Tire size comparison
315/70R17 vs 37x12.50R17
37x12.50R17 is +7.7% taller than 315/70R17: 37.0 in vs 34.4 in (+2.64 in), and 0.1 in wider. With 37x12.50R17 on a vehicle set up for 315/70R17, the speedometer shows 60 mph at an actual 64.6 mph. That is more than the ±3% difference many shops use as a rule of thumb, so check carefully before switching.
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). If your current tires aren't the original size, the placard shows what the vehicle came with. Digits are enough here: 2657017 or 33125020.
Size you're considering
315/70R17 vs 37x12.50R17: full comparison
| 315/70R17 | 37x12.50R17 | Difference | |
|---|---|---|---|
| Overall diameter | 34.36 in | 37.00 in | +2.64 in (+7.7%) |
| Width | 12.40 in | 12.50 in | +0.10 in (+0.8%) |
| Sidewall height | 8.68 in | 10.00 in | +1.32 in |
| Circumference | 108.0 in | 116.2 in | +8.3 in |
| Revs per mile (nominal) | 587 | 545 | −42 |
| Wheel diameter | 17 in | 17 in | ±0 in |
| Diameter in mm | 873 | 940 | +67 mm |
Speedometer difference
Your speedometer is calibrated for 315/70R17. Fitted with 37x12.50R17, the actual speed is the reading × 37.00 ÷ 34.36.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 21.5 mph | +1.5 mph |
| 30 mph | 32.3 mph | +2.3 mph |
| 45 mph | 48.5 mph | +3.5 mph |
| 55 mph | 59.2 mph | +4.2 mph |
| 60 mph | 64.6 mph | +4.6 mph |
| 70 mph | 75.4 mph | +5.4 mph |
| 80 mph | 86.1 mph | +6.1 mph |
Real tires: published diameters
315/70R17: 34.4–34.7 in published by 5 makers; 37x12.50R17: 36.54–37 in published by 5 makers. Calculated figures assume a nominal tire; the exact difference between two specific tires depends on their models.
More about each size: 315/70R17 · 37x12.50R17
Related comparisons
FAQ
Which is bigger, 315/70R17 or 37x12.50R17?
37x12.50R17 is +7.7% taller than 315/70R17: 37.0 in vs 34.4 in (+2.64 in).
How much will my speedometer be off with 37x12.50R17 instead of 315/70R17?
The speedometer is calibrated for 315/70R17. With 37x12.50R17 it shows 60 mph when you are doing 64.6 mph, and 70 mph at 75.4 mph (+7.7%). Your speedometer also has its own factory tolerance.
Can I replace 315/70R17 with 37x12.50R17?
The diameter difference is +7.7%. 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.