What the Stamps on the Back of Your Alloy Wheel Actually Mean

People buy alloy wheels on looks and then discover six weeks later that the offset was wrong, the load rating was too low for a loaded estate, or the bolt pattern was a millimetre out. Nearly all of that is avoidable, because the wheel tells you everything about itself. You just have to know where to look and what you are reading.

Where are the markings on an alloy wheel?

Almost always on the back of the spokes or around the inside of the centre bore. Lie the wheel face down on cardboard and look at the inner barrel and the back of the centre. On some wheels the size is cast into the metal, on others it is stamped or laser etched. Replica and aftermarket wheels sometimes carry a sticker on the inner barrel instead, which is why a refurbished wheel can lose its markings entirely.

If your wheels carry no markings at all, that is worth knowing before you fit them. It usually means they have been refinished and the sticker was stripped, not that the wheel is suspect, but it does mean you are relying on the seller for the specification.

What does 18x8J mean on a wheel?

The first number is the diameter in inches, the second is the width in inches. So 18x8J is an eighteen inch wheel, eight inches wide measured between the inside faces of the bead seats, not the outer edges of the rim.

The J is the flange profile, which describes the shape of the lip that holds the tyre bead. On passenger cars you will see J almost every time. JJ appears on some four wheel drive applications. It is not something you need to match exactly in normal use.

Width matters more than people expect. An inch of extra width moves the tyre roughly half an inch further out and half an inch further in, which is why a wider wheel at the same offset can rub on the inner arch liner. Our guide to staggered fitments covers what happens when front and rear widths differ.

What does ET mean on a wheel?

ET is offset, from the German Einpresstiefe, meaning insertion depth. It is the distance in millimetres between the mounting face of the wheel and its true centre line.

• Positive ET such as ET45 means the mounting face sits outboard of the centre line, pulling the wheel in towards the car. Most front wheel drive and modern European cars run between ET35 and ET50.
• ET0 means the mounting face is exactly on the centre line.
• Negative ET pushes the wheel outwards. You see this on heavily modified cars and some pickups.

A lower ET number pushes the wheel further out of the arch. Drop from ET45 to ET35 and the wheel sits 10mm further out on each side. That is the most common reason a new set fouls an arch liner or a suspension strut. If you are moving wheels between cars with different bolt patterns, read our guide to PCD adapters first, because adapters change effective offset too.

What is PCD or bolt pattern?

PCD stands for pitch circle diameter. 5x112 means five bolt holes arranged on an imaginary circle 112mm across. This has to match your car exactly. There is no tolerance. A 5x112 wheel will not go on a 5x114.3 hub even though the difference is barely two millimetres, because the studs will not line up.

Common European patterns: 5x112 on Audi, Volkswagen, Skoda, SEAT and most modern Mercedes. 5x108 on Ford, Jaguar, Volvo and Land Rover. 5x120 on BMW and Range Rover. 5x100 on older VW and Subaru.

What is centre bore and does it matter?

Centre bore, usually written CB, is the diameter in millimetres of the hole in the middle of the wheel. It has to be the same as, or larger than, the raised hub on your car.

If the wheel bore is larger, you fit spigot rings to take up the gap and centre the wheel properly. If it is smaller, the wheel physically will not go on. Running a wheel without the correct rings is the number one cause of vibration at motorway speed on a brand new set, and we wrote a whole piece on it: do I need spigot rings.

What does MAX LOAD mean and why does it matter?

Max load is the heaviest weight that wheel is rated to carry, per wheel, in kilograms. Multiply by four and you have the maximum the set can support.

This is the marking most people ignore and the one that matters most on heavy cars. A loaded Range Rover or a seven seat SUV with a full boot can be pushing 2,700kg. Divide by four and each wheel needs to carry close to 700kg. A wheel rated at 600kg is not safe on that car no matter how good it looks, which is why heavy applications like our 22 inch Autobiography Turbine style wheels and 20 inch Defender Urban style wheels are built to a different standard from a hatchback wheel.

If a seller cannot tell you the load rating for a wheel going on a heavy vehicle, treat that as a reason to walk away.

What do JWL, VIA and KBA mean?

These are testing and approval marks. They tell you the wheel has been through a recognised structural test programme.

• JWL is the Japan Light Alloy Wheel standard, a mandatory minimum for passenger car wheels sold in Japan and widely adopted elsewhere. It covers impact, bending fatigue and radial fatigue testing.
• VIA means the wheel was tested by an independent Japanese inspection body to JWL standard, rather than self certified by the maker. VIA is a step above JWL on its own.
• KBA is the German Federal Motor Transport Authority approval, followed by a number. German TUV paperwork matters if you are registering a modified car in Germany, and is a strong quality signal everywhere else.

None of these are legally required in the UK or Ireland. All of them are a reasonable proxy for a wheel that has been tested rather than simply cast and shipped.

What else might be stamped on the wheel?

• A date code, often four digits or a month and year, telling you when the wheel was cast.
• A part number, which is how a manufacturer identifies the exact design and finish.
• FLOW FORMED or ROTARY FORGED, meaning the barrel was spun and stretched under heat after casting. This makes the barrel thinner and stronger, taking weight out without losing strength.
• MADE IN and a country of origin.

How to use the markings when you are buying

Write down five numbers off one of your existing wheels: diameter, width, ET, PCD and centre bore. Then check any wheel you are considering against them. If you are moving up a size, the diameter changes and the tyre profile has to come down to keep the rolling radius right, which we covered in are bigger alloy wheels road legal.

If you would rather not do the arithmetic, send us your make, model and year and we will check it against the wheel for you. Every set in our alloy wheel range has its full specification listed, and popular fitments like the 18 inch Concept TTRS style in gunmetal and the 18 inch RS6 C style in gloss black are in stock and ready to go.

Common questions

Can I grind out the centre bore to make a wheel fit?

No. Machining a centre bore is a job for a lathe and a wheel specialist, not an angle grinder. Done badly it removes material from the structural centre of the wheel. Spigot rings solve the opposite problem safely and cost a few pounds.

My wheels have no markings at all. Are they fake?

Not necessarily. Refurbishment strips stickers and can fill shallow stamping with paint or powder coat. It does mean you have no independent record of the load rating, so if the car is heavy, get the specification confirmed by whoever sold them.

Is a higher load rating always better?

It is never worse, but it usually comes with more material and more weight. On a light hatchback a very high load rating just means you are carrying unsprung mass you do not need. Match the rating to the car.

Does offset affect my insurance?

Changing wheel size or offset is a modification and should be declared. We covered exactly what to tell your insurer in do alloy wheels affect your car insurance.

Still not sure what you are looking at? Send us a photo of the back of your wheel on WhatsApp or email sales@omiwheels.com and we will read it for you.