PCD

PCD is the pitch circle diameter, a measurement that defines where bolt holes sit on a wheel, hub, or flange. It is not the diameter of the bolt holes themselves, but rather the diameter of an imaginary circle running through the center point of each hole. A wheel with a PCD of 120 mm has its five or six bolt holes arranged on a circle 120 mm across. Get this dimension wrong and the wheel will not fit the hub, no matter how hard you force it.

PCD is always paired with a bolt count. You will see it written as 5x120 or PCD 120/5H, meaning five bolts on a 120 mm circle. Common automotive PCDs include 98, 100, 105, 110, 112, 114.3, 120, and 130 mm. Metric and imperial overlap: 114.3 mm is equivalent to 4.5 inches, a legacy standard still in use. Most vehicles use five or six bolts; light trailers and small equipment may use four.

The term sits at the intersection of wheel fitment and manufacturing precision. Wheel spacers and adapters exist because PCD does not vary; the measurement is locked into both the vehicle hub and the wheel casting. A hub with 5x120 cannot accept a 5x114.3 wheel without an adapter that repositions the bolt holes. Manufacturers must hold PCD tolerance to within 0.5 mm or tighter during wheel casting and hub machining, since cumulative error across multiple fastening points will cause runout, vibration, or seating failure.

Where confusion arises

PCD is often confused with bore diameter, which is the hole at the center of the wheel that slides onto the hub's axle. A wheel can have the correct PCD but the wrong bore, and it will not mount safely. Offset, backspacing, and bolt pattern are separate specifications; PCD defines only the circle on which holes are placed, not how far the wheel extends from the hub or how thick the spokes are.

In practical workshop use, PCD matters most when sourcing replacement wheels, adapting hubs between vehicle platforms, or diagnosing why a wheel is loose or damaged at the bolt holes. Measuring PCD requires the distance between any two bolt holes and a formula based on bolt count, or direct measurement of the circle itself using a ruler or caliper against the hole centers. Misidentification is common in secondhand parts markets and is a frequent cause of unsafe assembly.