To measure the Pitch Circle Diameter (PCD) on rotors, you are essentially measuring the diameter of the circle that passes through the center of all the bolt holes or studs. This measurement is crucial to ensure the rotor matches the bolt pattern of your vehicle's hub. The method depends on the number of bolt holes or studs on the rotor.
Here's how to measure the PCD based on common bolt patterns, incorporating information from the reference:
Measuring PCD Based on the Number of Studs or Bolt Holes
The process for measuring a rotor's PCD is the same as measuring a wheel or hub's PCD, focusing on the bolt pattern on the rotor hat that connects to the hub.
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For Rotors with an Even Number of Studs or Bolt Holes (e.g., 4, 6, 8):
- Locate two bolt holes directly opposite each other across the center of the rotor.
- According to the reference, the P.C.D. can be measured from the inside of one hole directly across to the outside of the hole opposite.
- This measurement gives you the diameter of the circle passing through the bolt centers.
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For Rotors with Three Studs or Bolt Holes:
- Locate any two bolt holes that are next to each other.
- Measure the distance between the centers of these two adjacent holes.
- According to the reference, you then multiply this measurement by 1.154 to calculate the P.C.D.
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For Rotors with Five Studs or Bolt Holes:
- The reference indicates that the method of measuring between two holes next to each other is also used for five-stud patterns.
- Measure the distance between the centers of any two adjacent bolt holes.
- Note: While the reference mentions this method for five-stud, it only provides the multiplication factor (1.154) specifically for three-stud patterns. A different factor is required for five-stud patterns, which is not provided in the reference.
Knowing the correct PCD is essential for selecting compatible brake rotors for your vehicle. Always double-check your vehicle's specifications or measure the existing hub/rotor carefully.
