What's is PCD
PCD stands for (pitch circle diameter), this is the diameter of a circle drawn through the center of your wheel's bolt holes. PCD is measured in millimetres and also indicates the number of studs or bolts the wheel will have. 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. Wheelfire.com has a fitment program that calculates this for you.
What is Offset (ET)
Your car requires a unique offset. This is where the wheel will sit in relation to the bodyline of the vehicle, realistically you can go 5-7mm outside these recommendations, but always consult a technician if you are unsure, as there are often other factors that need to be considered. Offset is usually stamped on the wheel and is measured in millimetres of et (et is the short form of the German word 'Einpresstiefe' which literally translates as insertion depth).
Positive Offset A positive offset means the mounting surface of the wheel is positioned in front of the true centerline 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.
If the hub mounting surface is on the brake side of the center line of the rim, it is considered a negative offset or "deep dish".
What is Hubsize/center boreThis refers to the center bore in the wheel that centers the wheel on the hub of the car. Since most wheels are mass produced, they have a large center 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/aluminium 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.
Noise and Vibration ProblemsSome of the most common causes of noise and vibration problems (There could be others):
• Tire and wheel out of balance
• No hub centric rings on aftermarket wheels
• Incorrect hardware for aftermarket wheels
• Irregular tire wear
• Rim is damaged
• Tire is damaged
Do not ignore pulling or vibration. If you have this problem have a professional inspect the issue.