tireheight.com

255/45R21 in inches

A 255/45R21 tire is 30.0″ tall and 10.0″ wide, and fits a 21″ wheel. In inches it is written 30.0×10.0R21.

Diameter30.04″
Width10.04″
Sidewall4.52″
255/45R21 drawn to scale: 30.04 inch diameter, 4.52 inch sidewall, 21 inch wheel, 10.04 inch tread width21″ wheel4.52″30.04″ overall10.04″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 255/45R21 tires really are

Heights published by Michelin for all 5 tires in this size. Their published revolutions per mile work out to 29.1″ under load (below).

Real 255/45R21 tires measure 30.00–30.04″, against 30.04″ from the size code. They run both taller and shorter than the size code.

Height under load29.1″

Published revs per mile (692) mean the tire rolls like a 29.1″ tire on the vehicle. Use this for speedometer calibration.

Weight spread31.4–32.4 lb

The lightest (Michelin Pilot Sport EV, XL) is 1.0 lb lighter per corner than the heaviest (Michelin Pilot Alpin 5, XL).

5 tires in 255/45R21

Sort by the spec you care about.

LoadRevs/miSource
Michelin Pilot Sport EVPerformanceXL · 106Y30.0031.48.52,094692Spec page
Michelin Pilot Sport All-Season 4PerformanceXL · 106V30.0031.89.02,094692Spec page
Michelin X-Ice SnowWinterXL · 106H30.0432.110.52,094692Spec page
Michelin Pilot Alpin 5WinterXL · 106V30.0432.410.52,094692Spec page
Michelin Primacy All SeasonTouringXL · 106W30.0032.48.52,094692Spec page

Is 255/45R21 a 30-inch tire?

≈30″

Yes. The size code works out to 30.04″, and the 5 tires here publish 30.00–30.04″, so people call it a 30.

All 30-inch tire sizes, on every wheel size.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

SizeDiameter ″vs 255/45R21Difference
265/40R2129.35-0.69″-2.3%
305/35R2129.41-0.63″-2.1%
275/40R2129.66-0.37″-1.2%
245/45R2129.68-0.35″-1.2%
315/35R2129.68-0.35″-1.2%
285/40R2129.98-0.06″-0.2%
235/50R2130.25+0.22″+0.7%
295/40R2130.29+0.26″+0.9%
265/45R2130.39+0.35″+1.2%
305/40R2130.61+0.57″+1.9%

How to read 255/45R21

How to read any tire size

255/45R21 106V as printed on the tire sidewall, with each part numbered255/45R21 106V123456
How 255/45R21 106V is printed on the sidewall. It's the most common code among the 5 tires here (2 of them); 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

245Aspect ratio

A percentage, not a measurement: the sidewall is 45% as tall as the tire is wide, which is 114.8 mm or 4.52 inches.

3RConstruction

Radial construction.

421Wheel diameter

Mounts on a 21-inch wheel. Approved wheel widths run 8.0″ to 9.5″.

5106Load index

Each tire carries up to 2,094 lb (950 kg) at its maximum pressure.

6VSpeed rating

Rated for up to 149 mph sustained.

XLExtra load

Printed after the size.

SpecificationInchesMetric
Overall diameter30.04763 mm
Section width10.04255 mm
Sidewall height4.52114.8 mm
Circumference94.42,397 mm
Revolutions per mile (calculated, unloaded)671.5417 per km
Revolutions per mile (published by manufacturers)692430 per km
Approved wheel width8.0–9.5203–241 mm

Speedometer error after switching to 255/45R21

Your actual speed– mph

Questions about 255/45R21

What is 255/45R21 in inches?

30.04 inches tall, 10.04 inches wide, on a 21-inch wheel. Written in inches, that is roughly 30.0×10.0R21.

How much does a 255/45R21 tire weigh?

Between 31.4 lb and 32.4 lb for the 5 tires listed here. The lightest is the Michelin Pilot Sport EV (XL); the heaviest is the Michelin Pilot Alpin 5 (XL).

What wheel width do I need for 255/45R21?

Manufacturers approve 8.0–9.5″ wide wheels for this size.

How many revolutions per mile does a 255/45R21 make?

Published figures run 692 revolutions per mile. The calculated figure is 671.5, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 255/45R21 than 285/40R21?

0.06 inches taller on paper (30.04″ vs 29.98″), which raises the axle about 0.03″. Your speedometer will read about 0.2% slow.