179Best 325/40 R21 tires
1 rated tire available in this size, scored on dry, wet, snow, comfort and wear. Top overall right now is the Continental ContiSportContact 5P at 79/100.
31.2″
overall diameter
12.8″
section width
21″
rim diameter
645.7
revs per mile
Best 325/40 R21 summer tires
1179Conversion
325/40 R21 in inches
| Overall diameter | 31.2″ |
| Section width | 12.8″ |
| Rim diameter | 21″ |
| Sidewall height | 130 mm |
| Circumference | 98.1″ |
| Revolutions per mile | 645.7 |
Wheels
What rims fit 325/40 R21 tires?
A tire fits a range of rim widths. Too narrow or too wide and the sidewall changes shape.
Minimum
9″
Ideal
10″
Maximum
11.5″
Rim diameter is fixed at 21″ — only the width varies. Estimated from the 12.8″ section width (70–90% rule).
Fitted from the factory on rims: 21x11.5.
Sidewall
325/40 R21 — what does it mean?
| Parameter | Meaning |
|---|---|
| 325 | The first number is the section width — 325 mm, or about 12.8 inches across the widest part of the tire. |
| 40 | The second number is the aspect ratio: sidewall height as a percentage of width. At 40%, the sidewall is about 130 mm tall. |
| R21 | R means radial construction, which nearly all modern tires use. The number is the rim diameter in inches — this tire fits a 21-inch wheel. |