255/45R20 vs 275/45R20
275/45R20 is taller than 255/45R20 by 2.44% — a diameter difference of 0.70″.
What changes between 255/45R20 and 275/45R20
Switching from 255/45R20 to 275/45R20 changes overall diameter by +2.44%, a taller tire by 0.70 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 +0.79″ (255mm → 275mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.35″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -17, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 66.6 mph. Both sizes share the same 20″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 255/45R20 | 275/45R20 |
|---|---|---|
| Overall diameter | 29.04″ | 29.74″ |
| Section width | 10.04″ (255 mm) | 10.83″ (275 mm) |
| Sidewall height | 4.52″ (45%) | 4.87″ (45%) |
| Rim diameter | 20″ | 20″ |
| Circumference | 91.22″ | 93.44″ |
| Revs per mile | 695 | 678 |
Interactive comparison
275/65R18 or "33" for inch aliases255/45R20
- Diameter
- 29.04″ / 737.5mm
- Section Width
- 10.04″
- Sidewall
- 4.52″ / 114.75mm
- Circumference
- 91.22″
- Revs/Mile
- 695
275/45R20
- Diameter
- 29.74″ / 755.5mm
- Section Width
- 10.83″
- Sidewall
- 4.87″ / 123.75mm
- Circumference
- 93.44″
- Revs/Mile
- 678
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 61.46 mph (98.92 km/h). Your speedometer reads 2.44% low versus actual speed.