225/40R18 tire size
A 225/40R18 tire stands 25.09 inches tall overall, on a 18-inch wheel, with a 90 mm sidewall and 225 mm of tread across. It turns roughly 804 times per mile.
- Overall diameter
- 25.09″
- 637.2 mm
- Sidewall height
- 90.0 mm
- 40% of 225 mm
- Circumference
- 78.8″
- 2,002 mm
- Revs per mile
- 804
- 500 per km
Reading the number
225 / 40 R 18 │ │ └─ rim diameter, 18 inches │ └──── aspect ratio, sidewall is 40% of width └──────── tread width, 225 mm sidewall = 225 × 0.40 = 90 mm diameter = (18 × 25.4) + (2 × 90) = 637.2 mm
Sizes that can replace 225/40R18
One rim step away, sorted by how close the rolling diameter stays.
Questions
›What does 225/40R18 mean?
225 is the tread width in millimetres. 40 is the aspect ratio, so the sidewall is 40% of 225 mm, or 90 mm. R means radial construction, and 18 is the wheel diameter in inches.
›How tall is a 225/40R18 tire?
25.09 inches, or 637.2 mm overall. That is the 18-inch rim plus a 90 mm sidewall at the top and another at the bottom.
›How many revolutions per mile does 225/40R18 do?
About 804 revolutions per mile, from a rolling circumference of 78.8 inches. Speedometers and odometers are calibrated against this figure, which is why changing size shifts both.
›What tires can replace 225/40R18?
Sizes within 3% of its rolling diameter and one rim step away, such as 225/45R17, 235/40R18, 245/40R18. Each is compared in full below.
Comparing against a size not listed? Open the calculator.