tireheight.com

205/40R18 in inches

A 205/40R18 tire is 24.5″ tall and 8.1″ wide, and fits a 18″ wheel. In inches it is written 24.5×8.1R18.

Diameter24.46″
Width8.07″
Sidewall3.23″
205/40R18 drawn to scale: 24.46 inch diameter, 3.23 inch sidewall, 18 inch wheel, 8.07 inch tread width18″ wheel3.23″24.46″ overall8.07″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 205/40R18 tires really are

Heights published by BFGoodrich and Michelin for all 3 tires in this size. Their published revolutions per mile work out to 23.7″ under load (below).

Real 205/40R18 tires measure 24.45–24.50″, against 24.46″ from the size code. They run both taller and shorter than the size code.

Height under load23.7″

Published revs per mile (851) mean the tire rolls like a 23.7″ tire on the vehicle. Use this for speedometer calibration.

Weight spread18.9–22.0 lb

The lightest (Michelin Pilot Sport Cup 2 Connect, XL) is 3.1 lb lighter per corner than the heaviest (BFGoodrich g-Force Phenom T/A, XL).

3 tires in 205/40R18

Sort by the spec you care about.

LoadRevs/miSource
Michelin Pilot Sport Cup 2 ConnectPerformanceXL · 86(Y)24.5018.97.21,168851Spec page
Michelin Pilot Sport 4PerformanceXL · 86W24.5020.59.51,168851Spec page
BFGoodrich g-Force Phenom T/APerformanceXL · 86Y24.4522.08.01,168851Spec page

Is 205/40R18 a 24-inch tire?

≈24″

Close. The size code works out to 24.46″, and the 3 tires here publish 24.45–24.50″, so people call it a 24.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

SizeDiameter ″vs 205/40R18Difference
215/35R1823.93-0.53″-2.2%
235/40R1724.40-0.06″-0.2%
215/45R1724.62+0.16″+0.7%
285/30R1824.73+0.28″+1.1%
245/35R1824.75+0.30″+1.2%
215/40R1824.77+0.31″+1.3%
295/30R1824.97+0.51″+2.1%
255/35R1825.03+0.57″+2.3%
225/40R1825.09+0.63″+2.6%
265/35R1825.30+0.85″+3.5%

How to read 205/40R18

How to read any tire size

205/40R18 86Y as printed on the tire sidewall, with each part numbered205/40R18 86Y123456
How 205/40R18 86Y 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.
1205Section width

205 mm across the widest point, or 8.07 inches. Every 205 size

240Aspect ratio

A percentage, not a measurement: the sidewall is 40% as tall as the tire is wide, which is 82.0 mm or 3.23 inches.

3RConstruction

Radial construction.

418Wheel diameter

Mounts on a 18-inch wheel. Approved wheel widths run 7.0″ to 8.0″.

586Load index

Each tire carries up to 1,168 lb (530 kg) at its maximum pressure.

6YSpeed rating

Rated for up to 186 mph sustained.

XLExtra load

Printed after the size.

SpecificationInchesMetric
Overall diameter24.46621 mm
Section width8.07205 mm
Sidewall height3.2382.0 mm
Circumference76.81,952 mm
Revolutions per mile (calculated, unloaded)824.6512 per km
Revolutions per mile (published by manufacturers)851529 per km
Approved wheel width7.0–8.0178–203 mm

Speedometer error after switching to 205/40R18

Your actual speed– mph

Questions about 205/40R18

What is 205/40R18 in inches?

24.46 inches tall, 8.07 inches wide, on a 18-inch wheel. Written in inches, that is roughly 24.5×8.1R18.

How much does a 205/40R18 tire weigh?

Between 18.9 lb and 22.0 lb for the 3 tires listed here. The lightest is the Michelin Pilot Sport Cup 2 Connect (XL); the heaviest is the BFGoodrich g-Force Phenom T/A (XL).

What wheel width do I need for 205/40R18?

Manufacturers approve 7.0–8.0″ wide wheels for this size.

How many revolutions per mile does a 205/40R18 make?

Published figures run 851 revolutions per mile. The calculated figure is 824.6, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 205/40R18 than 215/35R18?

0.53 inches taller on paper (24.46″ vs 23.93″), which raises the axle about 0.27″. Your speedometer will read about 2.2% slow.