QuickCheckToolsTire size calculator › 275/55R20 vs 33x12.50R20
275/55R20 vs 33x12.50R20
33x12.50R20 is 1.1 inches (3.4%) taller than 275/55R20 and 1.7 inches wider. Ground clearance changes by about 0.5 inches, and at an indicated 60 mph you would actually be doing 62.1 mph.
33x12.50R20 is 3.4% taller
That's more than the usual 3% guideline, so check clearance, and expect speedometer, ABS and gearing to be affected.
| 275/55R20 | 33x12.50R20 | Difference | |
|---|---|---|---|
| Overall diameter | 31.9 in | 33.0 in | +1.1 in |
| Width | 10.8 in | 12.5 in | +1.7 in |
| Sidewall height | 6.0 in | 6.5 in | +0.5 in |
| Circumference | 100.2 in | 103.7 in | +3.4 in |
| Revolutions per mile | 632 | 611 | -21 |
Speedometer with 33x12.50R20 fitted (calibrated for 275/55R20)
| Speedometer shows | Actual speed |
|---|---|
| 20 mph | 20.7 mph |
| 30 mph | 31.0 mph |
| 40 mph | 41.4 mph |
| 50 mph | 51.7 mph |
| 60 mph | 62.1 mph |
| 70 mph | 72.4 mph |
| 80 mph | 82.7 mph |
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What the difference means
Diameter is what matters most. A taller tire raises the vehicle by half the difference, here about 0.5 inches, and covers more ground per turn, so the speedometer reads lower than your real speed. Width changes how much tread meets the road and whether the tire clears suspension parts and wheel arches.
These are design dimensions calculated from the sizes. Actual tires vary slightly by brand and model, so check fitment for your vehicle before buying.