305/30R20 in inches

A 305/30R20 tire is 27.2″ tall and 12.0″ wide, and fits a 20″ wheel. In inches it is written 27.2×12.0R20.

Diameter27.20″

Width12.01″

Sidewall3.60″

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

Manufacturer data

How tall 305/30R20 tires really are

Heights published by General, Michelin and Toyo for all 23 tires in this size. Their published revolutions per mile work out to 26.4″ under load (below).

Real 305/30R20 tires measure 27.20–27.40″, against 27.20″ from the size code. They run both taller and shorter than the size code.

Michelin Pilot Sport All-Season 4 · 227.20–27.40″ +0.20″
Michelin Pilot Alpin PA427.24″ +0.04″
General G-MAX RS27.20″ −0.00″
Michelin Pilot Sport 4 S · 527.20″ −0.00″
Michelin Pilot Sport Cup 2 · 527.20″ −0.00″
Michelin Pilot Sport Cup 2 Connect27.20″ −0.00″
Michelin Pilot Sport Cup 2 R · 427.20″ −0.00″
Michelin Pilot Sport S 527.20″ −0.00″
Michelin Pilot Super Sport · 227.20″ −0.00″
Toyo Proxes Sport 227.20″ −0.00″

Each bar runs from the size code's 27.20″ (the orange line) to the model's published height. The track spans 1.0″. Where a model comes in several load ranges, the darker part shows its range of heights; the number after the name is how many versions it comes in.

Height under load26.4″

Published revs per mile (763–764) mean the tire rolls like a 26.4″ tire on the vehicle. Use this for speedometer calibration.

Weight spread27.8–35.5 lb

The lightest (General G-MAX RS, XL) is 7.7 lb lighter per corner than the heaviest (Michelin Pilot Sport S 5, XL).

23 tires in 305/30R20

Sort by the spec you care about.

	Load					Revs/mi	Source
General G-MAX RSPerformance	XL · 103Y	27.20	27.8	10.0	1,929	764	Spec page
Michelin Pilot Sport Cup 2Performance	XL · 103(Y)	27.20	29.1	5.5	1,929	764	Spec page
Michelin Pilot Sport Cup 2 RPerformance	XL · 103(Y)	27.20	29.2	5.5	1,929	764	Spec page
Michelin Pilot Sport Cup 2 RPerformance	XL · 103(Y)	27.20	29.3	5.5	1,929	764	Spec page
Michelin Pilot Sport Cup 2 RPerformance	XL · 103(Y)	27.20	29.5	5.5	1,929	764	Spec page
Michelin Pilot Sport Cup 2 RPerformance	SL · 99(Y)	27.20	29.6	5.5	1,709	764	Spec page
Michelin Pilot Sport Cup 2Performance	XL · 103(Y)	27.20	29.8	7.2	1,929	764	Spec page
Michelin Pilot Sport All-Season 4Performance	XL · 103Y	27.20	29.9	10.0	1,929	764	Spec page
Michelin Pilot Sport Cup 2Performance	XL · 103(Y)	27.20	30.3	7.2	1,929	764	Spec page
Michelin Pilot Sport 4 SPerformance	XL · 103(Y)	27.20	30.5	9.0	1,929	764	Spec page
Michelin Pilot Sport 4 SPerformance	XL · 103(Y)	27.20	30.5	8.5	1,929	764	Spec page
Michelin Pilot Sport 4 SPerformance	XL · 103(Y)	27.20	30.6	9.5	1,929	764	Spec page
Michelin Pilot Sport Cup 2Performance	XL · 103(Y)	27.20	30.6	7.2	1,929	764	Spec page
Michelin Pilot Sport Cup 2 ConnectPerformance	XL · 103(Y)	27.20	30.7	7.2	1,929	764	Spec page
Michelin Pilot Alpin PA4Winter	XL · 103W	27.24	30.8	10.5	1,929	764	Spec page
Michelin Pilot Sport Cup 2Performance	XL · 103(Y)	27.20	30.8	7.2	1,929	764	Spec page
Michelin Pilot Super SportPerformance	XL · 103(Y)	27.20	31.0	9.0	1,929	764	Spec page
Michelin Pilot Sport 4 SPerformance	XL · 103(Y)	27.20	31.1	9.0	1,929	764	Spec page
Michelin Pilot Super SportPerformance	XL · 103(Y)	27.20	31.3	10.0	1,929	764	Spec page
Toyo Proxes Sport 2Performance	XL · 103Y	27.20	32.6	9.2	1,929	763	Spec page
Michelin Pilot Sport 4 SPerformance	XL · 103(Y)	27.20	34.9	8.5	1,929	764	Spec page
Michelin Pilot Sport All-Season 4Performance	SL · 99(Y)	27.40	35.2	10.0	1,709	764	Spec page
Michelin Pilot Sport S 5Performance	XL · 103(Y)	27.20	35.5	8.5	1,929	764	Spec page

Is 305/30R20 a 27-inch tire?

≈27″

Yes. The size code works out to 27.20″, and the 23 tires here publish 27.20–27.40″, 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.

Size	Diameter ″	vs 305/30R20	Difference
285/30R20	26.73	-0.47″	-1.7%
245/35R20	26.75	-0.45″	-1.7%
295/30R20	26.97	-0.24″	-0.9%
255/35R20	27.03	-0.18″	-0.7%
225/40R20	27.09	-0.12″	-0.4%
265/35R20	27.30	+0.10″	+0.4%
235/40R20	27.40	+0.20″	+0.7%
315/30R20	27.44	+0.24″	+0.9%
275/35R20	27.58	+0.37″	+1.4%
215/45R20	27.62	+0.41″	+1.5%

How to read 305/30R20

How to read any tire size

How 305/30R20 103Y is printed on the sidewall. It's the most common code among the 23 tires here (17 of them); tires in this size come in other load and speed ratings too.

1305Section width

305 mm across the widest point, or 12.01 inches. Every 305 size

230Aspect ratio

A percentage, not a measurement: the sidewall is 30% as tall as the tire is wide, which is 91.5 mm or 3.60 inches.

3RConstruction

Radial construction.

420Wheel diameter

Mounts on a 20-inch wheel. Approved wheel widths run 10.5″ to 12.0″.

5103Load index

Each tire carries up to 1,929 lb (875 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 1,929 lb each and the standard-load tires up to 1,709 lb, as published.

Specification	Inches	Metric
Overall diameter	27.20	691 mm
Section width	12.01	305 mm
Sidewall height	3.60	91.5 mm
Circumference	85.5	2,171 mm
Revolutions per mile (calculated, unloaded)	741.3	461 per km
Revolutions per mile (published by manufacturers)	763–764	474–475 per km
Approved wheel width	10.5–12.0	267–305 mm

Speedometer error after switching to 305/30R20

Your actual speed– mph

Questions about 305/30R20

What is 305/30R20 in inches?

27.20 inches tall, 12.01 inches wide, on a 20-inch wheel. Written in inches, that is roughly 27.2×12.0R20.

How much does a 305/30R20 tire weigh?

Between 27.8 lb and 35.5 lb for the 23 tires listed here. The lightest is the General G-MAX RS (XL); the heaviest is the Michelin Pilot Sport S 5 (XL).

What wheel width do I need for 305/30R20?

Manufacturers approve 10.5–12.0″ wide wheels for this size.

How many revolutions per mile does a 305/30R20 make?

Published figures run 763–764 revolutions per mile. The calculated figure is 741.3, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 305/30R20 than 225/40R20?

0.12 inches taller on paper (27.20″ vs 27.09″), which raises the axle about 0.06″. Your speedometer will read about 0.4% slow.