345/40R21 tire size in inches
A 345/40R21 tire measures
31.9" tall × 13.6" wide
5.43" sidewall on a 21" wheel. 633 revolutions per mile.
345/40R21 means a tire 345 mm wide, with sidewalls 40% as tall as the tire is wide (138 mm), radial construction (R), for a 21 inch wheel.
345/40R21 specs
| Overall diameter (height) | 31.87 inches (809 mm) |
|---|---|
| Section width | 13.58 inches (345 mm) |
| Sidewall height | 5.43 inches (138 mm) |
| Wheel (rim) diameter | 21 inches |
| Circumference | 100.1 inches (2,543 mm) |
| Revolutions per mile | 633 |
| Revolutions per kilometer | 393 |
| Approximate rim width | 11.5" to 13.0" |
| In inches (flotation style) | 31.9x13.6R21 |
| Aspect ratio | 40% |
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 345/40R21 on a 21" wheel
These 21" sizes are within 3% of 345/40R21'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% | 59.9 mph | Compare |
| 305/45R21 | 31.81" | 12.01" | −0.2% | 59.9 mph | Compare |
| 255/55R21 | 32.04" | 10.04" | +0.6% | 60.3 mph | Compare |
| 245/55R21 | 31.61" | 9.65" | −0.8% | 59.5 mph | Compare |
| 315/45R21 | 32.16" | 12.40" | +0.9% | 60.6 mph | Compare |
| 335/40R21 | 31.55" | 13.19" | −1.0% | 59.4 mph | Compare |
| 355/40R21 | 32.18" | 13.98" | +1.0% | 60.6 mph | Compare |
| 285/50R21 | 32.22" | 11.22" | +1.1% | 60.7 mph | Compare |
| 295/45R21 | 31.45" | 11.61" | −1.3% | 59.2 mph | Compare |
| 265/50R21 | 31.43" | 10.43" | −1.4% | 59.2 mph | Compare |
| 265/55R21 | 32.48" | 10.43" | +1.9% | 61.1 mph | Compare |
| 325/40R21 | 31.24" | 12.80" | −2.0% | 58.8 mph | Compare |
Same height on other wheel sizes (plus and minus sizing)
| Size | Wheel | Diameter | Difference | |
|---|---|---|---|---|
| 335/45R20 | 20" | 31.87" | 0.0% | Compare |
| 235/75R18 | 18" | 31.88" | 0.0% | Compare |
| 285/35R24 | 24" | 31.85" | 0.0% | Compare |
| 315/60R17 | 17" | 31.88" | 0.0% | Compare |
| 285/75R15 | 15" | 31.83" | −0.1% | Compare |
| 275/55R20 | 20" | 31.91" | +0.1% | Compare |
| 335/30R24 | 24" | 31.91" | +0.1% | Compare |
| 315/40R22 | 22" | 31.92" | +0.2% | Compare |
| 295/60R18 | 18" | 31.94" | +0.2% | Compare |
| 325/50R19 | 19" | 31.80" | −0.2% | Compare |
| 355/35R22 | 22" | 31.78" | −0.3% | Compare |
| 295/55R19 | 19" | 31.78" | −0.3% | Compare |
One size up or down
- 335/40R21narrower: 31.6" × 13.2"
- 355/40R21wider: 32.2" × 14.0"
- 345/35R21lower profile: 30.5" × 13.6"
- 345/45R21taller sidewall: 33.2" × 13.6"
Compare 345/40R21 with another size
Questions
- How tall is a 345/40R21 tire?
- A 345/40R21 tire is 31.9 inches tall (809 mm), calculated from the size. It is 13.6 inches wide with 5.4 inches sidewalls. Real tires vary by a few tenths of an inch between brands and tread patterns.
- What does 345/40R21 mean?
- 345/40R21 means a tire 345 mm wide, with sidewalls 40% as tall as the tire is wide (138 mm), radial construction (R), for a 21 inch wheel.
- How many revolutions per mile does a 345/40R21 tire make?
- About 633 revolutions per mile, based on a circumference of 100.1 inches. Under load the tire flattens slightly, so the maker's published figure is usually a little higher.
- What rim width fits a 345/40R21 tire?
- Roughly 11.5" to 13.0". Check the tire maker's approved rim range for the exact model before buying wheels.
- Can I use 275/50R21 instead of 345/40R21?
- 275/50R21 is −0.04 inches (−0.1%) in overall diameter, so at an indicated 60 mph you would be doing 59.9 mph. Differences under 3% are usually fine, but check clearance, load index and your vehicle's placard.