Tire size comparison
265/75R15 vs 31x10.50R15
31x10.50R15 is +1.1% taller than 265/75R15: 31.0 in vs 30.6 in (+0.35 in), and 0.1 in wider. With 31x10.50R15 on a vehicle set up for 265/75R15, the speedometer shows 60 mph at an actual 60.7 mph. That is within the ±3% difference many shops use as a rule of thumb (not a manufacturer or legal limit).
Set up for: checking a replacement size (31x10.50R15 instead of 265/75R15) · 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
265/75R15 vs 31x10.50R15: full comparison
| 265/75R15 | 31x10.50R15 | Difference | |
|---|---|---|---|
| Overall diameter | 30.65 in | 31.00 in | +0.35 in (+1.1%) |
| Width | 10.43 in | 10.50 in | +0.07 in (+0.6%) |
| Sidewall height | 7.82 in | 8.00 in | +0.18 in |
| Circumference | 96.3 in | 97.4 in | +1.1 in |
| Revs per mile (nominal) | 658 | 651 | −7 |
| Wheel diameter | 15 in | 15 in | ±0 in |
| Diameter in mm | 778 | 787 | +9 mm |
Speedometer difference
Your speedometer is calibrated for 265/75R15. Fitted with 31x10.50R15, the actual speed is the reading × 31.00 ÷ 30.65.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 20.2 mph | +0.2 mph |
| 30 mph | 30.3 mph | +0.3 mph |
| 45 mph | 45.5 mph | +0.5 mph |
| 55 mph | 55.6 mph | +0.6 mph |
| 60 mph | 60.7 mph | +0.7 mph |
| 70 mph | 70.8 mph | +0.8 mph |
| 80 mph | 80.9 mph | +0.9 mph |
Real tires: published diameters
265/75R15: 30.7 in published by 1 maker; 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: 265/75R15 · 31x10.50R15
Related comparisons
FAQ
Which is bigger, 265/75R15 or 31x10.50R15?
31x10.50R15 is +1.1% taller than 265/75R15: 31.0 in vs 30.6 in (+0.35 in).
How much will my speedometer be off with 31x10.50R15 instead of 265/75R15?
The speedometer is calibrated for 265/75R15. With 31x10.50R15 it shows 60 mph when you are doing 60.7 mph, and 70 mph at 70.8 mph (+1.1%). Your speedometer also has its own factory tolerance.
Can I replace 265/75R15 with 31x10.50R15?
The diameter difference is +1.1%. 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.