ElpiAuto31X10.50R15 vs 33X12.50R15
33X12.50R15 is 6.5% taller (51 mm) than 31X10.50R15 — outside the ±3% swap band.
Two sizes
Also accepts 35X12.50R17 and 31x10.5-15.
Both sizes, drawn to scale
1 grid = 1 inWhat each number means
The two size codes broken down — which digit is which, and what it does on the car.
Size A — 31X10.50R15
- 31overall height31.0″ tall — stated directly, no math
- 10.5section width10.5″ across the tread
- R15wheel diametermounts on a 15-inch wheel
In metric sizing: ≈ 265/75R15
Size B — 33X12.50R15
- 33overall height33.0″ tall — stated directly, no math
- 12.5section width12.5″ across the tread
- R15wheel diametermounts on a 15-inch wheel
In metric sizing: ≈ 320/70R15
31X10.50R15 vs 33X12.50R15, measurement by measurement
Every dimension in inches, with the difference and which size is bigger
| Measurement | 31X10.50R15 | 33X12.50R15 | Difference | % |
|---|---|---|---|---|
| Overall diameter | 31.00″ | 33.00″ | +2.00″ | +6.5% |
| Section width | 10.50″ | 12.50″ | +2.00″ | +19.0% |
| Sidewall height | 8.00″ | 9.00″ | +1.00″ | +12.5% |
| Circumference | 97.39″ | 103.67″ | +6.28″ | +6.5% |
| Revs per mile | 650.6 | 611.2 | −39.4 | −6.1% |
| Revs per km | 404.3 | 379.8 | −24.5 | −6.1% |
| Approved rim width estimate | 7.5–10″ | 9.5–12″ | — | — |
Overall diameter is the controlling number — clearance, gearing, speedometer accuracy and odometer reading all follow from it. Revs per mile/km is what your ABS, speedometer and odometer actually count.
What changes on the road
Direction and rough size of each effect going from 31X10.50R15 to 33X12.50R15. Geometry only — real tires vary by brand and compound.
Speedometer & odometer error
What changes on the dash when the overall diameter changes.
A speedometer doesn't measure distance. It counts how fast the wheels turn and multiplies by a fixed factory number for tire circumference. Change the tire and that factory number is now wrong.
Going to a bigger tire, each turn covers more ground, so at a true 63.9 mph the wheels spin at the rate the factory calls 60. The dial reads low — you are speeding without knowing it. A smaller tire does the opposite, and the odometer also over-counts miles you didn't drive.
Over 10,000 indicated miles, this change means the odometer under-counts by roughly 606 miles.
| Speedometer reads | True speed on 33X12.50R15 | Error |
|---|---|---|
| 20 mph | 21.3 mph | +1.3 |
| 30 mph | 31.9 mph | +1.9 |
| 40 mph | 42.6 mph | +2.6 |
| 50 mph | 53.2 mph | +3.2 |
| 60 mph | 63.9 mph | +3.9 |
| 70 mph | 74.5 mph | +4.5 |
| 80 mph | 85.2 mph | +5.2 |
With 31X10.50R15 as the original size. A taller tire makes the dial read low — the gap grows with speed.
Reading this comparison
The overall diameter is what matters here: 33X12.50R15 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.