tireheight.com

255/40R18 in inches

A 255/40R18 tire is 26.0″ tall and 10.0″ wide, and fits a 18″ wheel. In inches it is written 26.0×10.0R18.

Diameter26.03″
Width10.04″
Sidewall4.02″
255/40R18 drawn to scale: 26.03 inch diameter, 4.02 inch sidewall, 18 inch wheel, 10.04 inch tread width18″ wheel4.02″26.03″ overall10.04″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 255/40R18 tires really are

Heights published by BFGoodrich, General, Michelin and Toyo for all 20 tires in this size. Their published revolutions per mile work out to 25.2–25.3″ under load (below).

Real 255/40R18 tires measure 26.00–26.10″, against 26.03″ from the size code. They run both taller and shorter than the size code.

Height under load25.2–25.3″

Published revs per mile (798–799) mean the tire rolls like a 25.2–25.3″ tire on the vehicle. Use this for speedometer calibration.

Weight spread22.9–28.5 lb

The lightest (Michelin Pilot Sport 4, XL) is 5.6 lb lighter per corner than the heaviest (BFGoodrich g-Force COMP-2 A/S PLUS, XL).

20 tires in 255/40R18

Sort by the spec you care about.

LoadRevs/miSource
Michelin Pilot Sport 4PerformanceXL · 99Y26.0022.99.01,709799Spec page
Michelin Pilot Sport 5PerformanceXL · 99Y26.0023.79.01,709799Spec page
Michelin Pilot Super SportPerformanceXL · 99(Y)26.0023.79.51,709799Spec page
Michelin Pilot Alpin 5WinterXL · 99H26.0223.99.51,708799Spec page
Michelin Pilot Super SportPerformanceSL · 95(Y)26.0023.910.01,521799Spec page
General G-MAX RSPerformanceXL · 99Y26.0024.210.01,709798Spec page
Michelin Pilot Sport 4PerformanceXL · 99Y26.0024.49.51,709799Spec page
Toyo Proxes Sport 2PerformanceXL · 99(Y)26.0024.99.21,709798Spec page
Toyo Proxes SportPerformanceXL · 99(Y)26.0224.99.41,709798Spec page
Michelin Pilot Sport 3PerformanceXL · 99(Y)26.0025.19.51,709799Spec page
Michelin Pilot Sport 5PerformanceXL · 99W26.0025.39.01,709799Spec page
Michelin Pilot Super SportPerformanceXL · 99(Y)26.0025.310.01,709799Spec page
Michelin Pilot Sport 4 SPerformanceXL · 99(Y)26.0025.89.51,709799Spec page
General G-MAX AS07PerformanceXL · 99W26.0026.110.01,709798Spec page
Michelin X-Ice SnowWinterXL · 99H26.0226.110.51,709799Spec page
Michelin Pilot Sport All-Season 4PerformanceXL · 99Y26.1026.810.01,709798Spec page
Toyo Proxes Sport A/SPerformanceXL · 99Y26.0227.19.61,709798Spec page
BFGoodrich g-Force Phenom T/APerformanceXL · 99Y26.0227.98.51,709799Spec page
Michelin Pilot Sport 4PerformanceXL · 99Y26.0028.49.51,709799Spec page
BFGoodrich g-Force COMP-2 A/S PLUSPerformanceXL · 99W26.0228.59.01,709799Spec page

Is 255/40R18 a 26-inch tire?

≈26″

Yes. The size code works out to 26.03″, and the 20 tires here publish 26.00–26.10″, so people call it a 26.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

SizeDiameter ″vs 255/40R18Difference
215/45R1825.62-0.41″-1.6%
245/40R1825.72-0.31″-1.2%
285/35R1825.85-0.18″-0.7%
335/30R1825.91-0.12″-0.5%
225/45R1825.97-0.06″-0.2%
295/35R1826.13+0.10″+0.4%
235/45R1826.33+0.30″+1.1%
265/40R1826.35+0.31″+1.2%
305/35R1826.41+0.37″+1.4%
215/50R1826.46+0.43″+1.7%

How to read 255/40R18

How to read any tire size

255/40R18 99Y as printed on the tire sidewall, with each part numbered255/40R18 99Y123456
How 255/40R18 99Y is printed on the sidewall. It's the most common code among the 20 tires here (8 of them); tires in this size come in other load and speed ratings too.
1255Section width

255 mm across the widest point, or 10.04 inches. Every 255 size

240Aspect ratio

A percentage, not a measurement: the sidewall is 40% as tall as the tire is wide, which is 102.0 mm or 4.02 inches.

3RConstruction

Radial construction.

418Wheel diameter

Mounts on a 18-inch wheel. Approved wheel widths run 8.5″ to 10.0″.

599Load index

Each tire carries up to 1,709 lb (775 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 1,709 lb each and the standard-load tires up to 1,521 lb, as published.

SpecificationInchesMetric
Overall diameter26.03661 mm
Section width10.04255 mm
Sidewall height4.02102.0 mm
Circumference81.82,077 mm
Revolutions per mile (calculated, unloaded)774.8481 per km
Revolutions per mile (published by manufacturers)798–799496 per km
Approved wheel width8.5–10.0216–254 mm

Speedometer error after switching to 255/40R18

Your actual speed– mph

Questions about 255/40R18

What is 255/40R18 in inches?

26.03 inches tall, 10.04 inches wide, on a 18-inch wheel. Written in inches, that is roughly 26.0×10.0R18.

How much does a 255/40R18 tire weigh?

Between 22.9 lb and 28.5 lb for the 20 tires listed here. The lightest is the Michelin Pilot Sport 4 (XL); the heaviest is the BFGoodrich g-Force COMP-2 A/S PLUS (XL).

What wheel width do I need for 255/40R18?

Manufacturers approve 8.5–10.0″ wide wheels for this size.

How many revolutions per mile does a 255/40R18 make?

Published figures run 798–799 revolutions per mile. The calculated figure is 774.8, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 255/40R18 than 225/45R18?

0.06 inches taller on paper (26.03″ vs 25.97″), which raises the axle about 0.03″. Your speedometer will read about 0.2% slow.