305/40R21 tire size
A 305/40R21 tire is 30.61 inches (777.4 mm) tall, 12.01 in (305 mm) wide and fits a 21-inch wheel. In inch notation it is roughly a 30.6x12.0R21 — a "31-inch" tire.
| Overall diameter | 30.61 in | 777.4 mm |
|---|---|---|
| Section width | 12.01 in | 305 mm |
| Sidewall height | 4.80 in | 122.0 mm |
| Circumference | 96.15 in | 2,442 mm |
| Revolutions | 659.0 per mile | 409.5 per km |
| Rim diameter | 21 in | 533.4 mm |
Compare 305/40R21 with another size
Alternative sizes on the same 21-inch wheel
Sizes in use within ±3 % of the overall diameter of 305/40R21:
Plus and minus sizes for 305/40R21
| Size | Wheel | Diameter | Difference |
|---|---|---|---|
| 275/55R19 | Minus 2 (19 in) | 30.91 in | +0.99% |
| 275/50R19 | Minus 2 (19 in) | 29.83 in | −2.55% |
| 295/45R20 | Minus 1 (20 in) | 30.45 in | −0.50% |
| 275/50R20 | Minus 1 (20 in) | 30.83 in | +0.72% |
| 285/45R20 | Minus 1 (20 in) | 30.10 in | −1.66% |
| 285/50R20 | Minus 1 (20 in) | 31.22 in | +2.01% |
| 275/40R22 | Plus 1 (22 in) | 30.66 in | +0.18% |
| 315/35R22 | Plus 1 (22 in) | 30.68 in | +0.24% |
| 325/35R22 | Plus 1 (22 in) | 30.96 in | +1.14% |
| 285/40R22 | Plus 1 (22 in) | 30.98 in | +1.21% |
| 275/35R23 | Plus 2 (23 in) | 30.58 in | −0.09% |
| 325/30R23 | Plus 2 (23 in) | 30.68 in | +0.23% |
| 315/30R23 | Plus 2 (23 in) | 30.44 in | −0.54% |
| 285/35R23 | Plus 2 (23 in) | 30.85 in | +0.81% |
Nearby 21-inch sizes
Reading the 305/40R21 size
- 305 — section width in millimetres (12.01 in).
- 40 — aspect ratio: the sidewall is 40 % of the width, 122.0 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.