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Technical Wheel Information

How to read & understand wheel / rim sizes.

Most vehicle brands have different wheel sizes and as such, it is helpful to understand the make up of the rim/s sizes. The example below will explain what the figures shown on this website, for rims, determine for what vehicle they will fit.  

Example size:  17x8.0|6x139|20

17x8.0 = 17" wheel x 8 inch wide

6x139 = 6 hole rim x 139 pcd (bolt or stud holes as measured by below diagram)

20 = Wheel offset (As explained by below diagram).

TIP: To convert from inch to mm multiply by 25.4. To convert from mm to inch divide by 25.4.

Please take note of the centre bore of the vehicle's hub, as described below. 

Whilst the above size rim may fit your vehicle, note must be made of the tyre size for your specific vehicle, which may be different from the 17" and may be a 16" or other tyre size.

Centre-bore and Hub-centric Rings

This refers to the centre bore in the wheel that centers the wheel on the hub of the car. Since most wheels are mass produced, they have a large centre bore to accommodate several different vehicles.

If there is a vibration problem, it is recommended that you use hub centric rings. Hub rings are hard plastic rings that link the wheel to the vehicle. This centers the wheel and makes your wheel hub centric.

Without hub rings it is possible to get vibrations even if the wheel and tire package is completely balanced.

Wheel Offset

The wheel offset is the distance from the hub mounting surface to the centerline of the wheel. There are three types of offsets.

Positive Offset

A positive offset means the mounting surface of the wheel is positioned in front of the true center-line of the wheel.

Most factory rims will have this type of offset.

Zero Offset

When the hub mounting surface is centered within the rim, it is known as a zero offset.

Negative Offset

If the hub mounting surface is on the brake side of the centre line of the rim, it is considered a negative offset or "deep dish".

Bolt Patterns | PCD 

A wheel's bolt-circle-diameter is the diameter of an imaginary circle drawn through the center of the wheel's mounting-bolt holes. Different vehicle makes and models have varying bolt patterns.

If the pattern has an even number of mounting holes (four, six or eight lugs) simply measure from the center of one stud hole directly across the center of the wheel to the center of an opposite stud hole.

With a five-lug pattern, measure from the center of one stud hole to the center of the farthest stud hole, skipping the adjacent hole. The resulting measurement is slightly smaller than the actual bolt-circle diameter.

For example, a vehicle with a bolt pattern of (5 x 120) means this vehicle's hub has five bolts or lugs, which measure 120 millimeters apart from one another diagonally. Below is a chart on how to measure bolt patterns or PCD..

 

Centre Bore

The centre bore is the size of the hole in the centre of the wheel where the spigot fits through.  The centre bore, (also known as spigot size), is the diameter of this hole, usually measured in millimeters.

 

For most road wheels, the weight of the car is transmitted from the spigot, (the bit the centre of the wheel that protrudes from the hub), to the centre hole in the wheel. The job of the wheel studs or wheel bolts is to hold the wheel in place over the spigot.  

 

It is therefore very important that the centre bore of the wheel matches the spigot size of the car's hub.It is possible to use spigot rings to adapt the size of the centre bore, and spigot rings are available in all the useful sizes.  Of course this only works if the wheels have a larger centre bore than the car's spigot ring.  If the wheel's centre bore is too small, then the only way they could be made to fit would be if they were machined, (i.e. bored out), which is so costly it makes it pretty much impractical.

Staggered Setups:

Many high-performance rear-wheel drive cars, especially BMW and Mercedes sedans, have what are called a "staggered” setup, meaning that the rear wheels are an inch wider than the fronts. This provides for a wider wheel and tyre, and therefore a larger contact patch on the rear drive wheels. This is a wonderful thing, but it requires some attention to detail by the owner. For one thing, it means that the wheels cannot be rotated from back to front, since while the front wheels will fit just fine on the rear, putting the rear wheels on the front will not fit properly and will probably cause the tyres to rub against the suspension. In addition, the front and rear tyres will probably be two different sizes, meaning that care must be taken when buying and mounting tyres to ensure that the sizes are correct and that the correct tyres go on in the correct positions.

Wheel Care

Always keep your wheels clean at all times this way you can protect your investment. Don’t let dust or dirt sit on your wheels this might destroy the finish. Never use steam cleaners or automatic car washes; they can damage your wheels.

The best product to use is a mild soap, cleaning one wheel at a time. Rinse immediately, this way you don’t get a soap scum buildup. Always wait until your wheels are cool before cleaning them.

After the wheels are clean and dry you may add a very light coat of wheel wax to protect your wheels from the elements.

Always use a torque wrench when installing your wheels, it's important to torque the lugs properly. Wheels are frequently over-torqued onto a vehicle's hub bore, which can lead to brake problems or even the lugs breaking right off the wheel.

The best way to torque your wheels is by hand, using a torque wrench. Your owner's manual contains the optimal torque specifications for your vehicle. Always re-torque after your first 100 kilometers.

Wheel Construction

Most alloy wheels are made in one, two or three piece construction types. One piece is a wheel made in a mold as a single piece of metal. Two piece wheels are made of two separate pieces center and barrel that are usually welded or bolted together. Three piece wheels are made of three separate pieces bolted together.

Wheels are manufactured in a variety of ways: Forging, Low pressure Casting and Counter pressure Casting.

Forging

This is the process of forcing a solid billet of aluminum between the forging dies under an extreme amount of pressure. This creates a finished product that is very dense, very strong and therefore very light.

Low Pressure Casting

This is the most common form of rim manufacturing. Liquid metal is poured into a mold and allowed to harden until the finished wheel is cool enough to be taken out of the casting.

Counter Pressure Casting

This method actually sucks the metal into a mold using a vacuum. This reduces impurities making the wheel much stronger than a low pressure cast rim.

Flow Forming Technology

The process begins by pouring molten aluminum into a mold face-side-down followed by rapid cooling. By doing this, the aluminum alloy is condensed and in turn enhances the elastic strength and durability. After the wheel is formed it is pulled from the mold and placed into the flow forming tooling which is similar to the concept of a potters' wheel. This process stretches the barrel to a defined profile and thickness, ultimately giving the wheel its final shape. This "stretching" improves the grain structure of the aluminum making it stronger, lighter and more precise than a non-flow formed barrel resulting in forged aluminum-like strength.

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