325/40R21 tire size in inches
A 325/40R21 tire measures
31.2" tall × 12.8" wide
5.12" sidewall on a 21" wheel. 646 revolutions per mile.
325/40R21 means a tire 325 mm wide, with sidewalls 40% as tall as the tire is wide (130 mm), radial construction (R), for a 21 inch wheel.
325/40R21 specs
| Overall diameter (height) | 31.24 inches (793 mm) |
|---|---|
| Section width | 12.80 inches (325 mm) |
| Sidewall height | 5.12 inches (130 mm) |
| Wheel (rim) diameter | 21 inches |
| Circumference | 98.1 inches (2,493 mm) |
| Revolutions per mile | 646 |
| Revolutions per kilometer | 401 |
| Approximate rim width | 10.5" to 12.0" |
| In inches (flotation style) | 31.2x12.8R21 |
| 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 325/40R21 on a 21" wheel
These 21" sizes are within 3% of 325/40R21's overall diameter, the range most tire shops treat as interchangeable.
| Size | Diameter | Width | Difference | Real speed at 60 | |
|---|---|---|---|---|---|
| 235/55R21 | 31.18" | 9.25" | −0.2% | 59.9 mph | Compare |
| 285/45R21 | 31.10" | 11.22" | −0.4% | 59.7 mph | Compare |
| 265/50R21 | 31.43" | 10.43" | +0.6% | 60.4 mph | Compare |
| 255/50R21 | 31.04" | 10.04" | −0.6% | 59.6 mph | Compare |
| 295/45R21 | 31.45" | 11.61" | +0.7% | 60.4 mph | Compare |
| 335/40R21 | 31.55" | 13.19" | +1.0% | 60.6 mph | Compare |
| 315/40R21 | 30.92" | 12.40" | −1.0% | 59.4 mph | Compare |
| 245/55R21 | 31.61" | 9.65" | +1.2% | 60.7 mph | Compare |
| 355/35R21 | 30.78" | 13.98" | −1.4% | 59.1 mph | Compare |
| 225/55R21 | 30.74" | 8.86" | −1.6% | 59.1 mph | Compare |
| 275/45R21 | 30.74" | 10.83" | −1.6% | 59.1 mph | Compare |
| 305/45R21 | 31.81" | 12.01" | +1.8% | 61.1 mph | Compare |
Same height on other wheel sizes (plus and minus sizing)
| Size | Wheel | Diameter | Difference | |
|---|---|---|---|---|
| 275/75R15 | 15" | 31.24" | 0.0% | Compare |
| 335/35R22 | 22" | 31.23" | 0.0% | Compare |
| 345/45R19 | 19" | 31.22" | 0.0% | Compare |
| 235/50R22 | 22" | 31.25" | +0.1% | Compare |
| 285/50R20 | 20" | 31.22" | −0.1% | Compare |
| 305/55R18 | 18" | 31.21" | −0.1% | Compare |
| 305/30R24 | 24" | 31.20" | −0.1% | Compare |
| 335/50R18 | 18" | 31.19" | −0.2% | Compare |
| 225/75R18 | 18" | 31.29" | +0.2% | Compare |
| 295/40R22 | 22" | 31.29" | +0.2% | Compare |
| 355/40R20 | 20" | 31.18" | −0.2% | Compare |
| 265/35R24 | 24" | 31.30" | +0.2% | Compare |
One size up or down
- 315/40R21narrower: 30.9" × 12.4"
- 335/40R21wider: 31.6" × 13.2"
- 325/35R21lower profile: 30.0" × 12.8"
- 325/45R21taller sidewall: 32.5" × 12.8"
Compare 325/40R21 with another size
Questions
- How tall is a 325/40R21 tire?
- A 325/40R21 tire is 31.2 inches tall (793 mm), calculated from the size. It is 12.8 inches wide with 5.1 inches sidewalls. Real tires vary by a few tenths of an inch between brands and tread patterns.
- What does 325/40R21 mean?
- 325/40R21 means a tire 325 mm wide, with sidewalls 40% as tall as the tire is wide (130 mm), radial construction (R), for a 21 inch wheel.
- How many revolutions per mile does a 325/40R21 tire make?
- About 646 revolutions per mile, based on a circumference of 98.1 inches. Under load the tire flattens slightly, so the maker's published figure is usually a little higher.
- What rim width fits a 325/40R21 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 235/55R21 instead of 325/40R21?
- 235/55R21 is −0.06 inches (−0.2%) 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.