325/40R21 tire size
A 325/40R21 tire is 31.24 inches (793.4 mm) tall, 12.80 in (325 mm) wide and fits a 21-inch wheel. In inch notation it is roughly a 31.2x12.8R21 — a "31-inch" tire.
| Overall diameter | 31.24 in | 793.4 mm |
|---|---|---|
| Section width | 12.80 in | 325 mm |
| Sidewall height | 5.12 in | 130.0 mm |
| Circumference | 98.13 in | 2,493 mm |
| Revolutions | 645.7 per mile | 401.2 per km |
| Rim diameter | 21 in | 533.4 mm |
Compare 325/40R21 with another size
Alternative sizes on the same 21-inch wheel
Sizes in use within ±3 % of the overall diameter of 325/40R21:
Plus and minus sizes for 325/40R21
| Size | Wheel | Diameter | Difference |
|---|---|---|---|
| 295/45R20 | Minus 1 (20 in) | 30.45 in | −2.51% |
| 295/40R22 | Plus 1 (22 in) | 31.29 in | +0.18% |
| 325/35R22 | Plus 1 (22 in) | 30.96 in | −0.89% |
| 305/40R22 | Plus 1 (22 in) | 31.61 in | +1.18% |
| 315/35R22 | Plus 1 (22 in) | 30.68 in | −1.78% |
| 295/35R23 | Plus 2 (23 in) | 31.13 in | −0.34% |
| 305/35R23 | Plus 2 (23 in) | 31.41 in | +0.54% |
| 325/30R23 | Plus 2 (23 in) | 30.68 in | −1.79% |
| 325/35R23 | Plus 2 (23 in) | 31.96 in | +2.31% |
Vehicles approved with 325/40R21 tires
Models whose Swiss type approval lists 325/40R21 as a standard or optional size (12 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 325/40R21 size
- 325 — section width in millimetres (12.80 in).
- 40 — aspect ratio: the sidewall is 40 % of the width, 130.0 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.