315/40R21 tire size in inches
A 315/40R21 tire measures
30.9" tall × 12.4" wide
4.96" sidewall on a 21" wheel. 652 revolutions per mile.
315/40R21 means a tire 315 mm wide, with sidewalls 40% as tall as the tire is wide (126 mm), radial construction (R), for a 21 inch wheel.
315/40R21 specs
| Overall diameter (height) | 30.92 inches (785 mm) |
|---|---|
| Section width | 12.40 inches (315 mm) |
| Sidewall height | 4.96 inches (126 mm) |
| Wheel (rim) diameter | 21 inches |
| Circumference | 97.1 inches (2,467 mm) |
| Revolutions per mile | 652 |
| Revolutions per kilometer | 405 |
| Approximate rim width | 10.5" to 12.0" |
| In inches (flotation style) | 30.9x12.4R21 |
| 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 315/40R21 on a 21" wheel
These 21" sizes are within 3% of 315/40R21's overall diameter, the range most tire shops treat as interchangeable.
| Size | Diameter | Width | Difference | Real speed at 60 | |
|---|---|---|---|---|---|
| 255/50R21 | 31.04" | 10.04" | +0.4% | 60.2 mph | Compare |
| 355/35R21 | 30.78" | 13.98" | −0.4% | 59.7 mph | Compare |
| 225/55R21 | 30.74" | 8.86" | −0.6% | 59.7 mph | Compare |
| 275/45R21 | 30.74" | 10.83" | −0.6% | 59.7 mph | Compare |
| 285/45R21 | 31.10" | 11.22" | +0.6% | 60.3 mph | Compare |
| 235/55R21 | 31.18" | 9.25" | +0.8% | 60.5 mph | Compare |
| 245/50R21 | 30.65" | 9.65" | −0.9% | 59.5 mph | Compare |
| 305/40R21 | 30.61" | 12.01" | −1.0% | 59.4 mph | Compare |
| 325/40R21 | 31.24" | 12.80" | +1.0% | 60.6 mph | Compare |
| 345/35R21 | 30.51" | 13.58" | −1.3% | 59.2 mph | Compare |
| 265/50R21 | 31.43" | 10.43" | +1.7% | 61.0 mph | Compare |
| 265/45R21 | 30.39" | 10.43" | −1.7% | 59.0 mph | Compare |
Same height on other wheel sizes (plus and minus sizing)
| Size | Wheel | Diameter | Difference | |
|---|---|---|---|---|
| 275/55R19 | 19" | 30.91" | 0.0% | Compare |
| 295/60R17 | 17" | 30.94" | +0.1% | Compare |
| 235/70R18 | 18" | 30.95" | +0.1% | Compare |
| 325/35R22 | 22" | 30.96" | +0.1% | Compare |
| 235/75R17 | 17" | 30.88" | −0.1% | Compare |
| 295/30R24 | 24" | 30.97" | +0.2% | Compare |
| 335/45R19 | 19" | 30.87" | −0.2% | Compare |
| 285/40R22 | 22" | 30.98" | +0.2% | Compare |
| 345/40R20 | 20" | 30.87" | −0.2% | Compare |
| 355/25R24 | 24" | 30.99" | +0.2% | Compare |
| 275/60R18 | 18" | 30.99" | +0.2% | Compare |
| 31x10.50R15 | 15" | 31.00" | +0.3% | Compare |
One size up or down
- 305/40R21narrower: 30.6" × 12.0"
- 325/40R21wider: 31.2" × 12.8"
- 315/35R21lower profile: 29.7" × 12.4"
- 315/45R21taller sidewall: 32.2" × 12.4"
Compare 315/40R21 with another size
Questions
- How tall is a 315/40R21 tire?
- A 315/40R21 tire is 30.9 inches tall (785 mm), calculated from the size. It is 12.4 inches wide with 5.0 inches sidewalls. Real tires vary by a few tenths of an inch between brands and tread patterns.
- What does 315/40R21 mean?
- 315/40R21 means a tire 315 mm wide, with sidewalls 40% as tall as the tire is wide (126 mm), radial construction (R), for a 21 inch wheel.
- How many revolutions per mile does a 315/40R21 tire make?
- About 652 revolutions per mile, based on a circumference of 97.1 inches. Under load the tire flattens slightly, so the maker's published figure is usually a little higher.
- What rim width fits a 315/40R21 tire?
- Roughly 10.5" to 12.0". Check the tire maker's approved rim range for the exact model before buying wheels.
- Can I use 255/50R21 instead of 315/40R21?
- 255/50R21 is +0.12 inches (+0.4%) in overall diameter, so at an indicated 60 mph you would be doing 60.2 mph. Differences under 3% are usually fine, but check clearance, load index and your vehicle's placard.