Tire size comparison
33x12.50R15 vs 31x10.50R15
31x10.50R15 is −6.1% shorter than 33x12.50R15: 31.0 in vs 33.0 in (−2.00 in), and 2.0 in narrower. With 31x10.50R15 on a vehicle set up for 33x12.50R15, the speedometer shows 60 mph at an actual 56.4 mph. That is more than the ±3% difference many shops use as a rule of thumb, so check carefully before switching.
Set up for: going smaller (31x10.50R15 instead of 33x12.50R15) · Different situation?
Your current size
e.g. 265/70R17, 2657017 or 33x12.50R20
Where do I find my size?
It's on the tire sidewall, e.g. P265/70R17 115T, and on the tire placard sticker on the driver's door jamb (also in the owner's manual). The placard shows the size the vehicle came with; the sidewall shows what is fitted now. If they differ, use the placard as your starting point. Digits are enough here: 2657017 or 33125020.
Size you're considering
33x12.50R15 vs 31x10.50R15: full comparison
| 33x12.50R15 | 31x10.50R15 | Difference | |
|---|---|---|---|
| Overall diameter | 33.00 in | 31.00 in | −2.00 in (−6.1%) |
| Width | 12.50 in | 10.50 in | −2.00 in (−16.0%) |
| Sidewall height | 9.00 in | 8.00 in | −1.00 in |
| Circumference | 103.7 in | 97.4 in | −6.3 in |
| Revs per mile (nominal) | 611 | 651 | +39 |
| Wheel diameter | 15 in | 15 in | ±0 in |
| Diameter in mm | 838 | 787 | −51 mm |
Speedometer difference
Your speedometer is calibrated for 33x12.50R15. Fitted with 31x10.50R15, the actual speed is the reading × 31.00 ÷ 33.00.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 18.8 mph | −1.2 mph |
| 30 mph | 28.2 mph | −1.8 mph |
| 45 mph | 42.3 mph | −2.7 mph |
| 55 mph | 51.7 mph | −3.3 mph |
| 60 mph | 56.4 mph | −3.6 mph |
| 70 mph | 65.8 mph | −4.2 mph |
| 80 mph | 75.2 mph | −4.8 mph |
Real tires: published diameters
33x12.50R15: 32.5–33.1 in published by 5 makers; 31x10.50R15: 30.5–31.1 in published by 4 makers. Calculated figures assume a nominal tire; the exact difference between two specific tires depends on their models.
More about each size: 33x12.50R15 · 31x10.50R15
Related comparisons
FAQ
Which is bigger, 33x12.50R15 or 31x10.50R15?
31x10.50R15 is −6.1% shorter than 33x12.50R15: 31.0 in vs 33.0 in (−2.00 in).
How much will my speedometer be off with 31x10.50R15 instead of 33x12.50R15?
The speedometer is calibrated for 33x12.50R15. With 31x10.50R15 it shows 60 mph when you are doing 56.4 mph, and 70 mph at 65.8 mph (−6.1%). Your speedometer also has its own factory tolerance.
Can I replace 33x12.50R15 with 31x10.50R15?
The diameter difference is −6.1%. Whether it fits depends on things this calculation can't see: wheel width and offset, clearance at full lock and over bumps, load index and speed rating, and your vehicle maker's approval. Check your door-jamb placard and owner's manual and ask a tire professional.