315/30R21 tire size
315/30R21 is a metric size: 28.4" tall, 12.4" wide, on a 21" rim — about a 28.5x12.50R21. The sidewall is 3.7" and the tire turns 709 times per mile.
315/30R21 specs
| Overall diameter (height) | 28.44" · 722 mm |
|---|---|
| Section width | 12.40" · 315 mm |
| Sidewall height | 3.72" · 95 mm (30% of width) |
| Rim diameter | 21" |
| Circumference | 89.35" · 2.269 m |
| Revolutions per mile | 709 (441 per km) |
| Inch (flotation) equivalent | 28.5x12.50R21 |
Equivalent sizes on a 21" rim
Sizes within ±5% of the overall diameter. Green rows are inside the usual ±3% limit for keeping the speedometer, ABS and gearing right; red rows are bigger changes that need clearance checks.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 265/40R21 common | 29.35" | +3.18% | -50 mm | 61.9 mph | compare → |
| 275/35R21 common | 28.58" | +0.48% | -40 mm | 60.3 mph | compare → |
| 295/35R21 | 29.13" | +2.42% | -20 mm | 61.5 mph | compare → |
| 255/40R21 | 29.03" | +2.08% | -60 mm | 61.2 mph | compare → |
| 265/35R21 | 28.30" | -0.48% | -50 mm | 59.7 mph | compare → |
| 245/35R21 | 27.75" | -2.42% | -70 mm | 58.5 mph | compare → |
| 325/30R21 | 28.68" | +0.83% | +10 mm | 60.5 mph | compare → |
| 275/40R21 | 29.66" | +4.29% | -40 mm | 62.6 mph | compare → |
| 255/35R21 | 28.03" | -1.45% | -60 mm | 59.1 mph | compare → |
| 285/35R21 | 28.85" | +1.45% | -30 mm | 60.9 mph | compare → |
| 245/40R21 | 28.72" | +0.97% | -70 mm | 60.6 mph | compare → |
| 315/35R21 | 29.68" | +4.36% | 0 mm | 62.6 mph | compare → |
| 305/30R21 | 28.20" | -0.83% | -10 mm | 59.5 mph | compare → |
| 295/30R21 | 27.97" | -1.66% | -20 mm | 59.0 mph | compare → |
| 285/30R21 | 27.73" | -2.49% | -30 mm | 58.5 mph | compare → |
| 275/30R21 | 27.50" | -3.32% | -40 mm | 58.0 mph | compare → |
| 245/45R21 | 29.68" | +4.36% | -70 mm | 62.6 mph | compare → |
| 255/30R21 | 27.02" | -4.98% | -60 mm | 57.0 mph | calculate → |
| 355/25R21 | 27.99" | -1.59% | +40 mm | 59.0 mph | calculate → |
| 235/45R21 | 29.33" | +3.11% | -80 mm | 61.9 mph | calculate → |
| 335/30R21 | 28.91" | +1.66% | +20 mm | 61.0 mph | calculate → |
| 305/35R21 | 29.41" | +3.39% | -10 mm | 62.0 mph | calculate → |
| 345/30R21 | 29.15" | +2.49% | +30 mm | 61.5 mph | calculate → |
| 265/30R21 | 27.26" | -4.15% | -50 mm | 57.5 mph | calculate → |
| 225/45R21 | 28.97" | +1.87% | -90 mm | 61.1 mph | calculate → |
| 345/25R21 | 27.79" | -2.28% | +30 mm | 58.6 mph | calculate → |
| 325/25R21 | 27.40" | -3.67% | +10 mm | 57.8 mph | calculate → |
Plus / minus sizing: 20" and 22" rims
Same overall height on a different rim. Check wheel width and clearance before switching.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 245/45R20 common | 28.68" | +0.84% | -70 mm | 60.5 mph | compare → |
| 275/40R20 common | 28.66" | +0.78% | -40 mm | 60.5 mph | compare → |
| 315/35R20 common | 28.68" | +0.84% | 0 mm | 60.5 mph | compare → |
| 305/35R20 | 28.41" | -0.12% | -10 mm | 59.9 mph | compare → |
| 235/45R20 | 28.33" | -0.40% | -80 mm | 59.8 mph | compare → |
| 265/40R20 | 28.35" | -0.33% | -50 mm | 59.8 mph | compare → |
| 265/30R22 | 28.26" | -0.64% | -50 mm | 59.6 mph | compare → |
| 335/25R22 | 28.59" | +0.54% | +20 mm | 60.3 mph | calculate → |
| 315/25R22 | 28.20" | -0.84% | 0 mm | 59.5 mph | calculate → |
| 275/30R22 | 28.50" | +0.19% | -40 mm | 60.1 mph | calculate → |
| 195/55R20 | 28.44" | +0.01% | -120 mm | 60.0 mph | calculate → |
Try another size against 315/30R21
Questions
What size is 315/30R21 in inches?
315/30R21 is about 28.4" tall and 12.4" wide on a 21-inch rim — roughly a 28.5x12.50R21 in inch sizing.
What does 315/30R21 mean?
315 mm section width, sidewall 30% of the width (3.72"), radial construction, 21-inch rim.
What tire sizes are equivalent to 315/30R21?
On the same 21" rim, within 3% of the diameter: 265/35R21 (-0.48%), 275/35R21 (+0.48%), 305/30R21 (-0.83%), 325/30R21 (+0.83%), 245/40R21 (+0.97%), 255/35R21 (-1.45%).
How many revolutions per mile does a 315/30R21 tire make?
About 709 revolutions per mile (circumference 89.3").
How these numbers are computed
Diameter = rim + 2 × sidewall, sidewall = width × aspect ÷ 100, circumference = π × diameter, revolutions per mile = 63,360 ÷ circumference. Real tires differ by brand by a few tenths of an inch. Last reviewed October 14, 2026.