ElpiAuto30X9.50R15 vs 31X10.50R15
31X10.50R15 is 1.00″ (25 mm) taller than 30X9.50R15, a 3.3% difference in overall diameter — outside the ±3% band, so expect the speedometer to drift and check for rubbing before fitting.
| Measurement | 30X9.50R15 | 31X10.50R15 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 30.00″ | 31.00″ | +1.00″ | +3.3% |
| Section width | 9.50″ | 10.50″ | +1.00″ | +10.5% |
| Sidewall height | 7.50″ | 8.00″ | +0.50″ | +6.7% |
| Circumference | 94.25″ | 97.39″ | +3.14″ | +3.3% |
| Revs per mile | 672.3 | 650.6 | −21.7 | −3.2% |
| Revs per km | 417.7 | 404.3 | −13.5 | −3.2% |
Speedometer: with 30X9.50R15 as the original, 31X10.50R15 makes an indicated 60 mph really about 62.0 mph, and the axle sits ~0.50″ higher.
Reading this comparison
The overall diameter is what matters here: 31X10.50R15 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.