tireheight.com

255/30R21 in inches

A 255/30R21 tire is 27.0″ tall and 10.0″ wide, and fits a 21″ wheel. In inches it is written 27.0×10.0R21.

Diameter27.02″
Width10.04″
Sidewall3.01″
255/30R21 drawn to scale: 27.02 inch diameter, 3.01 inch sidewall, 21 inch wheel, 10.04 inch tread width21″ wheel3.01″27.02″ overall10.04″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 255/30R21 tires really are

Heights published by Michelin for the one tire in this size. Their published revolutions per mile work out to 26.2″ under load (below).

The one tire listed, the Michelin Pilot Sport 4 S, measures 27.10″: 0.08″ taller than the size code's 27.02″.

Height under load26.2″

Published revs per mile (769) mean the tire rolls like a 26.2″ tire on the vehicle. Use this for speedometer calibration.

1 tire in 255/30R21

Sort by the spec you care about.

LoadRevs/miSource
Michelin Pilot Sport 4 SPerformanceXL · 93(Y)27.1025.59.51,433769Spec page

Is 255/30R21 a 27-inch tire?

≈27″

Yes. The size code works out to 27.02″, and the 1 tire here publishes 27.10″, 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 255/30R21Difference
275/25R2126.41-0.61″-2.3%
245/30R2126.79-0.24″-0.9%
295/25R2126.81-0.22″-0.8%
305/25R2127.00-0.02″-0.1%
255/35R2027.03+0.00″+0.0%
265/30R2127.26+0.24″+0.9%
325/25R2127.40+0.37″+1.4%
275/30R2127.50+0.47″+1.7%
285/30R2127.73+0.71″+2.6%
245/35R2127.75+0.73″+2.7%

How to read 255/30R21

How to read any tire size

255/30R21 93Y as printed on the tire sidewall, with each part numbered255/30R21 93Y123456
How 255/30R21 93Y 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.
1255Section width

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

230Aspect ratio

A percentage, not a measurement: the sidewall is 30% as tall as the tire is wide, which is 76.5 mm or 3.01 inches.

3RConstruction

Radial construction.

421Wheel diameter

Mounts on a 21-inch wheel. Approved wheel widths run 8.5″ to 9.5″.

593Load index

Each tire carries up to 1,433 lb (650 kg) at its maximum pressure.

6YSpeed rating

Rated for up to 186 mph sustained.

XLExtra load

Printed after the size.

SpecificationInchesMetric
Overall diameter27.02686 mm
Section width10.04255 mm
Sidewall height3.0176.5 mm
Circumference84.92,156 mm
Revolutions per mile (calculated, unloaded)746.3464 per km
Revolutions per mile (published by manufacturers)769478 per km
Approved wheel width8.5–9.5216–241 mm

Speedometer error after switching to 255/30R21

Your actual speed– mph

Questions about 255/30R21

What is 255/30R21 in inches?

27.02 inches tall, 10.04 inches wide, on a 21-inch wheel. Written in inches, that is roughly 27.0×10.0R21.

What wheel width do I need for 255/30R21?

Manufacturers approve 8.5–9.5″ wide wheels for this size.

How many revolutions per mile does a 255/30R21 make?

Published figures run 769 revolutions per mile. The calculated figure is 746.3, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 255/30R21 than 305/25R21?

0.02 inches taller on paper (27.02″ vs 27.00″), which raises the axle about 0.01″. Your speedometer will read about 0.1% slow.