How to read wheel sizes

A single measurement isn't enough for a wheel to fit your car. On the back of the wheel or the inside of a spoke you'll usually find a series of values such as 7Jx17 ET45 5x112 57.1. Each one is a separate fitment requirement, and if even one doesn't match, the wheel either won't fit or won't be safe even if it does.

7J: Wheel width

The first number is the inner width of the wheel, in inches. 7J means a width of 7 inches (177.8 mm). The letter J shows the profile type of the rim edge (flange). Passenger cars almost always use J.

The wheel width must suit the tyre width. For example, a wheel between 5.5 and 7.5 inches is usually suitable for a 205 mm wide tyre. Tyre manufacturers publish the permitted rim width range for each size.

17: Wheel diameter

The number after the x is the wheel diameter in inches. It must be exactly the same as the number after the R on the tyre.

ET45: Offset

ET is short for the German word "Einpresstiefe". It is the distance in millimetres between the wheel's mounting face and the centre line of the wheel.

If you lower the ET by 5 mm, the wheel moves 5 mm outwards on each side. It looks like a small difference, but it can lead to rubbing on the wheel arch, more load on the axle and bearings, and the steering responding differently. It is generally recommended not to go more than ±5 mm away from the factory ET value. We explain the effect of an ET difference with worked examples in a separate guide.

5x112: PCD (bolt pattern)

PCD stands for "Pitch Circle Diameter", the diameter of the circle passing through the centres of the bolt holes.

PCD values commonly seen in Turkey:

This list is only a rough guide. PCD can differ even between models of the same make. Confirm your car's value in the owner's manual or with an authorised service centre.

The PCD must match exactly. A 5x112 wheel cannot be "forced" onto a 5x114.3 hub; even if it goes on, the bolts sit at an angle, which is dangerous.

57.1: Centre bore diameter

This is the diameter of the hole in the middle of the wheel, which sits over the car's hub. On factory wheels this hole is exactly the same diameter as the hub and centres the wheel.

On aftermarket wheels the hole is usually made larger so that it fits many cars. In this case a spigot ring (centring ring) is used. Without the ring, the wheel hangs on the bolts and vibrates, especially at high speed.

Wheel bolt type

The seat of the wheel and the bolt or nut must match:

The bolt thread size (such as M12x1.5, M14x1.5) must also suit the car.

Quick checklist

MeasurementExampleMust match
Width7JWithin the range suitable for the tyre width
Diameter17Exactly the same as the tyre
ET45Within ±5 mm of the factory value
PCD5x112Exactly the same as the car
Centre bore57.1The same, or with a spigot ring
BoltsConical, M14x1.5Suited to the wheel's seat type

More guides

How to read a tyre size, using 205/55 R16 91V as an exampleWhat each part of a sidewall code such as 205/55 R16 91V means, explained with a worked example.The door label: where is your car's factory tyre size shown?How to read the tyre label on the driver's door, why you shouldn't trust the tyres currently fitted, and other ways to find the factory size.Equivalent tyre sizes and the ±3% ruleWhy the overall diameter difference should not exceed 3% when fitting a tyre size other than the factory size, with worked examples.Tyre speed rating and load index tableTables showing how many kilograms each tyre load index number means and how many km/h each speed rating letter stands for.How far does a wheel ET (offset) difference move the wheel?A step-by-step calculation of how far a wheel moves inwards and outwards when you fit a wheel with a different width and ET value.What should your tyre pressure be? Where is the correct value shown?Where to find your car's correct tyre pressure, bar and psi units, and how pressure changes with a loaded car and in winter.