Tire size comparison
245/35R20 vs 255/35R20
255/35R20 is +1.0% taller than 245/35R20: 27.0 in vs 26.8 in (+0.28 in), and 0.4 in wider. With 255/35R20 on a vehicle set up for 245/35R20, the speedometer shows 60 mph at an actual 60.6 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 (255/35R20 instead of 245/35R20) · 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
245/35R20 vs 255/35R20: full comparison
| 245/35R20 | 255/35R20 | Difference | |
|---|---|---|---|
| Overall diameter | 26.75 in | 27.03 in | +0.28 in (+1.0%) |
| Width | 9.65 in | 10.04 in | +0.39 in (+4.1%) |
| Sidewall height | 3.38 in | 3.51 in | +0.14 in |
| Circumference | 84.0 in | 84.9 in | +0.9 in |
| Revs per mile (nominal) | 754 | 746 | −8 |
| Wheel diameter | 20 in | 20 in | ±0 in |
| Diameter in mm | 680 | 686 | +7 mm |
Speedometer difference
Your speedometer is calibrated for 245/35R20. Fitted with 255/35R20, the actual speed is the reading × 27.03 ÷ 26.75.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 20.2 mph | +0.2 mph |
| 30 mph | 30.3 mph | +0.3 mph |
| 45 mph | 45.5 mph | +0.5 mph |
| 55 mph | 55.6 mph | +0.6 mph |
| 60 mph | 60.6 mph | +0.6 mph |
| 70 mph | 70.7 mph | +0.7 mph |
| 80 mph | 80.8 mph | +0.8 mph |
Real tires: published diameters
245/35R20: 26.6–26.9 in published by 7 makers; 255/35R20: 26.5–27.2 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: 245/35R20 · 255/35R20
FAQ
Which is bigger, 245/35R20 or 255/35R20?
255/35R20 is +1.0% taller than 245/35R20: 27.0 in vs 26.8 in (+0.28 in).
How much will my speedometer be off with 255/35R20 instead of 245/35R20?
The speedometer is calibrated for 245/35R20. With 255/35R20 it shows 60 mph when you are doing 60.6 mph, and 70 mph at 70.7 mph (+1.0%). Your speedometer also has its own factory tolerance.
Can I replace 245/35R20 with 255/35R20?
The diameter difference is +1.0%. 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.