Tire size comparison
255/40R18 vs 265/35R18
265/35R18 is −2.8% shorter than 255/40R18: 25.3 in vs 26.0 in (−0.73 in), and 0.4 in wider. With 265/35R18 on a vehicle set up for 255/40R18, the speedometer shows 60 mph at an actual 58.3 mph. That is within the ±3% difference many shops use as a rule of thumb (not a manufacturer or legal limit).
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
255/40R18 vs 265/35R18: full comparison
| 255/40R18 | 265/35R18 | Difference | |
|---|---|---|---|
| Overall diameter | 26.03 in | 25.30 in | −0.73 in (−2.8%) |
| Width | 10.04 in | 10.43 in | +0.39 in (+3.9%) |
| Sidewall height | 4.02 in | 3.65 in | −0.36 in |
| Circumference | 81.8 in | 79.5 in | −2.3 in |
| Revs per mile (nominal) | 775 | 797 | +22 |
| Wheel diameter | 18 in | 18 in | ±0 in |
| Diameter in mm | 661 | 643 | −18 mm |
Speedometer difference
Your speedometer is calibrated for 255/40R18. Fitted with 265/35R18, the actual speed is the reading × 25.30 ÷ 26.03.
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 19.4 mph | −0.6 mph |
| 30 mph | 29.2 mph | −0.8 mph |
| 45 mph | 43.7 mph | −1.3 mph |
| 55 mph | 53.5 mph | −1.5 mph |
| 60 mph | 58.3 mph | −1.7 mph |
| 70 mph | 68.0 mph | −2.0 mph |
| 80 mph | 77.8 mph | −2.2 mph |
Real tires: published diameters
255/40R18: 25.8–26.2 in published by 5 makers; 265/35R18: 25.1–25.4 in published by 7 makers. Calculated figures assume a nominal tire; the exact difference between two specific tires depends on their models.
More about each size: 255/40R18 · 265/35R18
FAQ
Which is bigger, 255/40R18 or 265/35R18?
265/35R18 is −2.8% shorter than 255/40R18: 25.3 in vs 26.0 in (−0.73 in).
How much will my speedometer be off with 265/35R18 instead of 255/40R18?
The speedometer is calibrated for 255/40R18. With 265/35R18 it shows 60 mph when you are doing 58.3 mph, and 70 mph at 68.0 mph (−2.8%). Your speedometer also has its own factory tolerance.
Can I replace 255/40R18 with 265/35R18?
The diameter difference is −2.8%. 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.