355/25R21 in inches

A 355/25R21 tire is 28.0″ tall and 14.0″ wide, and fits a 21″ wheel. In inches it is written 28.0×14.0R21.

Diameter27.99″

Width13.98″

Sidewall3.49″

Drawn to scale. Nominal dimensions calculated from the size code.

Manufacturer data

How tall 355/25R21 tires really are

Heights published by Michelin for the one tire in this size. Their published revolutions per mile work out to 27.1″ under load (below).

The one tire listed, the Michelin Pilot Sport 4 S, measures 28.00″: 0.01″ taller than the size code's 27.99″.

Height under load27.1″

Published revs per mile (743) mean the tire rolls like a 27.1″ tire on the vehicle. Use this for speedometer calibration.

1 tire in 355/25R21

Sort by the spec you care about.

	Load					Revs/mi	Source
Michelin Pilot Sport 4 SPerformance	XL · 107(Y)	28.00	34.5	9.5	2,149	743	Spec page

Is 355/25R21 a 28-inch tire?

≈28″

Yes. The size code works out to 27.99″, and the 1 tire here publishes 28.00″, so people call it a 28.

All 28-inch tire sizes, on every wheel size.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

Size	Diameter ″	vs 355/25R21	Difference
325/25R21	27.40	-0.59″	-2.1%
275/30R21	27.50	-0.49″	-1.8%
285/30R21	27.73	-0.26″	-0.9%
245/35R21	27.75	-0.24″	-0.8%
345/25R21	27.79	-0.20″	-0.7%
295/30R21	27.97	-0.02″	-0.1%
255/35R21	28.03	+0.04″	+0.1%
305/30R21	28.20	+0.22″	+0.8%
265/35R21	28.30	+0.31″	+1.1%
315/30R21	28.44	+0.45″	+1.6%

How to read 355/25R21

How to read any tire size

How 355/25R21 107Y 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.

1355Section width

355 mm across the widest point, or 13.98 inches. Every 355 size

225Aspect ratio

A percentage, not a measurement: the sidewall is 25% as tall as the tire is wide, which is 88.8 mm or 3.49 inches.

3RConstruction

Radial construction.

421Wheel diameter

Mounts on a 21-inch wheel. Approved wheel widths run 12.5″ to 13.5″.

5107Load index

Each tire carries up to 2,149 lb (975 kg) at its maximum pressure.

6YSpeed rating

Rated for up to 186 mph sustained.

XLExtra load

Printed after the size.

Specification	Inches	Metric
Overall diameter	27.99	711 mm
Section width	13.98	355 mm
Sidewall height	3.49	88.8 mm
Circumference	87.9	2,233 mm
Revolutions per mile (calculated, unloaded)	720.6	448 per km
Revolutions per mile (published by manufacturers)	743	462 per km
Approved wheel width	12.5–13.5	318–343 mm

Speedometer error after switching to 355/25R21

Your actual speed– mph

Questions about 355/25R21

What is 355/25R21 in inches?

27.99 inches tall, 13.98 inches wide, on a 21-inch wheel. Written in inches, that is roughly 28.0×14.0R21.

What wheel width do I need for 355/25R21?

Manufacturers approve 12.5–13.5″ wide wheels for this size.

How many revolutions per mile does a 355/25R21 make?

Published figures run 743 revolutions per mile. The calculated figure is 720.6, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 355/25R21 than 295/30R21?

0.02 inches taller on paper (27.99″ vs 27.97″), which raises the axle about 0.01″. Your speedometer will read about 0.1% slow.