Tire size comparison
215/75R15 vs 31x10.50R15
31x10.50R15 is +11.9% taller than 215/75R15: 31.0 in vs 27.7 in (+3.30 in), and 2.0 in wider. With 31x10.50R15 on a vehicle set up for 215/75R15, the speedometer shows 60 mph at an actual 67.2 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 215/75R15) · 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
215/75R15 vs 31x10.50R15: full comparison
| 215/75R15 | 31x10.50R15 | Difference | |
|---|---|---|---|
| Overall diameter | 27.70 in | 31.00 in | +3.30 in (+11.9%) |
| Width | 8.46 in | 10.50 in | +2.04 in (+24.0%) |
| Sidewall height | 6.35 in | 8.00 in | +1.65 in |
| Circumference | 87.0 in | 97.4 in | +10.4 in |
| Revs per mile (nominal) | 728 | 651 | −78 |
| Wheel diameter | 15 in | 15 in | ±0 in |
| Diameter in mm | 704 | 787 | +84 mm |
Speedometer difference
Your speedometer is calibrated for 215/75R15. Fitted with 31x10.50R15, the actual speed is the reading × 31.00 ÷ 27.70.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 22.4 mph | +2.4 mph |
| 30 mph | 33.6 mph | +3.6 mph |
| 45 mph | 50.4 mph | +5.4 mph |
| 55 mph | 61.6 mph | +6.6 mph |
| 60 mph | 67.2 mph | +7.2 mph |
| 70 mph | 78.3 mph | +8.3 mph |
| 80 mph | 89.5 mph | +9.5 mph |
Real tires: published diameters
215/75R15: 27.6–27.8 in published by 4 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: 215/75R15 · 31x10.50R15
Related comparisons
FAQ
Which is bigger, 215/75R15 or 31x10.50R15?
31x10.50R15 is +11.9% taller than 215/75R15: 31.0 in vs 27.7 in (+3.30 in).
How much will my speedometer be off with 31x10.50R15 instead of 215/75R15?
The speedometer is calibrated for 215/75R15. With 31x10.50R15 it shows 60 mph when you are doing 67.2 mph, and 70 mph at 78.3 mph (+11.9%). Your speedometer also has its own factory tolerance.
Can I replace 215/75R15 with 31x10.50R15?
The diameter difference is +11.9%. 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.