How tall is a 235/40R18 tire?

A 235/40R18 has a nominal overall diameter of 25.4 inches (645 mm), calculated as the 18-inch wheel plus two sidewalls. This is the unloaded figure — a fitted tire sits fractionally shorter under the weight of the vehicle.

What wheel size does a 235/40R18 tire fit?

A 235/40R18 fits a wheel of 18 inches in diameter. The wheel also has to be within the rim width range the manufacturer publishes for this size, which is printed in the tire's spec sheet.

What do the numbers in 235/40R18 mean?

235 is the section width in millimetres. 40 is the aspect ratio — the sidewall is 40% of the width, so 94 mm here. R marks the construction (radial). 18 is the wheel diameter in inches.

Size Dimensions & Specs

Tires Size 235/40R18

Dimensions, specs, and every size 235/40R18 tire currently in stock

Overall Height

25.4"

645 mm · calculated

Section Width

235 mm

9.25 inches

Sidewall Height

3.7"

94 mm · 40% profile

Wheel Diameter

18"

457.2 mm

235/40R18 Specifications

Read directly from the size code. Load index, speed rating, and rim width range vary by model.

Specification	Imperial	Metric
Section width	9.25 in	235 mm
Aspect ratio	40%	—
Sidewall height	3.7 in	94 mm
Overall diameter (calculated)	25.4 in	645 mm
Wheel / rim diameter	18 in	457.2 mm
Construction	Radial	—

What does 235/40R18 mean?

Reading the code on your sidewall

Section width

235 mm

The distance from sidewall to sidewall across the tire's widest point.

Aspect ratio

40% profile

The sidewall stands 40% of the section width, which is 94 mm on this size.

Construction (R)

Radial

The body plies run across the tire at right angles to the direction of travel.

Wheel diameter

18 in

Fits a wheel measuring 18 inches across.

235/40R18 Questions & Answers

Dimensions and fitment guidelines for size 235/40R18

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