225/40R18 tire size
225/40R18 is a metric size: 25.1" tall, 8.9" wide, on a 18" rim — about a 25x9.00R18. The sidewall is 3.5" and the tire turns 804 times per mile.
225/40R18 specs
| Overall diameter (height) | 25.09" · 637 mm |
|---|---|
| Section width | 8.86" · 225 mm |
| Sidewall height | 3.54" · 90 mm (40% of width) |
| Rim diameter | 18" |
| Circumference | 78.81" · 2.002 m |
| Revolutions per mile | 804 (500 per km) |
| Inch (flotation) equivalent | 25x9.00R18 |
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 | |
|---|---|---|---|---|---|
| 245/40R18 common | 25.72" | +2.51% | +20 mm | 61.5 mph | compare → |
| 225/45R18 common | 25.97" | +3.53% | 0 mm | 62.1 mph | compare → |
| 235/45R18 common | 26.33" | +4.94% | +10 mm | 63.0 mph | compare → |
| 235/40R18 common | 25.40" | +1.26% | +10 mm | 60.8 mph | compare → |
| 255/35R18 common | 25.03" | -0.24% | +30 mm | 59.9 mph | compare → |
| 255/40R18 common | 26.03" | +3.77% | +30 mm | 62.3 mph | compare → |
| 275/35R18 common | 25.58" | +1.96% | +50 mm | 61.2 mph | compare → |
| 265/35R18 common | 25.30" | +0.86% | +40 mm | 60.5 mph | compare → |
| 215/45R18 common | 25.62" | +2.12% | -10 mm | 61.3 mph | compare → |
| 245/35R18 common | 24.75" | -1.33% | +20 mm | 59.2 mph | compare → |
| 215/40R18 | 24.77" | -1.26% | -10 mm | 59.2 mph | compare → |
| 285/35R18 | 25.85" | +3.06% | +60 mm | 61.8 mph | compare → |
| 295/30R18 | 24.97" | -0.47% | +70 mm | 59.7 mph | compare → |
| 315/30R18 | 25.44" | +1.41% | +90 mm | 60.8 mph | compare → |
| 285/30R18 | 24.73" | -1.41% | +60 mm | 59.2 mph | compare → |
| 295/35R18 | 26.13" | +4.16% | +70 mm | 62.5 mph | compare → |
| 205/40R18 | 24.46" | -2.51% | -20 mm | 58.5 mph | compare → |
| 335/30R18 | 25.91" | +3.30% | +110 mm | 62.0 mph | compare → |
| 225/35R18 | 24.20" | -3.53% | 0 mm | 57.9 mph | calculate → |
| 215/35R18 | 23.93" | -4.63% | -10 mm | 57.2 mph | calculate → |
| 235/35R18 | 24.48" | -2.43% | +10 mm | 58.5 mph | calculate → |
| 305/30R18 | 25.20" | +0.47% | +80 mm | 60.3 mph | calculate → |
| 155/60R18 | 25.32" | +0.94% | -70 mm | 60.6 mph | calculate → |
| 145/70R18 | 25.99" | +3.61% | -80 mm | 62.2 mph | calculate → |
| 26x12.00R18 | 26.00" | +3.64% | +80 mm | 62.2 mph | calculate → |
| 26x6.00R18 | 26.00" | +3.64% | -73 mm | 62.2 mph | calculate → |
| 26x8.00R18 | 26.00" | +3.64% | -22 mm | 62.2 mph | calculate → |
| 205/45R18 | 25.26" | +0.71% | -20 mm | 60.4 mph | calculate → |
| 345/30R18 | 26.15" | +4.24% | +120 mm | 62.5 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 | |
|---|---|---|---|---|---|
| 225/45R17 common | 24.97" | -0.46% | 0 mm | 59.7 mph | compare → |
| 205/50R17 common | 25.07" | -0.06% | -20 mm | 60.0 mph | compare → |
| 235/45R17 common | 25.33" | +0.96% | +10 mm | 60.6 mph | compare → |
| 255/40R17 common | 25.03" | -0.22% | +30 mm | 59.9 mph | compare → |
| 225/35R19 | 25.20" | +0.46% | 0 mm | 60.3 mph | compare → |
| 255/30R19 | 25.02" | -0.25% | +30 mm | 59.8 mph | compare → |
| 265/30R19 | 25.26" | +0.69% | +40 mm | 60.4 mph | compare → |
| 295/35R17 | 25.13" | +0.17% | +70 mm | 60.1 mph | calculate → |
| 315/25R19 | 25.20" | +0.46% | +90 mm | 60.3 mph | calculate → |
| 145/70R17 | 24.99" | -0.38% | -80 mm | 59.8 mph | calculate → |
| 215/35R19 | 24.93" | -0.64% | -10 mm | 59.6 mph | calculate → |
Try another size against 225/40R18
Questions
What size is 225/40R18 in inches?
225/40R18 is about 25.1" tall and 8.9" wide on a 18-inch rim — roughly a 25x9.00R18 in inch sizing.
What does 225/40R18 mean?
225 mm section width, sidewall 40% of the width (3.54"), radial construction, 18-inch rim.
What tire sizes are equivalent to 225/40R18?
On the same 18" rim, within 3% of the diameter: 255/35R18 (-0.24%), 305/30R18 (+0.47%), 295/30R18 (-0.47%), 205/45R18 (+0.71%), 265/35R18 (+0.86%), 155/60R18 (+0.94%).
How many revolutions per mile does a 225/40R18 tire make?
About 804 revolutions per mile (circumference 78.8").
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.