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315/35R18 in inches

A 315/35R18 tire is 26.7″ tall and 12.4″ wide, and fits a 18″ wheel. In inches it is written 26.7×12.4R18.

Diameter26.68″
Width12.40″
Sidewall4.34″
315/35R18 drawn to scale: 26.68 inch diameter, 4.34 inch sidewall, 18 inch wheel, 12.40 inch tread width18″ wheel4.34″26.68″ overall12.40″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 315/35R18 tires really are

Heights published by Toyo for the one tire in this size. Their published revolutions per mile work out to 25.9″ under load (below).

The one tire listed, the Toyo Proxes TQ, measures 26.64″: 0.04″ shorter than the size code's 26.68″.

Height under load25.9″

Published revs per mile (780) mean the tire rolls like a 25.9″ tire on the vehicle. Use this for speedometer calibration.

1 tire in 315/35R18

Sort by the spec you care about.

LoadRevs/miSource
Toyo Proxes TQPerformanceLL26.6431.16.31,521780Spec page

Is 315/35R18 a 27-inch tire?

≈27″

Close. The size code works out to 26.68″, and the 1 tire here publishes 26.64″, so people call it a 27.

All 27-inch tire sizes, on every wheel size.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

SizeDiameter ″vs 315/35R18Difference
295/35R1826.13-0.55″-2.1%
235/45R1826.33-0.35″-1.3%
265/40R1826.35-0.33″-1.3%
305/35R1826.41-0.28″-1.0%
215/50R1826.46-0.22″-0.8%
275/40R1826.66-0.02″-0.1%
245/45R1826.680.00″0.0%
225/50R1826.86+0.18″+0.7%
285/40R1826.98+0.30″+1.1%
255/45R1827.04+0.35″+1.3%

How to read 315/35R18

How to read any tire size

P315/35R18 as printed on the tire sidewall, with each part numberedP315/35R1812345
How P315/35R18 is printed on the sidewall. It's the most common code among the 1 tire here; tires in this size come in other load and speed ratings too.
1PP-metric

Marks a P-metric (passenger) tire. Sizes with no letter are Euro-metric.

2315Section width

315 mm across the widest point, or 12.40 inches. Every 315 size

335Aspect ratio

A percentage, not a measurement: the sidewall is 35% as tall as the tire is wide, which is 110.2 mm or 4.34 inches.

4RConstruction

Radial construction.

518Wheel diameter

Mounts on a 18-inch wheel. Approved wheel widths run 10.5″ to 12.5″.

SpecificationInchesMetric
Overall diameter26.68678 mm
Section width12.40315 mm
Sidewall height4.34110.2 mm
Circumference83.82,129 mm
Revolutions per mile (calculated, unloaded)755.9470 per km
Revolutions per mile (published by manufacturers)780485 per km
Approved wheel width10.5–12.5267–318 mm

Speedometer error after switching to 315/35R18

Your actual speed– mph

Questions about 315/35R18

What is 315/35R18 in inches?

26.68 inches tall, 12.40 inches wide, on a 18-inch wheel. Written in inches, that is roughly 26.7×12.4R18.

What wheel width do I need for 315/35R18?

Manufacturers approve 10.5–12.5″ wide wheels for this size.

How many revolutions per mile does a 315/35R18 make?

Published figures run 780 revolutions per mile. The calculated figure is 755.9, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 315/35R18 than 275/40R18?

0.02 inches taller on paper (26.68″ vs 26.66″), which raises the axle about 0.01″. Your speedometer will read about 0.1% slow.