235/40R18 tire size

A 235/40R18 tire is 235 mm wide with a sidewall 40% of its width (94.0 mm), fits a 18-inch rim and has an overall diameter of 645 mm (25.4 in).

DimensionMetricImperial
Section width235 mm9.25 in
Sidewall height94.0 mm3.70 in
Rim diameter457.2 mm18 in
Overall diameter645.2 mm25.40 in
Circumference2,027.0 mm79.80 in
Revolutions493 per km794 per mile

Reading the size 235/40R18

235Width in mm40Aspect ratio (sidewall % of width)RRadial construction18Rim diameter in inches

The load index and speed rating (for example 91V) follow the size on the sidewall. Replacement tires should match or exceed the original load index and speed rating.

Alternative sizes within 3% of 235/40R18

A replacement size should stay within about 3% of the original diameter so the speedometer, ABS and transmission stay accurate. Always check clearance, load index and the vehicle manufacturer's approved sizes.

SizeDiameterDifferenceSpeedo reads 100 → actual
215/50R17647 mm+0.2%100.2Compare
235/35R19647 mm+0.3%100.3Compare
235/45R17643 mm-0.3%99.7Compare
205/65R15648 mm+0.4%100.4Compare
215/55R16643 mm-0.4%99.6Compare
265/35R18643 mm-0.4%99.6Compare
225/35R19640 mm-0.8%99.2Compare
215/45R18651 mm+0.9%100.9

Compare 235/40R18 with any size →

Other 18-inch sizes

215/45R18215/55R18225/40R18225/45R18225/50R18225/55R18225/60R18235/45R18235/50R18235/55R18235/60R18235/65R18245/40R18245/45R18245/60R18255/55R18255/60R18255/65R18255/70R18265/35R18265/60R18265/65R18265/70R18275/65R18275/70R18