305/40R20 tire size
A 305/40R20 tire is 29.61 inches (752.0 mm) tall, 12.01 in (305 mm) wide and fits a 20-inch wheel. In inch notation it is roughly a 29.6x12.0R20 — a "30-inch" tire.
| Overall diameter | 29.61 in | 752.0 mm |
|---|---|---|
| Section width | 12.01 in | 305 mm |
| Sidewall height | 4.80 in | 122.0 mm |
| Circumference | 93.01 in | 2,362 mm |
| Revolutions | 681.2 per mile | 423.3 per km |
| Rim diameter | 20 in | 508.0 mm |
Compare 305/40R20 with another size
Alternative sizes on the same 20-inch wheel
Sizes in use within ±3 % of the overall diameter of 305/40R20:
Plus and minus sizes for 305/40R20
| Size | Wheel | Diameter | Difference |
|---|---|---|---|
| 285/50R18 | Minus 2 (18 in) | 29.22 in | −1.30% |
| 285/55R18 | Minus 2 (18 in) | 30.34 in | +2.49% |
| 295/45R19 | Minus 1 (19 in) | 29.45 in | −0.52% |
| 275/50R19 | Minus 1 (19 in) | 29.83 in | +0.74% |
| 285/45R19 | Minus 1 (19 in) | 29.10 in | −1.72% |
| 275/45R19 | Minus 1 (19 in) | 28.74 in | −2.91% |
| 275/40R21 | Plus 1 (21 in) | 29.66 in | +0.19% |
| 315/35R21 | Plus 1 (21 in) | 29.68 in | +0.25% |
| 305/35R21 | Plus 1 (21 in) | 29.41 in | −0.68% |
| 285/40R21 | Plus 1 (21 in) | 29.98 in | +1.25% |
| 275/35R22 | Plus 2 (22 in) | 29.58 in | −0.09% |
| 315/30R22 | Plus 2 (22 in) | 29.44 in | −0.56% |
| 285/35R22 | Plus 2 (22 in) | 29.85 in | +0.84% |
| 305/30R22 | Plus 2 (22 in) | 29.20 in | −1.36% |
| 315/30R23 | Plus 3 (23 in) | 30.44 in | +2.82% |
Vehicles approved with 305/40R20 tires
Models whose Swiss type approval lists 305/40R20 as a standard or optional size (1,902 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 20-inch sizes
Reading the 305/40R20 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).
- 20 — fits a 20-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.