11 replies to this topic

[Ducati996Senna]

Does anyone know the PCD measurement for the VX?

[Steve Crisp]

110 x 5

[Robski]

PCD?

[johnvx220]

Is that the policeman that nearly got me yesterday?

[Steve Crisp]

I think it stands for Pitch Circle Diameter - the diameter of the pitch circle, ie twice the distance from the axis to the pitch point. Mercedes is 112 PCD (as Ricky knows, as he has Mercedes-type Superleggra's and "wobble bolts" to make up tht 2mm. Steve

[cyberman]

I think it stands for Pitch Circle Diameter - the diameter of the pitch circle, ie twice the distance from the axis to the pitch point.

In case anyone is in doubt http://www.metricati...ering/gears.htm defines this as follows (and a number of other related terms). There is an illustrative diagram at the link which did not import into this response.


Metric Gears
Metric gears are defined by the module system, as follows:

Module
The length in mm of the pitch circle diameter per tooth.
MOD = PCD / N

Number of Teeth
The number of teeth on the gear.
N = PCD / MOD

Pitch Circle Diameter
The diameter of the pitch circle.
PCD = N x MOD

Outside Diameter
The outside diameter of the gear.
OD = (N + 2) x MOD

Center Distance
The distance between the axes of two gears in mesh.
C = PCD(g) + PCD(p)

Circular Pitch
The distance between adjacent teeth measured along the arc at the pitch circle diameter.
CP = x MOD

Circular Tooth Thickness
The width of a tooth measured along the arc at the pitch circle diameter.
CTT = CP / 2

Addendum
The height of the tooth above the pitch circle diameter.
A = MOD

Dedendum
The depth of the tooth below the pitch circle diameter.
D = H - A

Whole Depth
The total depth of the space between adjacent teeth.
Finer than 1.25 MOD:
H = 2.4 x MOD

1.25 MOD and coarser:
H = 2.25 x MOD

Kind regards - Ian

[jneill]

That's very helpful. But what does it mean?

[nonterraquous]

From http://www.preludecr...e/wheelspec.php

PCD (Pitch Circle Diameter). To obtain this measurement (see diagram), draw a circle which passes through the centre of each wheel stud/bolt hole. Now draw a line from the centre of a wheel stud/bolt hole to the opposite side of the circle (crossing through the centre of the circle) - The distance of that line is the PCD (in mm).

Offset is also described on that page too

Scott.

Edited by nonterraquous, 25 January 2004 - 08:06 PM.

[jneill]

But what does it MEAN? Is a PCD of 110 "a good thing". If so, why? (Sorry, but I'm definately not an engineer...)

[Jestersdead]

I don't think PCD can be good or bad, its just a dimension.

[Steve Crisp]

A PCD of 110mm is only a good thing if manufacturers make loads of gorgous, lightweight, shiny wide wheels in all sizes with this PCD. If they don't, then it's not so good!

[Robski]

Ahhh, now it all seems to make sense! BAD thing then....