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255/50R21 in inches

A 255/50R21 tire is 31.0″ tall and 10.0″ wide, and fits a 21″ wheel. In inches it is written 31.0×10.0R21.

Diameter31.04″
Width10.04″
Sidewall5.02″
255/50R21 drawn to scale: 31.04 inch diameter, 5.02 inch sidewall, 21 inch wheel, 10.04 inch tread width21″ wheel5.02″31.04″ overall10.04″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 255/50R21 tires really are

Heights published by Michelin for all 4 tires in this size. Their published revolutions per mile work out to 30.1″ under load (below).

Real 255/50R21 tires measure 31.00–31.10″, against 31.04″ from the size code. Most run taller than the size code (3 of 4).

Height under load30.1″

Published revs per mile (670) mean the tire rolls like a 30.1″ tire on the vehicle. Use this for speedometer calibration.

Weight spread34.3–35.3 lb

The lightest (Michelin Primacy All Season, XL) is 1.0 lb lighter per corner than the heaviest (Michelin X-Ice Snow, XL).

4 tires in 255/50R21

Sort by the spec you care about.

LoadRevs/miSource
Michelin Primacy All SeasonTouringXL · 109H31.0034.39.52,271670Spec page
Michelin Primacy Tour A/STouringXL · 109H31.1034.49.02,271670Spec page
Michelin Primacy Tour A/STouringXL · 109H31.1034.49.02,271670Spec page
Michelin X-Ice SnowWinterXL · 109H31.0635.310.52,271670Spec page

Is 255/50R21 a 31-inch tire?

≈31″

Yes. The size code works out to 31.04″, and the 4 tires here publish 31.00–31.10″, so people call it a 31.

All 31-inch tire sizes, on every wheel size.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

SizeDiameter ″vs 255/50R21Difference
235/50R2130.25-0.79″-2.5%
295/40R2130.29-0.75″-2.4%
265/45R2130.39-0.65″-2.1%
305/40R2130.61-0.43″-1.4%
275/45R2130.74-0.30″-1.0%
315/40R2130.92-0.12″-0.4%
255/45R2231.04-0.00″-0.0%
255/55R2031.04+0.00″+0.0%
285/45R2131.10+0.06″+0.2%
275/50R2131.83+0.79″+2.5%

How to read 255/50R21

How to read any tire size

255/50R21 109H as printed on the tire sidewall, with each part numbered255/50R21 109H123456
How 255/50R21 109H is printed on the sidewall. It's the most common code among the 4 tires here; tires in this size come in other load and speed ratings too.
1255Section width

255 mm across the widest point, or 10.04 inches. Every 255 size

250Aspect ratio

A percentage, not a measurement: the sidewall is 50% as tall as the tire is wide, which is 127.5 mm or 5.02 inches.

3RConstruction

Radial construction.

421Wheel diameter

Mounts on a 21-inch wheel. Approved wheel widths run 7.0″ to 9.0″.

5109Load index

Each tire carries up to 2,271 lb (1,030 kg) at its maximum pressure.

6HSpeed rating

Rated for up to 130 mph sustained.

XLExtra load

Printed after the size.

SpecificationInchesMetric
Overall diameter31.04788 mm
Section width10.04255 mm
Sidewall height5.02127.5 mm
Circumference97.52,477 mm
Revolutions per mile (calculated, unloaded)649.8404 per km
Revolutions per mile (published by manufacturers)670416 per km
Approved wheel width7.0–9.0178–229 mm

Speedometer error after switching to 255/50R21

Your actual speed– mph

Questions about 255/50R21

What is 255/50R21 in inches?

31.04 inches tall, 10.04 inches wide, on a 21-inch wheel. Written in inches, that is roughly 31.0×10.0R21.

How much does a 255/50R21 tire weigh?

Between 34.3 lb and 35.3 lb for the 4 tires listed here. The lightest is the Michelin Primacy All Season (XL); the heaviest is the Michelin X-Ice Snow (XL).

What wheel width do I need for 255/50R21?

Manufacturers approve 7.0–9.0″ wide wheels for this size.

How many revolutions per mile does a 255/50R21 make?

Published figures run 670 revolutions per mile. The calculated figure is 649.8, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 255/50R21 than 315/40R21?

0.12 inches taller on paper (31.04″ vs 30.92″), which raises the axle about 0.06″. Your speedometer will read about 0.4% slow.