245/40R18 tire size
A 245/40R18 tire is 25.7 inches tall and 9.6 inches wide. Here are its full dimensions, what the numbers mean, and the sizes you can swap it for.
- Overall diameter
- 25.72″ (653 mm)
- Section width
- 9.65″ (245 mm)
- Sidewall height
- 3.86″ (98 mm)
- Wheel diameter
- 18″
- Circumference
- 80.8″
- Revolutions per mile
- 784
What 245/40R18 means
- 245: the tire is 245 mm (9.6 in) wide from sidewall to sidewall.
- 40: the sidewall is 40% of the width, 98.0 mm (3.86 in) tall.
- R: radial construction, used by almost every modern tire.
- 18: it fits a 18-inch wheel.
Overall diameter = 18 + 2 × 3.86 = 25.72 inches.
Sizes equivalent to 245/40R18
These sizes are within 3% of the overall diameter, the usual limit for swapping without speedometer problems.
| Size | Diameter | Difference | Speedometer at 60 mph |
|---|---|---|---|
| 245/35R19 | 25.8″ | +0.1% | 60.1 mph actual |
| 245/30R20 | 25.8″ | +0.3% | 60.2 mph actual |
| 235/30R20 | 25.6″ | -0.6% | 59.6 mph actual |
| 235/35R19 | 25.5″ | -0.9% | 59.4 mph actual |
| 225/45R18 | 26.0″ | +1.0% | 60.6 mph actual |
| 255/30R20 | 26.0″ | +1.2% | 60.7 mph actual |
| 255/35R19 | 26.0″ | +1.2% | 60.7 mph actual |
| 235/40R18 | 25.4″ | -1.2% | 59.3 mph actual |
| 255/40R18 | 26.0″ | +1.2% | 60.7 mph actual |
| 225/40R19 | 26.1″ | +1.4% | 60.9 mph actual |
Going a size taller? 225/45R18 is 26.0″ tall, 1.0% more than 245/40R18. Compare any two sizes in the tire size calculator.
See every common size side by side in the tire size chart.
Questions
What is 245/40R18 in inches?
A 245/40R18 tire is about 25.7 inches tall (653 mm) and 9.6 inches wide, on a 18-inch wheel. In flotation sizing that's roughly 25.7x9.6R18.
How tall is a 245/40R18 tire?
The overall diameter is 25.72 inches: the 18-inch wheel plus two 3.86-inch sidewalls. Actual tires vary by a few tenths of an inch between brands and models.
How many revolutions per mile does a 245/40R18 make?
About 784 revolutions per mile, from a circumference of 80.8 inches.
