235/40R18 tire size
235/40R18 is a metric size: 25.4" tall, 9.3" wide, on a 18" rim — about a 25.5x9.50R18. The sidewall is 3.7" and the tire turns 794 times per mile.
235/40R18 specs
| Overall diameter (height) | 25.40" · 645 mm |
|---|---|
| Section width | 9.25" · 235 mm |
| Sidewall height | 3.70" · 94 mm (40% of width) |
| Rim diameter | 18" |
| Circumference | 79.80" · 2.027 m |
| Revolutions per mile | 794 (493 per km) |
| Inch (flotation) equivalent | 25.5x9.50R18 |
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" | +1.24% | +10 mm | 60.7 mph | compare → |
| 225/45R18 common | 25.97" | +2.25% | -10 mm | 61.3 mph | compare → |
| 225/40R18 common | 25.09" | -1.24% | -10 mm | 59.3 mph | compare → |
| 235/45R18 common | 26.33" | +3.64% | 0 mm | 62.2 mph | compare → |
| 255/35R18 common | 25.03" | -1.47% | +20 mm | 59.1 mph | compare → |
| 255/40R18 common | 26.03" | +2.48% | +20 mm | 61.5 mph | compare → |
| 275/35R18 common | 25.58" | +0.70% | +40 mm | 60.4 mph | compare → |
| 265/35R18 common | 25.30" | -0.39% | +30 mm | 59.8 mph | compare → |
| 275/40R18 common | 26.66" | +4.96% | +40 mm | 63.0 mph | compare → |
| 215/45R18 common | 25.62" | +0.85% | -20 mm | 60.5 mph | compare → |
| 245/35R18 common | 24.75" | -2.56% | +10 mm | 58.5 mph | compare → |
| 215/40R18 | 24.77" | -2.48% | -20 mm | 58.5 mph | compare → |
| 285/35R18 | 25.85" | +1.78% | +50 mm | 61.1 mph | compare → |
| 265/40R18 | 26.35" | +3.72% | +30 mm | 62.2 mph | compare → |
| 295/30R18 | 24.97" | -1.70% | +60 mm | 59.0 mph | compare → |
| 315/30R18 | 25.44" | +0.15% | +80 mm | 60.1 mph | compare → |
| 285/30R18 | 24.73" | -2.63% | +50 mm | 58.4 mph | compare → |
| 295/35R18 | 26.13" | +2.87% | +60 mm | 61.7 mph | compare → |
| 205/40R18 | 24.46" | -3.72% | -30 mm | 57.8 mph | compare → |
| 335/30R18 | 25.91" | +2.01% | +100 mm | 61.2 mph | compare → |
| 215/50R18 | 26.46" | +4.18% | -20 mm | 62.5 mph | compare → |
| 225/35R18 | 24.20" | -4.73% | -10 mm | 57.2 mph | calculate → |
| 305/35R18 | 26.41" | +3.95% | +70 mm | 62.4 mph | calculate → |
| 235/35R18 | 24.48" | -3.64% | 0 mm | 57.8 mph | calculate → |
| 155/60R18 | 25.32" | -0.31% | -80 mm | 59.8 mph | calculate → |
| 305/30R18 | 25.20" | -0.77% | +70 mm | 59.5 mph | calculate → |
| 145/70R18 | 25.99" | +2.32% | -90 mm | 61.4 mph | calculate → |
| 26x12.00R18 | 26.00" | +2.36% | +70 mm | 61.4 mph | calculate → |
| 26x6.00R18 | 26.00" | +2.36% | -83 mm | 61.4 mph | calculate → |
| 26x8.00R18 | 26.00" | +2.36% | -32 mm | 61.4 mph | calculate → |
| 155/70R18 | 26.54" | +4.49% | -80 mm | 62.7 mph | calculate → |
| 205/45R18 | 25.26" | -0.54% | -30 mm | 59.7 mph | calculate → |
| 345/30R18 | 26.15" | +2.94% | +110 mm | 61.8 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 | |
|---|---|---|---|---|---|
| 215/50R17 common | 25.46" | +0.25% | -20 mm | 60.1 mph | compare → |
| 235/45R17 common | 25.33" | -0.29% | 0 mm | 59.8 mph | compare → |
| 235/35R19 common | 25.48" | +0.29% | 0 mm | 60.2 mph | compare → |
| 225/35R19 | 25.20" | -0.79% | -10 mm | 59.5 mph | compare → |
| 275/30R19 | 25.50" | +0.37% | +40 mm | 60.2 mph | compare → |
| 265/30R19 | 25.26" | -0.56% | +30 mm | 59.7 mph | compare → |
| 265/40R17 | 25.35" | -0.22% | +30 mm | 59.9 mph | calculate → |
| 155/70R17 | 25.54" | +0.56% | -80 mm | 60.3 mph | calculate → |
| 315/25R19 | 25.20" | -0.79% | +80 mm | 59.5 mph | calculate → |
Try another size against 235/40R18
Questions
What size is 235/40R18 in inches?
235/40R18 is about 25.4" tall and 9.3" wide on a 18-inch rim — roughly a 25.5x9.50R18 in inch sizing.
What does 235/40R18 mean?
235 mm section width, sidewall 40% of the width (3.70"), radial construction, 18-inch rim.
What tire sizes are equivalent to 235/40R18?
On the same 18" rim, within 3% of the diameter: 315/30R18 (+0.15%), 155/60R18 (-0.31%), 265/35R18 (-0.39%), 205/45R18 (-0.54%), 275/35R18 (+0.70%), 305/30R18 (-0.77%).
How many revolutions per mile does a 235/40R18 tire make?
About 794 revolutions per mile (circumference 79.8").
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.