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305/40R20 in inches

A 305/40R20 tire is 29.6″ tall and 12.0″ wide, and fits a 20″ wheel. In inches it is written 29.6×12.0R20.

Diameter29.61″
Width12.01″
Sidewall4.80″
305/40R20 drawn to scale: 29.61 inch diameter, 4.80 inch sidewall, 20 inch wheel, 12.01 inch tread width20″ wheel4.80″29.61″ overall12.01″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 305/40R20 tires really are

Heights published by Michelin for all 3 tires in this size. Their published revolutions per mile work out to 28.7″ under load (below).

Real 305/40R20 tires measure 29.60–29.61″, against 29.61″ from the size code. They run both taller and shorter than the size code.

Height under load28.7″

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

Weight spread34.9–39.1 lb

The lightest (Michelin Pilot Sport 4 SUV, XL) is 4.2 lb lighter per corner than the heaviest (Michelin X-Ice Snow, XL).

3 tires in 305/40R20

Sort by the spec you care about.

LoadRevs/miSource
Michelin Pilot Sport 4 SUVPerformanceXL · 112Y29.6034.99.52,469702Spec page
Michelin Pilot Alpin 5WinterXL · 112V29.6135.710.52,469702Spec page
Michelin X-Ice SnowWinterXL · 112T29.6139.110.52,469702Spec page

Is 305/40R20 a 30-inch tire?

≈30″

Close. The size code works out to 29.61″, and the 3 tires here publish 29.60–29.61″, 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.

SizeDiameter ″vs 305/40R20Difference
285/40R2028.98-0.63″-2.1%
255/45R2029.04-0.57″-1.9%
235/50R2029.25-0.35″-1.2%
295/40R2029.29-0.31″-1.1%
265/45R2029.39-0.22″-0.7%
245/50R2029.65+0.04″+0.1%
275/45R2029.74+0.14″+0.5%
255/50R2030.04+0.43″+1.5%
285/45R2030.10+0.49″+1.7%
235/55R2030.18+0.57″+1.9%

How to read 305/40R20

How to read any tire size

305/40R20 112V as printed on the tire sidewall, with each part numbered305/40R20 112V123456
How 305/40R20 112V is printed on the sidewall. It's the most common code among the 3 tires here (1 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

240Aspect ratio

A percentage, not a measurement: the sidewall is 40% as tall as the tire is wide, which is 122.0 mm or 4.80 inches.

3RConstruction

Radial construction.

420Wheel diameter

Mounts on a 20-inch wheel. Approved wheel widths run 10.0″ to 12.0″.

5112Load index

Each tire carries up to 2,469 lb (1,120 kg) at its maximum pressure.

6VSpeed rating

Rated for up to 149 mph sustained.

XLExtra load

Printed after the size.

SpecificationInchesMetric
Overall diameter29.61752 mm
Section width12.01305 mm
Sidewall height4.80122.0 mm
Circumference93.02,362 mm
Revolutions per mile (calculated, unloaded)681.2423 per km
Revolutions per mile (published by manufacturers)702436 per km
Approved wheel width10.0–12.0254–305 mm

Speedometer error after switching to 305/40R20

Your actual speed– mph

Questions about 305/40R20

What is 305/40R20 in inches?

29.61 inches tall, 12.01 inches wide, on a 20-inch wheel. Written in inches, that is roughly 29.6×12.0R20.

How much does a 305/40R20 tire weigh?

Between 34.9 lb and 39.1 lb for the 3 tires listed here. The lightest is the Michelin Pilot Sport 4 SUV (XL); the heaviest is the Michelin X-Ice Snow (XL).

What wheel width do I need for 305/40R20?

Manufacturers approve 10.0–12.0″ wide wheels for this size.

How many revolutions per mile does a 305/40R20 make?

Published figures run 702 revolutions per mile. The calculated figure is 681.2, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 305/40R20 than 265/45R20?

0.22 inches taller on paper (29.61″ vs 29.39″), which raises the axle about 0.11″. Your speedometer will read about 0.7% slow.