255/35R20 vs 255/40R20
255/40R20 is taller than 255/35R20 by 3.71% — a diameter difference of 1.00″.
What changes between 255/35R20 and 255/40R20
Switching from 255/35R20 to 255/40R20 changes overall diameter by +3.71%, a taller tire by 1.00 inches. This sits in the 3–5% caution band, where rubbing at full steering lock or suspension compression becomes possible. Leveling kits or fender-liner trims are often needed on lifted trucks. Section width moves by 0.00″ (255mm → 255mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.51″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -27, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 67.4 mph. Both sizes share the same 20″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 255/35R20 | 255/40R20 |
|---|---|---|
| Overall diameter | 27.03″ | 28.03″ |
| Section width | 10.04″ (255 mm) | 10.04″ (255 mm) |
| Sidewall height | 3.51″ (35%) | 4.02″ (40%) |
| Rim diameter | 20″ | 20″ |
| Circumference | 84.91″ | 88.06″ |
| Revs per mile | 746 | 719 |
Interactive comparison
275/65R18 or "33" for inch aliases255/35R20
- Diameter
- 27.03″ / 686.5mm
- Section Width
- 10.04″
- Sidewall
- 3.51″ / 89.25mm
- Circumference
- 84.91″
- Revs/Mile
- 746
255/40R20
- Diameter
- 28.03″ / 712mm
- Section Width
- 10.04″
- Sidewall
- 4.02″ / 102mm
- Circumference
- 88.06″
- Revs/Mile
- 719
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 62.23 mph (100.15 km/h). Your speedometer reads 3.71% low versus actual speed.