How to Calculate PCD (Pitch Circle Diameter)

A short tutorial on Pitch Circle Diameter calculation with a brief explanantion and an example to understand PCD.

Pitch Circle Diameter Calculation

The Pitch Circle Diameter (PCD) is the diameter of an imaginary circular line which passes through the center of all the studs, wheel bolts or wheel rim holes. This "How to calculate PCD tutorial" will help you to learn on What is pitch circle diameter? and its calculation for the given Pitch Circle.

There are two types of Pitch Circle Patterns, the Even Stud Patterns and the Uneven Stud Patterns.
Even Stud Patterns: A pitch circle with even number of studs is called as even stud pattern.
Uneven Stud Patterns: A pitch circle with uneven number of studs is called as uneven stud pattern.
Calculating PCD:
PCD of even stud pattern pitch circle is calculated by measuring from the centers of opposite studs. PCD is usually referred in millimeters.
Sometimes the cap of the wheel will be a hindrance in taking the measurement. For even stud patterns of such cases and for uneven stud patterns, PCD is calculated by measuring the distance between the centers of two adjacent studs, which is termed as "S" and then dividing or multiplying it by below stated numbers as shown.
4 Stud PCD = S/0.7071
5 Stud PCD = S/0.5878
6 Stud PCD = S/0.5
8 Stud PCD = S x 2.613
10 Stud PCD = S x 3.2367
You can also use the standard chart mentioned below to know the "S" measurement value for the given rim size in inches and for the number of studs on pitch circle diameter calculation.

Rim Size	Studs	S	PCD
8" Rim	3	76.90mm	88.8mm
	3	95.26mm	110mm
	4	70.71mm	100mm
	4	71.84mm	101.6mm (4")
	4	81.32mm	115mm
	4	91.92mm	130mm
10" Rim	4	70.71mm	100mm
	4	71.84mm	101.6mm (4")
	4	79.20mm	112mm
	5	65.83mm	112mm
	4	81.32mm	115mm
	4	91.92mm	130mm
	4	98.78mm	139.7mm (51⁄2")
12" Rim	4	70.71mm	100mm
	4	71.84mm	101.6mm (4")
	5	65.83mm	112mm
	4	91.92mm	130mm
	4	98.78mm	139.7mm (51⁄2")
	5	82.29mm	140mm
	5	97.04mm	165.1mm (61⁄2")
13" Rim	4	70.71mm	100mm
	4	79.20mm	112mm
	5	65.83mm	112mm
	4	91.92mm	130mm
	4	98.78mm	139.7mm (51⁄2")
	5	82.29mm	140mm
	5	97.04mm	165.1mm (61⁄2")
14" Rim	4	70.71mm	100mm
	5	65.83mm	112mm
	5	82.29mm	140mm
	5	89.58mm	152.4mm (6")
	6	102.5mm	205mm
16" Rim	5	97.04mm	165.1mm (61⁄2")

Pitch Circle Diameter Calculation Example:

Consider a wheel with 5 studs and the distance between each stud is 89.58 mm. Find the pitch circle diameter of this wheel.

As given above, the formula for calculating PCD for wheels with 5 studs is
5 Stud PCD = S / 0.5878
= 89.58 / 0.5878
= 152.39 mm

Hence the PCD of this 5 studded wheel is 152.39 mm (approximated to 152.4 mm) which is exactly 6 inches.

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