225/40R18 tire size
A 225/40R18 tire is 25.1 inches tall and 8.9 inches wide. Here are its full dimensions, what the numbers mean, and the sizes you can swap it for.
- Overall diameter
- 25.09″ (637 mm)
- Section width
- 8.86″ (225 mm)
- Sidewall height
- 3.54″ (90 mm)
- Wheel diameter
- 18″
- Circumference
- 78.8″
- Revolutions per mile
- 804
What 225/40R18 means
- 225: the tire is 225 mm (8.9 in) wide from sidewall to sidewall.
- 40: the sidewall is 40% of the width, 90.0 mm (3.54 in) tall.
- R: radial construction, used by almost every modern tire.
- 18: it fits a 18-inch wheel.
Overall diameter = 18 + 2 × 3.54 = 25.09 inches.
Sizes equivalent to 225/40R18
These sizes are within 3% of the overall diameter, the usual limit for swapping without speedometer problems.
| Size | Diameter | Difference | Speedometer at 60 mph |
|---|---|---|---|
| 215/30R20 | 25.1″ | -0.0% | 60.0 mph actual |
| 225/35R19 | 25.2″ | +0.5% | 60.3 mph actual |
| 215/35R19 | 24.9″ | -0.6% | 59.6 mph actual |
| 205/45R18 | 25.3″ | +0.7% | 60.4 mph actual |
| 225/30R20 | 25.3″ | +0.9% | 60.5 mph actual |
| 205/30R20 | 24.8″ | -1.0% | 59.4 mph actual |
| 245/30R19 | 24.8″ | -1.2% | 59.3 mph actual |
| 235/40R18 | 25.4″ | +1.3% | 60.8 mph actual |
| 215/40R18 | 24.8″ | -1.3% | 59.2 mph actual |
| 245/35R18 | 24.8″ | -1.3% | 59.2 mph actual |
Going a size taller? 235/40R18 is 25.4″ tall, 1.3% more than 225/40R18. Compare any two sizes in the tire size calculator.
See every common size side by side in the tire size chart.
Questions
What is 225/40R18 in inches?
A 225/40R18 tire is about 25.1 inches tall (637 mm) and 8.9 inches wide, on a 18-inch wheel. In flotation sizing that's roughly 25.1x8.9R18.
How tall is a 225/40R18 tire?
The overall diameter is 25.09 inches: the 18-inch wheel plus two 3.54-inch sidewalls. Actual tires vary by a few tenths of an inch between brands and models.
Can I put 235/40R18 instead of 225/40R18?
235/40R18 is 0.31 inches taller (1.3%) 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 225/40R18 make?
About 804 revolutions per mile, from a circumference of 78.8 inches.
