ElpiAuto305/50R20 vs 35X12.50R20
35X12.50R20 is 2.99″ (76 mm) taller than 305/50R20, a 9.3% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
| Measurement | 305/50R20 | 35X12.50R20 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 32.01″ | 35.00″ | +2.99″ | +9.3% |
| Section width | 12.01″ | 12.50″ | +0.49″ | +4.1% |
| Sidewall height | 6.00″ | 7.50″ | +1.50″ | +24.9% |
| Circumference | 100.56″ | 109.96″ | +9.40″ | +9.3% |
| Revs per mile | 630.1 | 576.2 | −53.9 | −8.5% |
| Revs per km | 391.5 | 358.1 | −33.5 | −8.5% |
Speedometer: with 305/50R20 as the original, 35X12.50R20 makes an indicated 60 mph really about 65.6 mph, and the axle sits ~1.50″ higher.
Reading this comparison
The overall diameter is what matters here: 35X12.50R20 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.