275/45R21 vs 285/45R21
285/45R21 is taller than 275/45R21 by 1.15% — a diameter difference of 0.36″.
What changes between 275/45R21 and 285/45R21
Switching from 275/45R21 to 285/45R21 changes overall diameter by +1.15%, a taller tire by 0.36 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 +0.18″: 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 65.8 mph. Both sizes share the same 21″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 275/45R21 | 285/45R21 |
|---|---|---|
| Overall diameter | 30.74″ | 31.1″ |
| Section width | 10.83″ (275 mm) | 11.22″ (285 mm) |
| Sidewall height | 4.87″ (45%) | 5.05″ (45%) |
| Rim diameter | 21″ | 21″ |
| Circumference | 96.59″ | 97.7″ |
| Revs per mile | 656 | 649 |
Interactive comparison
275/65R18 or "33" for inch aliases275/45R21
- Diameter
- 30.74″ / 780.9mm
- Section Width
- 10.83″
- Sidewall
- 4.87″ / 123.75mm
- Circumference
- 96.59″
- Revs/Mile
- 656
285/45R21
- Diameter
- 31.1″ / 789.9mm
- Section Width
- 11.22″
- Sidewall
- 5.05″ / 128.25mm
- Circumference
- 97.7″
- Revs/Mile
- 649
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 60.69 mph (97.67 km/h). Your speedometer reads 1.15% low versus actual speed.