ElpiAuto275/55R20 vs 305/55R20
305/55R20 is 1.30″ (33 mm) taller than 275/55R20, a 4.1% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
| Measurement | 275/55R20 | 305/55R20 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 31.91″ | 33.21″ | +1.30″ | +4.1% |
| Section width | 10.83″ | 12.01″ | +1.18″ | +10.9% |
| Sidewall height | 5.95″ | 6.60″ | +0.65″ | +10.9% |
| Circumference | 100.25″ | 104.33″ | +4.08″ | +4.1% |
| Revs per mile | 632.0 | 607.3 | −24.7 | −3.9% |
| Revs per km | 392.7 | 377.4 | −15.4 | −3.9% |
Speedometer: with 275/55R20 as the original, 305/55R20 makes an indicated 60 mph really about 62.4 mph, and the axle sits ~0.65″ higher.
Reading this comparison
The overall diameter is what matters here: 305/55R20 is the taller tire. It sets ride height, gearing and how far the tire travels per revolution — which is what the speedometer and odometer count. Width and sidewall change fit and feel (a wider tire needs a wider wheel and more clearance; a shorter sidewall sharpens steering) but not the gearing.
Figures are geometric estimates from the size codes; real moulded tires vary by brand by 1–3%. Confirm load rating, wheel width and physical clearance on your vehicle before fitting. To compare any other two sizes, use the tire size comparison tool; to decode one size and see what else fits its wheel, the tire size calculator.