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How To Keep Your Wheels On?

Wheels are a very crucial part of a car and the new car owners should make an informed decision while purchasing them. A wheel has a lot of parts which can be a bit daunting for the new owners. This article provides you detailed information about different parts of a wheel to help you understand them better. 

Width / Diameter

The width of a wheel alignment Kidderminster is measured from the front of the wheel to the back of it. The distance measured is given in inches, the letter J trailing after it. 

The tire bead rides on a cylindrical area. Its diameter is the wheel’s diameter. In simpler words, the area spanning across the face of a wheel is considered the diameter of the wheel. Its unit of measurement is inches. 

The diameter, offset and width of a wheel is what determines the wheel size.

Pitch Circle Diameter

Pitch Circle Diameter, or PCD in short, has two measurements. The first part is pretty easy to comprehend. It indicates how many holes are drilled into the wheel’s centre. Generally, this number varies from 4 to 6. The second part is defined as the diameter which is passed through all the bolt holes/wheel bolts/studs. This measurement is mostly theoretical, which makes it a bit difficult to visualise. 

Stud – It is a piece of large metal that is pierced and projects from the surface, mostly as a decorative piece. 3 studs indicates 3 holes, 4 holes are 4 studs, and so on. 

Pitch Circle – The pitch cylinder’s transverse section which is perpendicular to the axis is called a pitch circle. 

Pitch, Circular – It is the distance spanning over two adjoining holes along the circle of the pitch which is on a plane perpendicular to the axis of rotation. 

How To Calculate Pcd

First, you have to recognise the tyre size or the rim size, as it helps in eliminating the unlikely PCD sizes. Then, take two adjacent studs and measure the distance between them, starting from the hole’s centre. There are PCD calculators online where you can count the stud hole by putting this measurement in millimeters. This gives you the relevant PCD.

Or else, you can manually calculate the PCD by –

  • Dividing the stud distance by 0.7071 for 4 studs.
  • Dividing the stud distance by 0.5878 for 5 studs.
  • Dividing the stud distance by 0.5 for 6 studs.


 Offset is the position of the wheel’s back face where it gets connected to the hub with respect to the hypothetical centre point of the width of the wheel. This measurement is one of the harder ones to envision and even more tough to calculate. The offset determines the position of the wheel in the wheel arch. 

All the wheels being sold nowadays are made of alloy, which means the probability of getting negative or zero offset is very unlikely. There will always be a positive offset to some extent. 

An array of acceptable offsets is provided by all vehicles for any wheel diameter. But, if the offset is not suitable for the vehicle–it is too low or high–the wheel might jut out of the wheel arch or get tangled with the brake calipers in the wheel. 

Centre Bore

A hole present on the back of the wheel is where the wheel is attached to the wheel hub of the vehicle. The diameter of this hole is known as the centre bore. 

In original equipment wheels, the vehicle’s hub diameter and wheel’s centre bore are the same. But it is not the case for aftermarket wheels. The size of their centre bore is larger than that of the wheel hub of the vehicle as a lot of vehicles are constructed with a different hub diameter, PCD remaining the same.

‘Spigot ring’ is used to make up for the size difference. These rings are very easy to find and are sold in most fitting kits provided by car servicing Kidderminster. The main purpose of the spigot ring is to reduce the centre bore’s size to match the size as needed by the car. 


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