slightly less responsive steering feel.
Ground clearance: Increases by 4mm, providing slightly better approach angles for off-road driving and speed bump clearance.