235/40R18 tire size
A 235/40R18 tire is 25.4 inches tall and 9.3 inches wide. Here are its full dimensions, what the numbers mean, and the sizes you can swap it for.
- Overall diameter
- 25.40″ (645 mm)
- Section width
- 9.25″ (235 mm)
- Sidewall height
- 3.70″ (94 mm)
- Wheel diameter
- 18″
- Circumference
- 79.8″
- Revolutions per mile
- 794
What 235/40R18 means
- 235: the tire is 235 mm (9.3 in) wide from sidewall to sidewall.
- 40: the sidewall is 40% of the width, 94.0 mm (3.70 in) tall.
- R: radial construction, used by almost every modern tire.
- 18: it fits a 18-inch wheel.
Overall diameter = 18 + 2 × 3.70 = 25.40 inches.
Sizes equivalent to 235/40R18
These sizes are within 3% of the overall diameter, the usual limit for swapping without speedometer problems.
| Size | Diameter | Difference | Speedometer at 60 mph |
|---|---|---|---|
| 235/35R19 | 25.5″ | +0.3% | 60.2 mph actual |
| 225/30R20 | 25.3″ | -0.3% | 59.8 mph actual |
| 235/30R20 | 25.6″ | +0.6% | 60.4 mph actual |
| 225/35R19 | 25.2″ | -0.8% | 59.5 mph actual |
| 215/45R18 | 25.6″ | +0.9% | 60.5 mph actual |
| 225/40R18 | 25.1″ | -1.2% | 59.3 mph actual |
| 245/40R18 | 25.7″ | +1.2% | 60.7 mph actual |
| 215/30R20 | 25.1″ | -1.3% | 59.2 mph actual |
| 245/35R19 | 25.8″ | +1.4% | 60.8 mph actual |
| 215/40R19 | 25.8″ | +1.5% | 60.9 mph actual |
Going a size taller? 245/40R18 is 25.7″ tall, 1.2% more than 235/40R18. Compare any two sizes in the tire size calculator.
See every common size side by side in the tire size chart.
Questions
What is 235/40R18 in inches?
A 235/40R18 tire is about 25.4 inches tall (645 mm) and 9.3 inches wide, on a 18-inch wheel. In flotation sizing that's roughly 25.4x9.3R18.
How tall is a 235/40R18 tire?
The overall diameter is 25.40 inches: the 18-inch wheel plus two 3.70-inch sidewalls. Actual tires vary by a few tenths of an inch between brands and models.
Can I put 245/40R18 instead of 235/40R18?
245/40R18 is 0.31 inches taller (1.2%) and 10 mm wider. That's within the usual 3% limit, but check that your wheel width is approved for it and that it clears the suspension.
How many revolutions per mile does a 235/40R18 make?
About 794 revolutions per mile, from a circumference of 79.8 inches.
