How to Read Wheel Size Numbers: Complete Wheel Specification Decoder

Deconstructing the Code

When you look at an aftermarket wheel specification sheet or the cast markings stamped on the backside of an alloy wheel, you encounter a string of letters and numbers that looks like technical code:

18 x 9.5J ET+22 5x114.3 CB 73.1

Every single element in that alphanumeric string defines a specific mechanical dimension required to verify vehicle compatibility. In this guide, we break down each component step by step.

The Breakdown: What Each Number Means

   18   x   9.5   J    ET+22    5 x 114.3    CB 73.1
   --       ---   -    -----    ---------    -------
   [1]      [2]  [3]    [4]        [5]         [6]

   [1] Rim Diameter (18 inches)
   [2] Nominal Rim Width (9.5 inches)
   [3] Flange Contour Profile ("J" shape for passenger cars)
   [4] Wheel Offset (+22 millimeters from centerline)
   [5] Bolt Pattern / PCD (5 lugs on a 114.3 mm circle)
   [6] Center Bore Hub Diameter (73.1 millimeters)

1. Rim Diameter: "18"

The first number represents the nominal wheel diameter measured in inches across the cylindrical tire bead seating surfaces.

Common passenger car sizes range from 15 inches up to 22 inches.
You must match your tire rim diameter exactly to this number (e.g., an 18-inch tire can only be mounted on an 18-inch wheel).

2. Nominal Rim Width: "9.5"

The second number indicates the width in inches between the inner tire bead retaining seats.

It is not the total physical width from outside lip to outside lip (which is typically approximately 1.0 inch wider due to the outer flanges).
Every tire size has an approved rim width range. For example, a 255/35R18 tire is designed to mount safely on rims between 8.5 and 10.0 inches wide.

3. Rim Flange Profile: "J" (or "JJ", "K", "B")

The letter immediately following the width describes the shape, height, and radius of the wheel's outer retaining lip (flange):

J: The universal standard contour for passenger cars (flange height of approximately 17.5 mm). Nearly 95% of modern street wheels use the J contour.
JJ: Common on older 4x4 trucks and off-road vehicles with taller flange walls (approx. 18.5 mm) for enhanced bead retention during low-tire-pressure rock crawling.
B: Low-profile rim lip historically used on older steel wheels.

4. Wheel Offset: "ET+22" (or "ET22", "+22 mm", "OFFSET 22")

Originating from the German term Einpresstiefe, ET indicates the distance in millimeters from the wheel centerline to the hub mounting pad.

ET+22: Positive offset of 22 mm (hub sits 22 mm outward from centerline).
ET 0: Zero offset (hub pad is aligned directly with the centerline).
ET-12: Negative offset of 12 mm (hub pad is recessed 12 mm into the inner barrel).

Use our Wheel Offset Calculator to instantly compare what moving from your stock offset to a new offset will do to your suspension and fender clearances.

5. Bolt Pattern (PCD): "5x114.3"

The bolt pattern specification consists of two numbers separated by an "x":

First Number (5): The number of wheel lug bolt holes.
Second Number (114.3): The Pitch Circle Diameter (PCD) in millimeters—the diameter of the imaginary circle passing through the exact center of each lug hole.
Common examples: 4x100 (Miata, older Civic), 5x112 (Audi, VW, modern BMW), 5x114.3 (Mustang, modern Civic, Toyota, Nissan), 5x120 (Classic BMW, Camaro), 6x139.7 (Tacoma, Silverado).
Search and compare hundreds of patterns in our Bolt Pattern Chart.

6. Center Bore: "CB 73.1"

Center Bore (CB) is the machined circular diameter of the hole in the exact center of the wheel that fits over your vehicle's axle hub snout:

Vehicle Hubs: Automakers machine their hub snouts to specific sizes (e.g. Honda is 64.1 mm, Toyota car is 60.1 mm, Subaru is 56.1 mm).
Aftermarket Wheels: Manufacturers produce wheels with large universal center bores (such as 73.1 mm or 72.6 mm) so a single wheel model can fit multiple car brands.
When installing wheels with a larger center bore than your car's hub, you must install Hub Centric Rings to center the wheel and prevent highway vibration.

7. Safety Markings & Structural Load Ratings

High-quality forged and cast aluminum wheels feature regulatory safety certification stamps cast into the metal:

JWL (Japan Light Alloy Wheel Standard): Mandatory Japanese government safety standard covering rotational bending fatigue and dynamic radial durability tests.
VIA (Vehicle Inspection Association of Japan): Independent third-party laboratory verification of JWL compliance.
TÜV: Stringent German road safety homologation certifying load limits and manufacturing quality.
Load Rating Stamp: Often stamped as MAX LOAD 690 KG or 1520 LBS. Always verify that your wheel's maximum load rating exceeds half of your vehicle's heaviest axle gross weight rating (GAWR).