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38×15.50R18 in inches

A 38×15.50R18 tire is 38.0″ tall and 15.5″ wide, and fits a 18″ wheel.

Diameter38.00″
Width15.50″
Sidewall10.00″
38×15.50R18 drawn to scale: 38.00 inch diameter, 10.00 inch sidewall, 18 inch wheel, 15.50 inch tread width18″ wheel10.00″38.00″ overall15.50″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 38×15.50R18 tires really are

Heights published by Toyo for the one tire in this size. Their published revolutions per mile work out to 36.7″ under load (below).

The one tire listed, the Toyo Open Country M/T, measures 37.72″: 0.28″ shorter than the size code's 38.00″.

Height under load36.7″

Published revs per mile (550) mean the tire rolls like a 36.7″ tire on the vehicle. Use this for speedometer calibration.

1 tire in 38×15.50R18

Sort by the spec you care about.

LoadRevs/miSource
Toyo Open Country M/TMud-terrainLT D · 128Q37.72103.121.03,970550Spec page

Is a 38×15.50R18 really 38 inches tall?

37.7″

Shorter. The name says 38″, and the 1 tire here publishes 37.72″.

All 38-inch tire sizes, on every wheel size.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

SizeDiameter ″vs 38×15.50R18Difference
37×12.50R1837.00-1.00″-2.6%
37×13.50R1837.00-1.00″-2.6%
37×12.50R1737.00-1.00″-2.6%
37×13.50R1737.00-1.00″-2.6%
38×11.50R1838.000.00″0.0%
38×13.50R1838.000.00″0.0%
38×11.50R1738.000.00″0.0%
38×12.50R1738.000.00″0.0%
39×13.50R1739.00+1.00″+2.6%
40×13.50R1840.00+2.00″+5.3%

How to read 38×15.50R18

How to read any tire size

38X15.50R18LT 128Q as printed on the tire sidewall, with each part numbered38X15.50R18LT 128Q1234567
How 38X15.50R18LT 128Q 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.
138Overall diameter

38 inches tall, measured on the approved wheel. Flotation sizes give every number in inches.

215.50Section width

15.50 inches across the widest point, or 394 mm.

3RConstruction

Radial construction.

418Wheel diameter

Mounts on a 18-inch wheel. Approved wheel widths run 11.0″ to 13.0″.

5LTLight truck

Marks a light truck (LT) tire.

6128Load index

Each tire carries up to 3,970 lb (1,800 kg) at its maximum pressure.

7QSpeed rating

Rated for up to 99 mph sustained.

DLoad range

Printed separately as "LOAD RANGE D": a 8-ply rating, inflated up to 65 psi (standard load-range table). The load range D tires here carry up to 3,970 lb each, as published.

SpecificationInchesMetric
Overall diameter38.00965 mm
Section width15.50394 mm
Sidewall height10.00254.0 mm
Circumference119.43,032 mm
Revolutions per mile (calculated, unloaded)530.7330 per km
Revolutions per mile (published by manufacturers)550342 per km
Approved wheel width11.0–13.0279–330 mm

Speedometer error after switching to 38×15.50R18

Your actual speed– mph

Questions about 38×15.50R18

What is 38×15.50R18 in inches?

38.00 inches tall, 15.50 inches wide, on a 18-inch wheel. Manufacturers publish 37.72 inches for the 1 tires listed here.

What wheel width do I need for 38×15.50R18?

Manufacturers approve 11.0–13.0″ wide wheels for this size.

How many revolutions per mile does a 38×15.50R18 make?

Published figures run 550 revolutions per mile. The calculated figure is 530.7, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 38×15.50R18 than 37×13.50R18?

1.00 inches taller on paper (38.00″ vs 37.00″), which raises the axle about 0.50″. Your speedometer will read about 2.7% slow.