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A wheel size is not a single number. A full stamp such as 7Jx16H2 5/120 ET47 66.6 tells you the width and diameter of the rim, the bolt pattern, the offset and the hub bore at a glance, and every one of those five values has to be right for the wheel to fit.

Width and diameter

The first number is the rim width in inches and the second is the diameter in inches. The letter between them describes the bead seat profile, and the number after it is the diameter at the bead seat rather than at the outer lip.

Bolt pattern

Five studs on a 120 mm pitch circle is written as 5/120 or 5×120. It has to match the hub exactly. A pattern that is close but not identical will not centre, and on a car with independent suspension it will load the wheel studs unevenly.

Offset

Offset is measured in millimetres from the mounting face to the true centreline of the wheel. Positive offset pushes the wheel inboard, negative pushes it outboard. Getting this wrong causes rubbing, changes the steering feel and puts load onto the wheel bearings.

Centre bore

The centre bore has to be at least as large as the pilot bore on the hub, and usually has to match it closely so the wheel is located on the hub rather than on the studs alone.

Send us your current stamp, or your vehicle year, make and model, and we will confirm the full fitment before you order.

Both forged and cast wheels start as aluminium, but they do not behave the same way once they are on the car.

How they are made

A cast wheel is poured into a reusable steel mould. A forged wheel is pressed from a billet of solid aluminium under several thousand tonnes of pressure, then machined. Forging aligns the metal grain into the shape of the wheel, so load travels through the part along the direction the metal was worked.

Weight

An equivalent forged wheel typically comes in around 25 percent lighter than a cast wheel of the same size and design. That is unsprung mass removed from each corner, which is where a lot of the real-world benefit comes from.

Strength

The refined grain structure means a forged wheel absorbs an impact better and returns to shape rather than cracking. This matters for kerbing, potholes and track use.

Finish

Machining a face allows far more precise finishing than a painted cast surface. Two-piece and three-piece forged builds also let each section carry a different finish, which is where most of the visual complexity in the aftermarket comes from.

Fitment is where most wheel orders go wrong, and almost all of it comes down to three numbers: offset, clearance and load rating.

Offset and clearance

Moving the offset outward by roughly 3 mm for every extra inch of width is a reasonable starting point, but it is a rule of thumb rather than a guarantee. You still need to check the wheel against the arch, the brake caliper and the steering lock at full lock.

Diameter changes

If you go up in diameter, you normally go down in width to keep the overall rolling diameter the same. That keeps the speedometer and the ABS accurate. Going wider needs more arch clearance and often a lower profile tyre.

Load rating

The load rating is stamped on the wheel and is the maximum weight the wheel is certified to carry. Check it against your vehicle weight per axle, not per wheel. This is the number that matters most on SUVs, pickups and commercial applications, and it is where cheap wheel failures come from.

If you are not sure, send us the vehicle year, make and model plus the sizes you are considering and we will tell you what fits, including when it does not fit.