Tire size comparison
285/70R17 vs 315/70R17
315/70R17 is +5.1% taller than 285/70R17: 34.4 in vs 32.7 in (+1.65 in), and 1.2 in wider. With 315/70R17 on a vehicle set up for 285/70R17, the speedometer shows 60 mph at an actual 63.0 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 (315/70R17 instead of 285/70R17) · 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
285/70R17 vs 315/70R17: full comparison
| 285/70R17 | 315/70R17 | Difference | |
|---|---|---|---|
| Overall diameter | 32.71 in | 34.36 in | +1.65 in (+5.1%) |
| Width | 11.22 in | 12.40 in | +1.18 in (+10.5%) |
| Sidewall height | 7.85 in | 8.68 in | +0.83 in |
| Circumference | 102.8 in | 108.0 in | +5.2 in |
| Revs per mile (nominal) | 617 | 587 | −30 |
| Wheel diameter | 17 in | 17 in | ±0 in |
| Diameter in mm | 831 | 873 | +42 mm |
Speedometer difference
Your speedometer is calibrated for 285/70R17. Fitted with 315/70R17, the actual speed is the reading × 34.36 ÷ 32.71.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 21.0 mph | +1.0 mph |
| 30 mph | 31.5 mph | +1.5 mph |
| 45 mph | 47.3 mph | +2.3 mph |
| 55 mph | 57.8 mph | +2.8 mph |
| 60 mph | 63.0 mph | +3.0 mph |
| 70 mph | 73.5 mph | +3.5 mph |
| 80 mph | 84.0 mph | +4.0 mph |
Real tires: published diameters
285/70R17: 32.7–33.15 in published by 6 makers; 315/70R17: 34.4–34.7 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: 285/70R17 · 315/70R17
Related comparisons
FAQ
Which is bigger, 285/70R17 or 315/70R17?
315/70R17 is +5.1% taller than 285/70R17: 34.4 in vs 32.7 in (+1.65 in).
How much will my speedometer be off with 315/70R17 instead of 285/70R17?
The speedometer is calibrated for 285/70R17. With 315/70R17 it shows 60 mph when you are doing 63.0 mph, and 70 mph at 73.5 mph (+5.1%). Your speedometer also has its own factory tolerance.
Can I replace 285/70R17 with 315/70R17?
The diameter difference is +5.1%. 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.