325/30R21 in inches

A 325/30R21 tire is 28.7″ tall and 12.8″ wide, and fits a 21″ wheel. In inches it is written 28.7×12.8R21.

Diameter28.68″

Width12.80″

Sidewall3.84″

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

Manufacturer data

How tall 325/30R21 tires really are

Heights published by Michelin and Toyo for all 15 tires in this size. Their published revolutions per mile work out to 27.8–27.9″ under load (below).

Real 325/30R21 tires measure 28.70″, against 28.68″ from the size code. Every one runs taller than the size code.

Height under load27.8–27.9″

Published revs per mile (724–725) mean the tire rolls like a 27.8–27.9″ tire on the vehicle. Use this for speedometer calibration.

Weight spread31.5–40.6 lb

The lightest (Michelin Pilot Sport S 5, XL) is 9.1 lb lighter per corner than the heaviest (Toyo Observe G3-Ice, XL).

15 tires in 325/30R21

Sort by the spec you care about.

	Load					Revs/mi	Source
Michelin Pilot Sport S 5Performance	XL · 108(Y)	28.70	31.5	9.0	2,205	725	Spec page
Michelin Pilot Sport S 5Performance	XL · 108(Y)	28.70	31.5	9.0	2,205	725	Spec page
Michelin Pilot Sport Cup 2 ConnectPerformance	XL · 108(Y)	28.70	31.6	7.2	2,205	725	Spec page
Michelin Pilot Sport S 5Performance	XL · 108(Y)	28.70	32.3	9.0	2,205	725	Spec page
Michelin Pilot Sport Cup 2 RPerformance	XL · 108(Y)	28.70	32.6	5.5	2,205	725	Spec page
Michelin Pilot Sport 4 SPerformance	XL · 108(Y)	28.70	33.0	9.5	2,205	725	Spec page
Michelin Pilot Sport All-Season 4Performance	XL · 108V	28.70	33.1	9.5	2,205	725	Spec page
Michelin Pilot Super SportPerformance	XL · 108Y	28.70	33.2	10.0	2,205	725	Spec page
Michelin Pilot Sport 4 SPerformance	XL · 108(Y)	28.70	33.5	9.5	2,205	725	Spec page
Michelin Pilot Sport S 5Performance	XL · 108(Y)	28.70	33.5	9.0	2,205	725	Spec page
Michelin Pilot Sport Cup 2Performance	SL · 104(Y)	28.70	33.9	7.2	1,984	725	Spec page
Michelin Pilot Sport Cup 2Performance	XL · 108(Y)	28.70	34.0	7.2	2,205	725	Spec page
Michelin Pilot Sport 4Performance	XL · 108(Y)	28.70	34.1	9.5	2,205	725	Spec page
Toyo Proxes Sport 2Performance	XL · 108Y	28.70	35.7	9.2	2,205	724	Spec page
Toyo Observe G3-IceWinter	XL · 108T	28.70	40.6	12.0	2,205	724	Spec page

Is 325/30R21 a 29-inch tire?

≈29″

Yes. The size code works out to 28.68″, and the 15 tires here publish 28.70″, so people call it a 29.

All 29-inch tire sizes, on every wheel size.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

Size	Diameter ″	vs 325/30R21	Difference
265/35R21	28.30	-0.37″	-1.3%
315/30R21	28.44	-0.24″	-0.8%
275/35R21	28.58	-0.10″	-0.3%
245/40R21	28.72	+0.04″	+0.1%
285/35R21	28.85	+0.18″	+0.6%
335/30R21	28.91	+0.24″	+0.8%
225/45R21	28.97	+0.30″	+1.0%
255/40R21	29.03	+0.35″	+1.2%
295/35R21	29.13	+0.45″	+1.6%
345/30R21	29.15	+0.47″	+1.6%

How to read 325/30R21

How to read any tire size

How 325/30R21 108Y is printed on the sidewall. It's the most common code among the 15 tires here (10 of them); tires in this size come in other load and speed ratings too.

1325Section width

325 mm across the widest point, or 12.80 inches. Every 325 size

230Aspect ratio

A percentage, not a measurement: the sidewall is 30% as tall as the tire is wide, which is 97.5 mm or 3.84 inches.

3RConstruction

Radial construction.

421Wheel diameter

Mounts on a 21-inch wheel. Approved wheel widths run 11.0″ to 12.0″.

5108Load index

Each tire carries up to 2,205 lb (1,000 kg) at its maximum pressure.

6YSpeed rating

Rated for up to 186 mph sustained.

XLExtra load

Printed after the size. In this size the XL tires carry up to 2,205 lb each and the standard-load tires up to 1,984 lb, as published.

Specification	Inches	Metric
Overall diameter	28.68	728 mm
Section width	12.80	325 mm
Sidewall height	3.84	97.5 mm
Circumference	90.1	2,288 mm
Revolutions per mile (calculated, unloaded)	703.3	437 per km
Revolutions per mile (published by manufacturers)	724–725	450 per km
Approved wheel width	11.0–12.0	279–305 mm

Speedometer error after switching to 325/30R21

Your actual speed– mph

Questions about 325/30R21

What is 325/30R21 in inches?

28.68 inches tall, 12.80 inches wide, on a 21-inch wheel. Written in inches, that is roughly 28.7×12.8R21.

How much does a 325/30R21 tire weigh?

Between 31.5 lb and 40.6 lb for the 15 tires listed here. The lightest is the Michelin Pilot Sport S 5 (XL); the heaviest is the Toyo Observe G3-Ice (XL).

What wheel width do I need for 325/30R21?

Manufacturers approve 11.0–12.0″ wide wheels for this size.

How many revolutions per mile does a 325/30R21 make?

Published figures run 724–725 revolutions per mile. The calculated figure is 703.3, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 325/30R21 than 275/35R21?

0.10 inches taller on paper (28.68″ vs 28.58″), which raises the axle about 0.05″. Your speedometer will read about 0.3% slow.