205/40R18 tire size
205/40R18 is a metric size: 24.5" tall, 8.1" wide, on a 18" rim — about a 24.5x8.00R18. The sidewall is 3.2" and the tire turns 825 times per mile.
205/40R18 specs
| Overall diameter (height) | 24.46" · 621 mm |
|---|---|
| Section width | 8.07" · 205 mm |
| Sidewall height | 3.23" · 82 mm (40% of width) |
| Rim diameter | 18" |
| Circumference | 76.83" · 1.952 m |
| Revolutions per mile | 825 (512 per km) |
| Inch (flotation) equivalent | 24.5x8.00R18 |
Equivalent sizes on a 18" 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 | |
|---|---|---|---|---|---|
| 225/40R18 common | 25.09" | +2.58% | +20 mm | 61.5 mph | compare → |
| 235/40R18 common | 25.40" | +3.86% | +30 mm | 62.3 mph | compare → |
| 255/35R18 common | 25.03" | +2.33% | +50 mm | 61.4 mph | compare → |
| 275/35R18 common | 25.58" | +4.59% | +70 mm | 62.8 mph | compare → |
| 265/35R18 common | 25.30" | +3.46% | +60 mm | 62.1 mph | compare → |
| 215/45R18 common | 25.62" | +4.75% | +10 mm | 62.8 mph | compare → |
| 245/35R18 common | 24.75" | +1.21% | +40 mm | 60.7 mph | compare → |
| 215/40R18 | 24.77" | +1.29% | +10 mm | 60.8 mph | compare → |
| 295/30R18 | 24.97" | +2.09% | +90 mm | 61.3 mph | compare → |
| 285/30R18 | 24.73" | +1.13% | +80 mm | 60.7 mph | compare → |
| 315/30R18 | 25.44" | +4.02% | +110 mm | 62.4 mph | compare → |
| 225/35R18 | 24.20" | -1.05% | +20 mm | 59.4 mph | calculate → |
| 215/35R18 | 23.93" | -2.17% | +10 mm | 58.7 mph | calculate → |
| 235/35R18 | 24.48" | +0.08% | +30 mm | 60.0 mph | calculate → |
| 305/30R18 | 25.20" | +3.06% | +100 mm | 61.8 mph | calculate → |
| 205/35R18 | 23.65" | -3.30% | 0 mm | 58.0 mph | calculate → |
| 155/60R18 | 25.32" | +3.54% | -50 mm | 62.1 mph | calculate → |
| 235/30R18 | 23.55" | -3.70% | +30 mm | 57.8 mph | calculate → |
| 205/45R18 | 25.26" | +3.30% | 0 mm | 62.0 mph | calculate → |
Plus / minus sizing: 17" and 19" rims
Same overall height on a different rim. Check wheel width and clearance before switching.
| Size | Diameter | Difference | Width | Speedo at 60 | |
|---|---|---|---|---|---|
| 215/45R17 common | 24.62" | +0.66% | +10 mm | 60.4 mph | compare → |
| 205/45R17 common | 24.26" | -0.79% | 0 mm | 59.5 mph | compare → |
| 235/40R17 | 24.40" | -0.23% | +30 mm | 59.9 mph | compare → |
| 275/35R17 | 24.58" | +0.50% | +70 mm | 60.3 mph | calculate → |
| 235/30R19 | 24.55" | +0.39% | +30 mm | 60.2 mph | calculate → |
Try another size against 205/40R18
Questions
What size is 205/40R18 in inches?
205/40R18 is about 24.5" tall and 8.1" wide on a 18-inch rim — roughly a 24.5x8.00R18 in inch sizing.
What does 205/40R18 mean?
205 mm section width, sidewall 40% of the width (3.23"), radial construction, 18-inch rim.
What tire sizes are equivalent to 205/40R18?
On the same 18" rim, within 3% of the diameter: 235/35R18 (+0.08%), 225/35R18 (-1.05%), 285/30R18 (+1.13%), 245/35R18 (+1.21%), 215/40R18 (+1.29%), 295/30R18 (+2.09%).
How many revolutions per mile does a 205/40R18 tire make?
About 825 revolutions per mile (circumference 76.8").
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.