245/40R18 tire size

A 245/40R18 tire is 25.7 inches (653 mm) tall and 9.6 inches (245 mm) wide, and fits a 18-inch wheel. In inch sizing it is about a 25.7x9.6R18.

Overall diameter25.72in653 mm

Drawn to scale from the nominal size.

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Size	Diameter	Difference	Width	Sidewall	Wheel
225/55R16	25.7″	+0.1%	8.9″	4.9″	16″
205/60R16	25.7″	−0.1%	8.1″	4.8″	16″
245/35R19	25.8″	+0.1%	9.6″	3.4″	19″
245/45R17	25.7″	−0.1%	9.6″	4.3″	17″
225/60R15	25.6″	−0.3%	8.9″	5.3″	15″
215/45R18	25.6″	−0.4%	8.5″	3.8″	18″
275/35R18	25.6″	−0.5%	10.8″	3.8″	18″
225/50R17	25.9″	+0.6%	8.9″	4.4″	17″
205/55R17	25.9″	+0.6%	8.1″	4.4″	17″
195/75R14	25.5″	−0.8%	7.7″	5.8″	14″
205/65R15	25.5″	−0.9%	8.1″	5.2″	15″
235/35R19	25.5″	−0.9%	9.3″	3.2″	19″

Within 3% of the original diameter is the range most tire shops treat as a direct swap. Check load index and clearance too.

245: Section width: 245 mm (9.6 in) from sidewall to sidewall.
40: Aspect ratio: the sidewall is 40% as tall as the tire is wide, 98 mm (3.9 in).
R: Radial construction, used by almost every modern tire.
18: Fits a 18-inch wheel.

245/40R18 is about 25.7 inches tall and 9.6 inches wide, on a 18-inch wheel, roughly a 25.7x9.6R18 in inch sizing.

Yes. At 25.7 inches it is sold and fitted as a 26-inch tire.

225/55R16, 205/60R16, 245/35R19 are the closest common sizes, all within 0.1% of its diameter, so the speedometer stays close to accurate.

275/40R18 is 3.7% taller, so at an indicated 60 mph you would really be doing 62.2 mph. Compare 245/40R18 and 275/40R18.

About 784 per mile (487 per km), from a 80.8-inch circumference.