Tire size comparison
255/80R17 vs 285/70R17
285/70R17 is −1.1% shorter than 255/80R17: 32.7 in vs 33.1 in (−0.35 in), and 1.2 in wider. With 285/70R17 on a vehicle set up for 255/80R17, the speedometer shows 60 mph at an actual 59.4 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 (285/70R17 instead of 255/80R17) · 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
255/80R17 vs 285/70R17: full comparison
| 255/80R17 | 285/70R17 | Difference | |
|---|---|---|---|
| Overall diameter | 33.06 in | 32.71 in | −0.35 in (−1.1%) |
| Width | 10.04 in | 11.22 in | +1.18 in (+11.8%) |
| Sidewall height | 8.03 in | 7.85 in | −0.18 in |
| Circumference | 103.9 in | 102.8 in | −1.1 in |
| Revs per mile (nominal) | 610 | 617 | +7 |
| Wheel diameter | 17 in | 17 in | ±0 in |
| Diameter in mm | 840 | 831 | −9 mm |
Speedometer difference
Your speedometer is calibrated for 255/80R17. Fitted with 285/70R17, the actual speed is the reading × 32.71 ÷ 33.06.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 19.8 mph | −0.2 mph |
| 30 mph | 29.7 mph | −0.3 mph |
| 45 mph | 44.5 mph | −0.5 mph |
| 55 mph | 54.4 mph | −0.6 mph |
| 60 mph | 59.4 mph | −0.6 mph |
| 70 mph | 69.2 mph | −0.8 mph |
| 80 mph | 79.1 mph | −0.9 mph |
Real tires: published diameters
255/80R17: 33–33.31 in published by 5 makers; 285/70R17: 32.7–33.15 in published by 6 makers. Calculated figures assume a nominal tire; the exact difference between two specific tires depends on their models.
More about each size: 255/80R17 · 285/70R17
Related comparisons
FAQ
Which is bigger, 255/80R17 or 285/70R17?
285/70R17 is −1.1% shorter than 255/80R17: 32.7 in vs 33.1 in (−0.35 in).
How much will my speedometer be off with 285/70R17 instead of 255/80R17?
The speedometer is calibrated for 255/80R17. With 285/70R17 it shows 60 mph when you are doing 59.4 mph, and 70 mph at 69.2 mph (−1.1%). Your speedometer also has its own factory tolerance.
Can I replace 255/80R17 with 285/70R17?
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.