31x18.00R20 tire size
31x18.00R20 is a flotation (inch) size: 31.0" tall, 18.0" wide, on a 20" rim — about a 460/30R20. The sidewall is 5.5" and the tire turns 651 times per mile.
31x18.00R20 specs
| Overall diameter (height) | 31.00" · 787 mm |
|---|---|
| Section width | 18.00" · 457 mm |
| Sidewall height | 5.50" · 140 mm (31% of width) |
| Rim diameter | 20" |
| Circumference | 97.39" · 2.474 m |
| Revolutions per mile | 651 (404 per km) |
| Closest metric size | 460/30R20 |
Equivalent sizes on a 20" 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 | |
|---|---|---|---|---|---|
| 275/55R20 common | 31.91" | +2.93% | -182 mm | 61.8 mph | calculate → |
| 255/50R20 common | 30.04" | -3.10% | -202 mm | 58.1 mph | calculate → |
| 265/50R20 common | 30.43" | -1.83% | -192 mm | 58.9 mph | calculate → |
| 245/50R20 common | 29.65" | -4.37% | -212 mm | 57.4 mph | calculate → |
| 275/45R20 common | 29.74" | -4.05% | -182 mm | 57.6 mph | calculate → |
| 255/55R20 common | 31.04" | +0.14% | -202 mm | 60.1 mph | calculate → |
| 235/55R20 common | 30.18" | -2.65% | -222 mm | 58.4 mph | calculate → |
| 265/60R20 common | 32.52" | +4.90% | -192 mm | 62.9 mph | calculate → |
| 285/55R20 common | 32.34" | +4.33% | -172 mm | 62.6 mph | calculate → |
| 275/50R20 common | 30.83" | -0.56% | -182 mm | 59.7 mph | calculate → |
| 285/50R20 | 31.22" | +0.71% | -172 mm | 60.4 mph | calculate → |
| 245/60R20 | 31.57" | +1.85% | -212 mm | 61.1 mph | calculate → |
| 285/45R20 | 30.10" | -2.91% | -172 mm | 58.3 mph | calculate → |
| 305/50R20 | 32.01" | +3.25% | -152 mm | 62.0 mph | calculate → |
| 295/45R20 | 30.45" | -1.77% | -162 mm | 58.9 mph | calculate → |
| 305/40R20 | 29.61" | -4.50% | -152 mm | 57.3 mph | calculate → |
| 255/60R20 | 32.05" | +3.38% | -202 mm | 62.0 mph | calculate → |
| 235/60R20 | 31.10" | +0.33% | -222 mm | 60.2 mph | calculate → |
| 305/45R20 | 30.81" | -0.62% | -152 mm | 59.6 mph | calculate → |
| 265/55R20 | 31.48" | +1.54% | -192 mm | 60.9 mph | calculate → |
| 295/50R20 | 31.61" | +1.98% | -162 mm | 61.2 mph | calculate → |
| 175/70R20 | 29.65" | -4.37% | -282 mm | 57.4 mph | calculate → |
| 315/50R20 | 32.40" | +4.52% | -142 mm | 62.7 mph | calculate → |
Plus / minus sizing: 19" and 21" rims
Same overall height on a different rim. Check wheel width and clearance before switching.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 255/60R19 common | 31.05" | +0.15% | -202 mm | 60.1 mph | calculate → |
| 275/45R21 | 30.74" | -0.83% | -182 mm | 59.5 mph | calculate → |
| 285/45R21 | 31.10" | +0.32% | -172 mm | 60.2 mph | calculate → |
| 275/55R19 | 30.91" | -0.29% | -182 mm | 59.8 mph | calculate → |
| 315/40R21 | 30.92" | -0.25% | -142 mm | 59.8 mph | calculate → |
| 255/50R21 | 31.04" | +0.13% | -202 mm | 60.1 mph | calculate → |
| 235/65R19 | 31.03" | +0.09% | -222 mm | 60.1 mph | calculate → |
| 325/40R21 | 31.24" | +0.76% | -132 mm | 60.5 mph | calculate → |
| 165/90R19 | 30.69" | -0.99% | -292 mm | 59.4 mph | calculate → |
Try another size against 31x18.00R20
Questions
What size is 31x18.00R20 in inches?
31x18.00R20 is about 31.0" tall and 18.0" wide on a 20-inch rim — roughly a 460/30R20 in inch sizing.
What does 31x18.00R20 mean?
31" overall diameter, 18.00" section width, radial, 20" rim.
What tire sizes are equivalent to 31x18.00R20?
On the same 20" rim, within 3% of the diameter: 255/55R20 (+0.14%), 235/60R20 (+0.33%), 275/50R20 (-0.56%), 305/45R20 (-0.62%), 285/50R20 (+0.71%), 265/55R20 (+1.54%).
How many revolutions per mile does a 31x18.00R20 tire make?
About 651 revolutions per mile (circumference 97.4").
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.