30x9.50R15 vs 31x10.50R15
31x10.50R15 is outside the ±3% rule as a replacement for 30x9.50R15: the diameter differs by +3.33%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Side by side
| 30x9.50R15 | 31x10.50R15 | Difference | |
|---|---|---|---|
| Overall diameter | 30.00" | 31.00" | +1.00" (+3.33%) |
| Section width | 241 mm | 267 mm | +26 mm |
| Sidewall | 7.50" | 8.00" | +0.50" |
| Rim | 15" | 15" | same |
| Circumference | 94.2" | 97.4" | +3.1" |
| Revs per mile | 672 | 651 | -22 |
| Ride height | — | — | +0.50" |
| Speedometer reads 60 mph | 60.0 | 62.0 | +2.0 mph |
Speedometer and odometer
With 31x10.50R15 on a car calibrated for 30x9.50R15, the speedometer reads 58.1 mph when you're really doing 60, and the odometer under-counts by 3.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.0 mph |
| 45 mph | 46.5 mph |
| 60 mph | 62.0 mph |
| 70 mph | 72.3 mph |
| 80 mph | 82.7 mph |
Other sizes close to 30x9.50R15
Questions
Can I replace 30x9.50R15 with 31x10.50R15?
31x10.50R15 is outside the ±3% rule as a replacement for 30x9.50R15: the diameter differs by +3.33%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 30x9.50R15 and 31x10.50R15?
31x10.50R15 is 1.00" taller and 26 mm wider; the sidewall is +0.50". At an indicated 60 mph you'd actually be doing 62.0 mph.
Will 31x10.50R15 fit on 30x9.50R15 wheels?
Both use a 15" rim, so the wheel diameter matches; check the wheel's width range for a 267 mm tire and the fender clearance.