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305/40R23 in inches

A 305/40R23 tire is 32.6″ tall and 12.0″ wide, and fits a 23″ wheel. In inches it is written 32.6×12.0R23.

Diameter32.61″
Width12.01″
Sidewall4.80″
305/40R23 drawn to scale: 32.61 inch diameter, 4.80 inch sidewall, 23 inch wheel, 12.01 inch tread width23″ wheel4.80″32.61″ overall12.01″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 305/40R23 tires really are

Heights published by General for the one tire in this size. Their published revolutions per mile work out to 31.7″ under load (below).

The one tire listed, the General G-MAX AS07, measures 32.60″: 0.01″ shorter than the size code's 32.61″.

Height under load31.7″

Published revs per mile (637) mean the tire rolls like a 31.7″ tire on the vehicle. Use this for speedometer calibration.

1 tire in 305/40R23

Sort by the spec you care about.

LoadRevs/miSource
General G-MAX AS07PerformanceXL · 115V32.6039.011.02,679637Spec page

Is 305/40R23 a 33-inch tire?

≈33″

Close. The size code works out to 32.61″, and the 1 tire here publishes 32.60″, so people call it a 33.

All 33-inch tire sizes, on every wheel size.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

SizeDiameter ″vs 305/40R23Difference
325/35R2331.96-0.65″-2.0%
285/40R2331.98-0.63″-1.9%
295/35R2432.13-0.48″-1.5%
325/40R2232.24-0.37″-1.1%
305/35R2432.41-0.20″-0.6%
265/50R2232.43-0.17″-0.5%
305/45R2232.81+0.20″+0.6%
275/50R2232.83+0.22″+0.7%
285/40R2432.98+0.37″+1.1%
33×12.50R2233.00+0.39″+1.2%

How to read 305/40R23

How to read any tire size

305/40R23 115V as printed on the tire sidewall, with each part numbered305/40R23 115V123456
How 305/40R23 115V 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.
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.

423Wheel diameter

Mounts on a 23-inch wheel. Approved wheel widths run 10.0″ to 12.0″.

5115Load index

Each tire carries up to 2,679 lb (1,215 kg) at its maximum pressure.

6VSpeed rating

Rated for up to 149 mph sustained.

XLExtra load

Printed after the size.

SpecificationInchesMetric
Overall diameter32.61828 mm
Section width12.01305 mm
Sidewall height4.80122.0 mm
Circumference102.42,602 mm
Revolutions per mile (calculated, unloaded)618.5384 per km
Revolutions per mile (published by manufacturers)637396 per km
Approved wheel width10.0–12.0254–305 mm

Speedometer error after switching to 305/40R23

Your actual speed– mph

Questions about 305/40R23

What is 305/40R23 in inches?

32.61 inches tall, 12.01 inches wide, on a 23-inch wheel. Written in inches, that is roughly 32.6×12.0R23.

What wheel width do I need for 305/40R23?

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

How many revolutions per mile does a 305/40R23 make?

Published figures run 637 revolutions per mile. The calculated figure is 618.5, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 305/40R23 than 285/40R23?

0.63 inches taller on paper (32.61″ vs 31.98″), which raises the axle about 0.31″. Your speedometer will read about 2.0% slow.