305/55R21 tire size in inches
A 305/55R21 tire measures
34.2" tall × 12.0" wide
6.60" sidewall on a 21" wheel. 590 revolutions per mile.
305/55R21 means a tire 305 mm wide, with sidewalls 55% as tall as the tire is wide (168 mm), radial construction (R), for a 21 inch wheel.
305/55R21 specs
| Overall diameter (height) | 34.21 inches (869 mm) |
|---|---|
| Section width | 12.01 inches (305 mm) |
| Sidewall height | 6.60 inches (168 mm) |
| Wheel (rim) diameter | 21 inches |
| Circumference | 107.5 inches (2,730 mm) |
| Revolutions per mile | 590 |
| Revolutions per kilometer | 366 |
| Approximate rim width | 9.0" to 10.5" |
| In inches (flotation style) | 34.2x12.0R21 |
| Aspect ratio | 55% |
Calculated from the size. Real tires differ by brand, model and tread depth, typically by a few tenths of an inch.
Sizes that can replace 305/55R21 on a 21" wheel
These 21" sizes are within 3% of 305/55R21's overall diameter, the range most tire shops treat as interchangeable.
| Size | Diameter | Width | Difference | Real speed at 60 | |
|---|---|---|---|---|---|
| 335/50R21 | 34.19" | 13.19" | −0.1% | 60.0 mph | Compare |
| 345/50R21 | 34.58" | 13.58" | +1.1% | 60.7 mph | Compare |
| 325/50R21 | 33.80" | 12.80" | −1.2% | 59.3 mph | Compare |
| 295/55R21 | 33.78" | 11.61" | −1.3% | 59.2 mph | Compare |
| 315/55R21 | 34.64" | 12.40" | +1.3% | 60.8 mph | Compare |
| 355/45R21 | 33.58" | 13.98" | −1.8% | 58.9 mph | Compare |
| 355/50R21 | 34.98" | 13.98" | +2.2% | 61.3 mph | Compare |
| 315/50R21 | 33.40" | 12.40" | −2.4% | 58.6 mph | Compare |
| 325/55R21 | 35.07" | 12.80" | +2.5% | 61.5 mph | Compare |
| 285/55R21 | 33.34" | 11.22" | −2.5% | 58.5 mph | Compare |
| 345/45R21 | 33.22" | 13.58" | −2.9% | 58.3 mph | Compare |
Same height on other wheel sizes (plus and minus sizing)
| Size | Wheel | Diameter | Difference | |
|---|---|---|---|---|
| 345/45R22 | 22" | 34.22" | 0.0% | Compare |
| 325/40R24 | 24" | 34.24" | +0.1% | Compare |
| 275/75R18 | 18" | 34.24" | +0.1% | Compare |
| 295/70R18 | 18" | 34.26" | +0.1% | Compare |
| 315/65R18 | 18" | 34.12" | −0.3% | Compare |
| 295/65R19 | 19" | 34.10" | −0.3% | Compare |
| 285/55R22 | 22" | 34.34" | +0.4% | Compare |
| 275/65R20 | 20" | 34.07" | −0.4% | Compare |
| 285/85R15 | 15" | 34.07" | −0.4% | Compare |
| 325/55R20 | 20" | 34.07" | −0.4% | Compare |
| 325/60R19 | 19" | 34.35" | +0.4% | Compare |
| 315/70R17 | 17" | 34.36" | +0.4% | Compare |
One size up or down
Compare 305/55R21 with another size
Questions
- How tall is a 305/55R21 tire?
- A 305/55R21 tire is 34.2 inches tall (869 mm), calculated from the size. It is 12.0 inches wide with 6.6 inches sidewalls. Real tires vary by a few tenths of an inch between brands and tread patterns.
- What does 305/55R21 mean?
- 305/55R21 means a tire 305 mm wide, with sidewalls 55% as tall as the tire is wide (168 mm), radial construction (R), for a 21 inch wheel.
- How many revolutions per mile does a 305/55R21 tire make?
- About 590 revolutions per mile, based on a circumference of 107.5 inches. Under load the tire flattens slightly, so the maker's published figure is usually a little higher.
- What rim width fits a 305/55R21 tire?
- Roughly 9.0" to 10.5". Check the tire maker's approved rim range for the exact model before buying wheels.
- Can I use 335/50R21 instead of 305/55R21?
- 335/50R21 is −0.02 inches (−0.1%) in overall diameter, so at an indicated 60 mph you would be doing 60.0 mph. Differences under 3% are usually fine, but check clearance, load index and your vehicle's placard.