245/35ZR20 vs 255/35R20
255/35R20 is taller than 245/35ZR20 by 1.03% — a diameter difference of 0.28″.
What changes between 245/35ZR20 and 255/35R20
Switching from 245/35ZR20 to 255/35R20 changes overall diameter by +1.03%, a taller tire by 0.28 inches. This lands inside the ±3% fitment safe zone, so most vehicles will accept the swap without rubbing, speedometer recalibration, or ABS/TPMS complications. Section width moves by +0.39″ (245mm → 255mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.13″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -8, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 65.7 mph. Both sizes share the same 20″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 245/35ZR20 | 255/35R20 |
|---|---|---|
| Overall diameter | 26.75″ | 27.03″ |
| Section width | 9.65″ (245 mm) | 10.04″ (255 mm) |
| Sidewall height | 3.38″ (35%) | 3.51″ (35%) |
| Rim diameter | 20″ | 20″ |
| Circumference | 84.04″ | 84.91″ |
| Revs per mile | 754 | 746 |
Interactive comparison
275/65R18 or "33" for inch aliases245/35ZR20
- Diameter
- 26.75″ / 679.5mm
- Section Width
- 9.65″
- Sidewall
- 3.38″ / 85.75mm
- Circumference
- 84.04″
- Revs/Mile
- 754
255/35R20
- Diameter
- 27.03″ / 686.5mm
- Section Width
- 10.04″
- Sidewall
- 3.51″ / 89.25mm
- Circumference
- 84.91″
- Revs/Mile
- 746
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 60.62 mph (97.56 km/h). Your speedometer reads 1.03% low versus actual speed.