Help on alloy wheels with our Alloy Wheel Guide

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Alloy Wheels Guide

Alloy wheels are made from an alloy of aluminium or magnesium metals (or sometimes a mixture of both). They are lighter than traditional steel wheels and as a result improve the speed and steering of cars. Most new cars come with steel wheels as standard unless it is a luxury car. Alloy wheels are normally an expensive add on option.

Why put Alloy Wheels on your car?

There are two main reason why people put alloys on their cars:

1. Performance
Cornering is much better with alloys because alloy wheels allow tyres to have wider rims and smaller sidewalls. When a car takes a corner fast, the sidewalls are deformed by the enormous pressures. If the sidewalls are smaller, there is less deformity in the tyre allowing greater speed and performance.

Alloy wheels are also better heat conductors than steel wheels. This improves heat dissipation from the brakes, which in turn reduces the chance of brake failure in more demanding driving conditions.

2. Styling
There is no doubt that alloy wheels look much better on cars than the standard factory fitted wheels.

Alloy Wheels Glossary

PCD
Pitch Circle Diameter is normally measured in millimetres. For a 4 or 6 bolt car, this is the distance between the centre of two diametrically opposite bolts. In the 4-bolt picture to the left, this would be the distance between holes 1 and 4. It is slightly different to work out the PCD for a 5-bolt pattern: draw a line between two neighbouring bolts, and draw a line from the midpoint of this line to the opposite bolt. Repeat this with a different set of three bolts, and the two long lines will cross in the centre, thereby making the distance between this intersection and the centre of a bolt the radius of the bolt circle. The PCD would be twice the radius.

    

The PCD of a wheel is normally displayed with the number of bolts. For example, 5/100 is a wheel with 5 bolts and a PCD of 100mm. When manufacturers design around imperial values, you might see 4/4.5" (4/114.3mm). Our wheels use the metric system.

PCD can also be caluclated using this formula:
PCD = d / SIN(180/n)
where n = number of bolts and d = centre distance between two adjacent bolts

Centre bore
The centre bore of a wheel, measured in millimetres, is the size of the hole in the centre of the back of the wheel. This is the part the wheel that mounts onto the axle spigot (mounting hub) of the car. It is essential that the wheel has a centre bore that fits the axle spigot or the centre bore is adapted with a ring to fit the axle spigot. This is the load bearing part of the axle so the centre bore must fit the axle spigot exactly. Wheels that have a centre bore which exactly match the axle spigot are known as hubcentric wheels. Other wheels which have centre bores larger than the axle spigot are known as lugcentric wheels. These wheels come with spigot location rings (hubcentric rings) which lock or slide into the back of the wheel. They are usually made of hard plastic or steel. We supply spigot location rings with our alloys, if required.

Offset (ET)
The offset, measured in millimetres, is the distance from the hub-mounting surface to the true centreline of the rim. This value can be positive or negative. A positive offset describes a wheel where the hub-mounting side is closer to the outside edge of the wheel. A negative offset describes a wheel where the hub-mounting surface is closer to the inside edge of the wheel. This will make the wheel stick outwards more than inwards. When choosing wheels, a wheel with not enough positive offset will be closer to the wheel arch, and one with too much positive offset will be closer to the suspension components.

The offset value will be stamped on the wheel as an ET number. For example, ET42 will mean an offset of 42mm. If this is the specification given by the car manufacturer then you can normally get away with up to 5mm-7mm difference when choosing new alloys.

It is important to have the correct offset. Otherwise the wheel might srcub against the suspension or bodywork. It may also affect the steering so it becomes too heavy or the wheels will not self-centre, meaning that you will be fighting to keep the car going straight!

Wheel Size
The wheel size, measured in inches, is the diameter of the wheel where the beads of the tyre seat on the wheel. This measurement does not include the rim flange.