Alloy Wheels - Buying Guide

Alloy wheels have been multiplying in recent years with manufacturers putting them on base models if just for looks. When buying alloy wheels there is far more to it then just appearances. Alloy wheels are usually cast from a mixture of aluminum and other metal compounds to provide a light yet strong rim. Forged alloy wheels make for an even lighter wheel and greater strength but do come at a price!

Alloy wheels are more asthetically pleasing, lighter, and better at dissipating brake heat than steel alternatives, making them ideal on performance cars. Handling and acceleration can also be imporved by fitting a lighter set of alloy wheels. Unsprung mass is the weight of a vehicle that is not supported by the suspension - wheels, tires and brakes. The rotational mass of the wheel is also reduced resulting in more responsive acceleration and braking.

Alloy Wheel Fitment

It is vital to have alloy wheels that fit correctly. Handling characteristics are affected by offset, as well as plus sizing. The majority of people do increase the size of wheel over the OEM wheels. Most cars can take a size increase of 2 inches, with work often required for anything more than this. running low profile tyres allows the rolling radius to be kept the same - meaning the gearing remains true along with the speedometer reading. A low profile tyre means that the side wall will be more shallow increasing responsiveness but will lower the ride quality.

The wheel offset is the distance the hub mounting surface to the centerline of the wheel.

Zero Offset - The hub mounting surface is even with the centerline of the wheel.

Positive - The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.

Negative - The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.

Many japanese cars have an offset around ET45

If the offset of the wheel is not correct for the car, the handling can be adversely affected. When the width of the wheel changes, the offset also changes numerically. If the offset were to stay the same while you added width, the additional width would be split evenly between the inside and outside. For most cars, this won't work correctly.

The PCD is the pitch circle diameter. This dicates how the wheel bolt holes line up so it is important that this is correct too. A common PCD of 4x100 would meant 4 bolt holes drilled through the centre of a 100mm circle. Another common PCD is 5x114.3 - 5 bolt holes drilled through the centre of a 114.3mm circle.

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