315/35R21 in inches

A 315/35R21 tire is 29.7″ tall and 12.4″ wide, and fits a 21″ wheel. In inches it is written 29.7×12.4R21.

Diameter29.68″

Width12.40″

Sidewall4.34″

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

Manufacturer data

How tall 315/35R21 tires really are

Heights published by Michelin and Toyo for all 5 tires in this size. Their published revolutions per mile work out to 28.7–28.8″ under load (below).

Real 315/35R21 tires measure 29.60–29.70″, against 29.68″ from the size code. They run both taller and shorter than the size code.

Height under load28.7–28.8″

Published revs per mile (701–702) mean the tire rolls like a 28.7–28.8″ tire on the vehicle. Use this for speedometer calibration.

Weight spread34.4–40.6 lb

The lightest (Michelin Pilot Sport All-Season 4, XL) is 6.2 lb lighter per corner than the heaviest (Michelin Pilot Sport 4 SUV, XL).

5 tires in 315/35R21

Sort by the spec you care about.

	Load					Revs/mi	Source
Michelin Pilot Sport All-Season 4Performance	XL · 111Y	29.70	34.4	10.0	2,403	702	Spec page
Michelin Pilot Sport S 5Performance	XL · 111(Y)	29.70	34.9	9.0	2,403	702	Spec page
Toyo Proxes Sport 2Performance	XL · 111(Y)	29.60	36.2	9.2	2,403	701	Spec page
Michelin Pilot Sport 4 SUVPerformance	XL · 111Y	29.70	37.0	9.5	2,403	702	Spec page
Michelin Pilot Sport 4 SUVPerformance	XL · 111Y	29.70	40.6	9.0	2,403	702	Spec page

Is 315/35R21 a 30-inch tire?

≈30″

Yes. The size code works out to 29.68″, and the 5 tires here publish 29.60–29.70″, 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.

Size	Diameter ″	vs 315/35R21	Difference
295/35R21	29.13	-0.55″	-1.9%
345/30R21	29.15	-0.53″	-1.8%
235/45R21	29.33	-0.35″	-1.2%
265/40R21	29.35	-0.33″	-1.1%
305/35R21	29.41	-0.28″	-0.9%
275/40R21	29.66	-0.02″	-0.1%
245/45R21	29.68	0.00″	0.0%
285/40R21	29.98	+0.30″	+1.0%
255/45R21	30.04	+0.35″	+1.2%
235/50R21	30.25	+0.57″	+1.9%

How to read 315/35R21

How to read any tire size

How 315/35R21 111Y is printed on the sidewall. It's the most common code among the 5 tires here (3 of them); tires in this size come in other load and speed ratings too.

1315Section width

315 mm across the widest point, or 12.40 inches. Every 315 size

235Aspect ratio

A percentage, not a measurement: the sidewall is 35% as tall as the tire is wide, which is 110.2 mm or 4.34 inches.

3RConstruction

Radial construction.

421Wheel diameter

Mounts on a 21-inch wheel. Approved wheel widths run 10.5″ to 12.5″.

5111Load index

Each tire carries up to 2,403 lb (1,090 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	29.68	754 mm
Section width	12.40	315 mm
Sidewall height	4.34	110.2 mm
Circumference	93.2	2,368 mm
Revolutions per mile (calculated, unloaded)	679.5	422 per km
Revolutions per mile (published by manufacturers)	701–702	436 per km
Approved wheel width	10.5–12.5	267–318 mm

Speedometer error after switching to 315/35R21

Your actual speed– mph

Questions about 315/35R21

What is 315/35R21 in inches?

29.68 inches tall, 12.40 inches wide, on a 21-inch wheel. Written in inches, that is roughly 29.7×12.4R21.

How much does a 315/35R21 tire weigh?

Between 34.4 lb and 40.6 lb for the 5 tires listed here. The lightest is the Michelin Pilot Sport All-Season 4 (XL); the heaviest is the Michelin Pilot Sport 4 SUV (XL).

What wheel width do I need for 315/35R21?

Manufacturers approve 10.5–12.5″ wide wheels for this size.

How many revolutions per mile does a 315/35R21 make?

Published figures run 701–702 revolutions per mile. The calculated figure is 679.5, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 315/35R21 than 275/40R21?

0.02 inches taller on paper (29.68″ vs 29.66″), which raises the axle about 0.01″. Your speedometer will read about 0.1% slow.