235/55R20 vs 255/50R20 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 | 235/55R20 | 255/50R20 | Difference |
|---|---|---|---|
| Overall Diameter | 766.5 mm (30.2") | 763 mm (30") | -3.5 mm |
| Section Width | 235 mm (9.3") | 255 mm (10") | +20 mm |
| Sidewall Height | 129.3 mm | 127.5 mm | -1.8 mm |
| Circumference | 2408 mm | 2397 mm | -11 mm |
| Revolutions/Mile | 668 | 671 | +3 |
| Aspect Ratio | 55% | 50% | -5% |
| Rim Diameter | 20" | 20" | 0" |
Key Impact Summary
Speedometer Correction Table
When switching from 235/55R20 to 255/50R20, your speedometer will over-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 29.9 mph | -0.1 mph |
| 40 mph | 39.8 mph | -0.2 mph |
| 50 mph | 49.8 mph | -0.2 mph |
| 60 mph | 59.7 mph | -0.3 mph |
| 70 mph | 69.7 mph | -0.3 mph |
| 80 mph | 79.6 mph | -0.4 mph |
| 90 mph | 89.6 mph | -0.4 mph |
| 100 mph | 99.5 mph | -0.5 mph |
| 110 mph | 109.5 mph | -0.5 mph |
| 120 mph | 119.5 mph | -0.5 mph |
What This Swap Means
Wider tires (255/50R20): 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.
Shorter sidewall: The 1.8mm decrease in sidewall height improves steering response and cornering precision. However, ride quality becomes firmer and the wheels are more vulnerable to pothole damage. This is a common trade-off when upsizing wheels (plus-sizing).
Ground clearance: Decreases by 1.7mm, lowering the center of gravity slightly which can improve handling stability.