285/55R20 vs 305/55R20 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 | 285/55R20 | 305/55R20 | Difference |
|---|---|---|---|
| Overall Diameter | 821.5 mm (32.3") | 843.5 mm (33.2") | +22 mm |
| Section Width | 285 mm (11.2") | 305 mm (12") | +20 mm |
| Sidewall Height | 156.8 mm | 167.8 mm | +11 mm |
| Circumference | 2580.8 mm | 2649.9 mm | +69.1 mm |
| Revolutions/Mile | 624 | 607 | -17 |
| Aspect Ratio | 55% | 55% | 0% |
| Rim Diameter | 20" | 20" | 0" |
Key Impact Summary
Speedometer Correction Table
When switching from 285/55R20 to 305/55R20, your speedometer will under-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 mph |
| 40 mph | 41.1 mph | +1.1 mph |
| 50 mph | 51.3 mph | +1.3 mph |
| 60 mph | 61.6 mph | +1.6 mph |
| 70 mph | 71.9 mph | +1.9 mph |
| 80 mph | 82.1 mph | +2.1 mph |
| 90 mph | 92.4 mph | +2.4 mph |
| 100 mph | 102.7 mph | +2.7 mph |
| 110 mph | 112.9 mph | +2.9 mph |
| 120 mph | 123.2 mph | +3.2 mph |
What This Swap Means
Wider tires (305/55R20): The 20mm 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 11.0mm 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 11mm, providing slightly better approach angles for off-road driving and speed bump clearance.