177Best 305/40 R21 tires
1 rated tire available in this size, scored on dry, wet, snow, comfort and wear. Top overall right now is the Pirelli Scorpion Winter 2 at 77/100.
30.6″
overall diameter
12″
section width
21″
rim diameter
659
revs per mile
More top-rated 305/40 R21 tires
1177Conversion
305/40 R21 in inches
| Overall diameter | 30.6″ |
| Section width | 12″ |
| Rim diameter | 21″ |
| Sidewall height | 122 mm |
| Circumference | 96.2″ |
| Revolutions per mile | 659 |
Wheels
What rims fit 305/40 R21 tires?
A tire fits a range of rim widths. Too narrow or too wide and the sidewall changes shape.
Minimum
8.5″
Ideal
9.5″
Maximum
11″
Rim diameter is fixed at 21″ — only the width varies. Estimated from the 12″ section width (70–90% rule).
Fitted from the factory on rims: 21x11.
Sidewall
305/40 R21 — what does it mean?
| Parameter | Meaning |
|---|---|
| 305 | The first number is the section width — 305 mm, or about 12 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 122 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. |