ElpiAuto305/55R20 vs 315/60R20
315/60R20 is 1.67″ (42 mm) taller than 305/55R20, a 5.0% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
| Measurement | 305/55R20 | 315/60R20 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 33.21″ | 34.88″ | +1.67″ | +5.0% |
| Section width | 12.01″ | 12.40″ | +0.39″ | +3.3% |
| Sidewall height | 6.60″ | 7.44″ | +0.84″ | +12.7% |
| Circumference | 104.33″ | 109.58″ | +5.26″ | +5.0% |
| Revs per mile | 607.3 | 578.2 | −29.1 | −4.8% |
| Revs per km | 377.4 | 359.3 | −18.1 | −4.8% |
Speedometer: with 305/55R20 as the original, 315/60R20 makes an indicated 60 mph really about 63.0 mph, and the axle sits ~0.84″ higher.
Reading this comparison
The overall diameter is what matters here: 315/60R20 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.