275/55R20 vs 265/60R18 Side-by-side tire size comparison with specs and compatibility
This tire swap is between 3-5% diameter difference. Check for fender clearance and be aware of speedometer error. May require recalibration.
Full Specifications Comparison
| Specification | 275/55R20 | 265/60R18 | Difference |
|---|---|---|---|
| Overall Diameter | 810.5 mm (31.9") | 775.2 mm (30.5") | -35.3 mm |
| Section Width | 275 mm (10.8") | 265 mm (10.4") | -10 mm |
| Sidewall Height | 151.3 mm | 159 mm | +7.7 mm |
| Circumference | 2546.3 mm | 2435.4 mm | -110.9 mm |
| Revolutions/Mile | 632 | 661 | +29 |
| Aspect Ratio | 55% | 60% | +5% |
| Rim Diameter | 20" | 18" | -2" |
Key Impact Summary
Speedometer Correction Table
When switching from 275/55R20 to 265/60R18, your speedometer will over-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 28.7 mph | -1.3 mph |
| 40 mph | 38.3 mph | -1.7 mph |
| 50 mph | 47.8 mph | -2.2 mph |
| 60 mph | 57.4 mph | -2.6 mph |
| 70 mph | 67 mph | -3 mph |
| 80 mph | 76.5 mph | -3.5 mph |
| 90 mph | 86.1 mph | -3.9 mph |
| 100 mph | 95.6 mph | -4.4 mph |
| 110 mph | 105.2 mph | -4.8 mph |
| 120 mph | 114.8 mph | -5.2 mph |
What This Swap Means
Narrower tires (265/60R18): The 10mm narrower contact patch reduces rolling resistance, potentially improving fuel economy. Narrower tires also cut through standing water better, reducing hydroplaning risk. However, dry grip and cornering stability may decrease slightly.
Taller sidewall: The 7.7mm 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: Decreases by 17.6mm, lowering the center of gravity slightly which can improve handling stability.