ElpiAuto285/50R20 vs 305/50R20
305/50R20 is 0.79″ (20 mm) taller than 285/50R20, a 2.5% difference in overall diameter — right at the edge of the ±3% band — fine on most cars, but check clearance at full lock and full suspension compression.
| Measurement | 285/50R20 | 305/50R20 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 31.22″ | 32.01″ | +0.79″ | +2.5% |
| Section width | 11.22″ | 12.01″ | +0.79″ | +7.0% |
| Sidewall height | 5.61″ | 6.00″ | +0.39″ | +7.0% |
| Circumference | 98.08″ | 100.56″ | +2.47″ | +2.5% |
| Revs per mile | 646.0 | 630.1 | −15.9 | −2.5% |
| Revs per km | 401.4 | 391.5 | −9.9 | −2.5% |
Speedometer: with 285/50R20 as the original, 305/50R20 makes an indicated 60 mph really about 61.5 mph, and the axle sits ~0.39″ higher.
Reading this comparison
The overall diameter is what matters here: 305/50R20 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.