275/30ZR20 vs 285/30R20
285/30R20 is taller than 275/30ZR20 by 0.89% — a diameter difference of 0.23″.
What changes between 275/30ZR20 and 285/30R20
Switching from 275/30ZR20 to 285/30R20 changes overall diameter by +0.89%, a taller tire by 0.23 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″ (275mm → 285mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.12″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -7, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 65.6 mph. Both sizes share the same 20″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 275/30ZR20 | 285/30R20 |
|---|---|---|
| Overall diameter | 26.5″ | 26.73″ |
| Section width | 10.83″ (275 mm) | 11.22″ (285 mm) |
| Sidewall height | 3.25″ (30%) | 3.37″ (30%) |
| Rim diameter | 20″ | 20″ |
| Circumference | 83.24″ | 83.98″ |
| Revs per mile | 761 | 754 |
Interactive comparison
275/65R18 or "33" for inch aliases275/30ZR20
- Diameter
- 26.5″ / 673mm
- Section Width
- 10.83″
- Sidewall
- 3.25″ / 82.5mm
- Circumference
- 83.24″
- Revs/Mile
- 761
285/30R20
- Diameter
- 26.73″ / 679mm
- Section Width
- 11.22″
- Sidewall
- 3.37″ / 85.5mm
- Circumference
- 83.98″
- Revs/Mile
- 754
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 60.53 mph (97.42 km/h). Your speedometer reads 0.89% low versus actual speed.