305/45R21 tire size in inches
A 305/45R21 tire measures
31.8" tall × 12.0" wide
5.40" sidewall on a 21" wheel. 634 revolutions per mile.
305/45R21 means a tire 305 mm wide, with sidewalls 45% as tall as the tire is wide (137 mm), radial construction (R), for a 21 inch wheel.
305/45R21 specs
| Overall diameter (height) | 31.81 inches (808 mm) |
|---|---|
| Section width | 12.01 inches (305 mm) |
| Sidewall height | 5.40 inches (137 mm) |
| Wheel (rim) diameter | 21 inches |
| Circumference | 99.9 inches (2,538 mm) |
| Revolutions per mile | 634 |
| Revolutions per kilometer | 394 |
| Approximate rim width | 10.0" to 11.5" |
| In inches (flotation style) | 31.8x12.0R21 |
| Aspect ratio | 45% |
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 305/45R21 on a 21" wheel
These 21" sizes are within 3% of 305/45R21's overall diameter, the range most tire shops treat as interchangeable.
| Size | Diameter | Width | Difference | Real speed at 60 | |
|---|---|---|---|---|---|
| 275/50R21 | 31.83" | 10.83" | +0.1% | 60.0 mph | Compare |
| 345/40R21 | 31.87" | 13.58" | +0.2% | 60.1 mph | Compare |
| 245/55R21 | 31.61" | 9.65" | −0.6% | 59.6 mph | Compare |
| 255/55R21 | 32.04" | 10.04" | +0.7% | 60.4 mph | Compare |
| 335/40R21 | 31.55" | 13.19" | −0.8% | 59.5 mph | Compare |
| 315/45R21 | 32.16" | 12.40" | +1.1% | 60.7 mph | Compare |
| 295/45R21 | 31.45" | 11.61" | −1.1% | 59.3 mph | Compare |
| 265/50R21 | 31.43" | 10.43" | −1.2% | 59.3 mph | Compare |
| 355/40R21 | 32.18" | 13.98" | +1.2% | 60.7 mph | Compare |
| 285/50R21 | 32.22" | 11.22" | +1.3% | 60.8 mph | Compare |
| 325/40R21 | 31.24" | 12.80" | −1.8% | 58.9 mph | Compare |
| 235/55R21 | 31.18" | 9.25" | −2.0% | 58.8 mph | Compare |
Same height on other wheel sizes (plus and minus sizing)
| Size | Wheel | Diameter | Difference | |
|---|---|---|---|---|
| 325/50R19 | 19" | 31.80" | 0.0% | Compare |
| 285/75R15 | 15" | 31.83" | +0.1% | Compare |
| 355/35R22 | 22" | 31.78" | −0.1% | Compare |
| 295/55R19 | 19" | 31.78" | −0.1% | Compare |
| 285/35R24 | 24" | 31.85" | +0.1% | Compare |
| 275/45R22 | 22" | 31.74" | −0.2% | Compare |
| 335/45R20 | 20" | 31.87" | +0.2% | Compare |
| 235/75R18 | 18" | 31.88" | +0.2% | Compare |
| 265/85R14 | 14" | 31.74" | −0.2% | Compare |
| 315/60R17 | 17" | 31.88" | +0.2% | Compare |
| 235/85R16 | 16" | 31.73" | −0.2% | Compare |
| 285/70R16 | 16" | 31.71" | −0.3% | Compare |
One size up or down
- 295/45R21narrower: 31.5" × 11.6"
- 315/45R21wider: 32.2" × 12.4"
- 305/40R21lower profile: 30.6" × 12.0"
- 305/50R21taller sidewall: 33.0" × 12.0"
Compare 305/45R21 with another size
Questions
- How tall is a 305/45R21 tire?
- A 305/45R21 tire is 31.8 inches tall (808 mm), calculated from the size. It is 12.0 inches wide with 5.4 inches sidewalls. Real tires vary by a few tenths of an inch between brands and tread patterns.
- What does 305/45R21 mean?
- 305/45R21 means a tire 305 mm wide, with sidewalls 45% as tall as the tire is wide (137 mm), radial construction (R), for a 21 inch wheel.
- How many revolutions per mile does a 305/45R21 tire make?
- About 634 revolutions per mile, based on a circumference of 99.9 inches. Under load the tire flattens slightly, so the maker's published figure is usually a little higher.
- What rim width fits a 305/45R21 tire?
- Roughly 10.0" to 11.5". Check the tire maker's approved rim range for the exact model before buying wheels.
- Can I use 275/50R21 instead of 305/45R21?
- 275/50R21 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.