235/40R18 tire size
A 235/40R18 tire stands 25.4 inches tall overall, on a 18-inch wheel, with a 94 mm sidewall and 235 mm of tread across. It turns roughly 794 times per mile.
- Overall diameter
- 25.40″
- 645.2 mm
- Sidewall height
- 94.0 mm
- 40% of 235 mm
- Circumference
- 79.8″
- 2,027 mm
- Revs per mile
- 794
- 493 per km
Reading the number
235 / 40 R 18 │ │ └─ rim diameter, 18 inches │ └──── aspect ratio, sidewall is 40% of width └──────── tread width, 235 mm sidewall = 235 × 0.40 = 94 mm diameter = (18 × 25.4) + (2 × 94) = 645.2 mm
Sizes that can replace 235/40R18
One rim step away, sorted by how close the rolling diameter stays.
Questions
›What does 235/40R18 mean?
235 is the tread width in millimetres. 40 is the aspect ratio, so the sidewall is 40% of 235 mm, or 94 mm. R means radial construction, and 18 is the wheel diameter in inches.
›How tall is a 235/40R18 tire?
25.4 inches, or 645.2 mm overall. That is the 18-inch rim plus a 94 mm sidewall at the top and another at the bottom.
›How many revolutions per mile does 235/40R18 do?
About 794 revolutions per mile, from a rolling circumference of 79.8 inches. Speedometers and odometers are calibrated against this figure, which is why changing size shifts both.
›What tires can replace 235/40R18?
Sizes within 3% of its rolling diameter and one rim step away, such as 225/40R18, 245/40R18, 225/45R17. Each is compared in full below.
Comparing against a size not listed? Open the calculator.