255/35ZR21 vs 265/40R21
265/40R21 is taller than 255/35ZR21 by 4.71% — a diameter difference of 1.32″.
What changes between 255/35ZR21 and 265/40R21
Switching from 255/35ZR21 to 265/40R21 changes overall diameter by +4.71%, a taller tire by 1.32 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 +0.39″ (255mm → 265mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.66″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -33, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 68.1 mph. Both sizes share the same 21″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 255/35ZR21 | 265/40R21 |
|---|---|---|
| Overall diameter | 28.03″ | 29.35″ |
| Section width | 10.04″ (255 mm) | 10.43″ (265 mm) |
| Sidewall height | 3.51″ (35%) | 4.17″ (40%) |
| Rim diameter | 21″ | 21″ |
| Circumference | 88.05″ | 92.19″ |
| Revs per mile | 720 | 687 |
Interactive comparison
275/65R18 or "33" for inch aliases255/35ZR21
- Diameter
- 28.03″ / 711.9mm
- Section Width
- 10.04″
- Sidewall
- 3.51″ / 89.25mm
- Circumference
- 88.05″
- Revs/Mile
- 720
265/40R21
- Diameter
- 29.35″ / 745.4mm
- Section Width
- 10.43″
- Sidewall
- 4.17″ / 106mm
- Circumference
- 92.19″
- Revs/Mile
- 687
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 62.82 mph (101.1 km/h). Your speedometer reads 4.71% low versus actual speed.