Tire size comparison
235/75R15 vs 31x10.50R15
31x10.50R15 is +7.3% taller than 235/75R15: 31.0 in vs 28.9 in (+2.12 in), and 1.2 in wider. With 31x10.50R15 on a vehicle set up for 235/75R15, the speedometer shows 60 mph at an actual 64.4 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 bigger (31x10.50R15 instead of 235/75R15) · 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
235/75R15 vs 31x10.50R15: full comparison
| 235/75R15 | 31x10.50R15 | Difference | |
|---|---|---|---|
| Overall diameter | 28.88 in | 31.00 in | +2.12 in (+7.3%) |
| Width | 9.25 in | 10.50 in | +1.25 in (+13.5%) |
| Sidewall height | 6.94 in | 8.00 in | +1.06 in |
| Circumference | 90.7 in | 97.4 in | +6.7 in |
| Revs per mile (nominal) | 698 | 651 | −48 |
| Wheel diameter | 15 in | 15 in | ±0 in |
| Diameter in mm | 733 | 787 | +54 mm |
Speedometer difference
Your speedometer is calibrated for 235/75R15. Fitted with 31x10.50R15, the actual speed is the reading × 31.00 ÷ 28.88.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 21.5 mph | +1.5 mph |
| 30 mph | 32.2 mph | +2.2 mph |
| 45 mph | 48.3 mph | +3.3 mph |
| 55 mph | 59.0 mph | +4.0 mph |
| 60 mph | 64.4 mph | +4.4 mph |
| 70 mph | 75.1 mph | +5.1 mph |
| 80 mph | 85.9 mph | +5.9 mph |
Real tires: published diameters
235/75R15: 28.7–29.1 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: 235/75R15 · 31x10.50R15
Related comparisons
FAQ
Which is bigger, 235/75R15 or 31x10.50R15?
31x10.50R15 is +7.3% taller than 235/75R15: 31.0 in vs 28.9 in (+2.12 in).
How much will my speedometer be off with 31x10.50R15 instead of 235/75R15?
The speedometer is calibrated for 235/75R15. With 31x10.50R15 it shows 60 mph when you are doing 64.4 mph, and 70 mph at 75.1 mph (+7.3%). Your speedometer also has its own factory tolerance.
Can I replace 235/75R15 with 31x10.50R15?
The diameter difference is +7.3%. 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.