255/45R21 tire size
A 255/45R21 tire is 30.04 inches (762.9 mm) tall, 10.04 in (255 mm) wide and fits a 21-inch wheel. In inch notation it is roughly a 30.0x10.0R21 — a "30-inch" tire.
| Overall diameter | 30.04 in | 762.9 mm |
|---|---|---|
| Section width | 10.04 in | 255 mm |
| Sidewall height | 4.52 in | 114.8 mm |
| Circumference | 94.36 in | 2,397 mm |
| Revolutions | 671.5 per mile | 417.2 per km |
| Rim diameter | 21 in | 533.4 mm |
Compare 255/45R21 with another size
Alternative sizes on the same 21-inch wheel
Sizes in use within ±3 % of the overall diameter of 255/45R21:
Plus and minus sizes for 255/45R21
| Size | Wheel | Diameter | Difference |
|---|---|---|---|
| 255/55R19 | Minus 2 (19 in) | 30.04 in | +0.03% |
| 235/60R19 | Minus 2 (19 in) | 30.10 in | +0.22% |
| 275/50R19 | Minus 2 (19 in) | 29.83 in | −0.69% |
| 265/55R19 | Minus 2 (19 in) | 30.48 in | +1.47% |
| 255/50R20 | Minus 1 (20 in) | 30.04 in | +0.01% |
| 285/45R20 | Minus 1 (20 in) | 30.10 in | +0.21% |
| 235/55R20 | Minus 1 (20 in) | 30.18 in | +0.47% |
| 275/45R20 | Minus 1 (20 in) | 29.74 in | −0.97% |
| 255/40R22 | Plus 1 (22 in) | 30.03 in | −0.01% |
| 295/35R22 | Plus 1 (22 in) | 30.13 in | +0.31% |
| 285/35R22 | Plus 1 (22 in) | 29.85 in | −0.60% |
| 265/40R22 | Plus 1 (22 in) | 30.35 in | +1.04% |
| 275/35R23 | Plus 2 (23 in) | 30.58 in | +1.81% |
| 285/35R23 | Plus 2 (23 in) | 30.85 in | +2.73% |
Vehicles approved with 255/45R21 tires
Models whose Swiss type approval lists 255/45R21 as a standard or optional size (23 approvals in total). Always check your own vehicle's placard or papers.
Source: Swiss Federal Roads Office (FEDRO/ASTRA), open government data. Original data (downloaded 2026-09-29). Data processed by us; errors in processing are ours, not the publisher's.
Nearby 21-inch sizes
Reading the 255/45R21 size
- 255 — section width in millimetres (10.04 in).
- 45 — aspect ratio: the sidewall is 45 % of the width, 114.8 mm.
- R — radial construction (ZR on the sidewall means a high-speed rated radial; the dimensions are the same).
- 21 — fits a 21-inch diameter wheel.
The load index and speed rating (for example 91V) follow the size on the sidewall. They must meet at least the values on your vehicle's tire placard.