Buying a new chainring

[procerus]

I need to buy a replacement chainring. I want to order it online. Can anyone tell me how chainrings are sized in terms of fitting the crankset's arms?

The site I'm buying from lists the sizes as "110mm PCD 5 Arm" and "130mm PCD 5 Arm" and so on. What does "PCD" refer to and how do I measure it?

I'll reward any replies by asking further dumb questions as I continue the rebuild!

 

[boudreaux]

Originally posted by procerus
I need to buy a replacement chainring. I want to order it online. Can anyone tell me how chainrings are sized in terms of fitting the crankset's arms?

The site I'm buying from lists the sizes as "110mm PCD 5 Arm" and "130mm PCD 5 Arm" and so on. What does "PCD" refer to and how do I measure it?

I'll reward any replies by asking further dumb questions as I continue the rebuild!

It's BCD, and it means Bolt Circle Diameter of the crankarm mounting bolts. It helps to know what cranks you have,but for measuring, with 5 hole crankarms,it's something like the distance between 2 non adjacent holes divided by .95.

 

[serenaslu]

Originally posted by procerus
I need to buy a replacement chainring. I want to order it online. Can anyone tell me how chainrings are sized in terms of fitting the crankset's arms?

The site I'm buying from lists the sizes as "110mm PCD 5 Arm" and "130mm PCD 5 Arm" and so on. What does "PCD" refer to and how do I measure it?

I'll reward any replies by asking further dumb questions as I continue the rebuild!

Here is an excerpt from Performance's website that may help

What replacement chainring do I need?
Chainrings are available in different sizes. To select the correct one, you'll need to know three things:

The number of chainring mounting bolts, either 4 or 5.
The number of teeth on the chainring.
The Bolt Circle Diameter (BCD). The BCD is the diameter of the circle running thru the mounting bolts.
The first two are easy. Just count the bolts attaching the chainring to the crank and count the number of teeth on the ring. The chainring may be stamped with the number of teeth. For the BCD the charts below will help. Measure the distance between the centers of adjacent bolt holes, then refer to the appropriate chart.

For 5-Bolt Chainrings:
Bolt Circle Diameter.............Bolt To Bolt (center to center)
56mm...................................32.9mm
58mm ...................................34.3mm
74mm ...................................43.5mm
94mm ................................... 55.4mm
110mm...................................64.7mm
130mm...................................76.4mm
135mm ................................... 79.5mm
144mm ................................... 84.6mm


For 4-Bolt Chainrings:
Bolt Circle Diameter .............. Bolt To Bolt (center to center)
58mm ................................... 41.0mm
64mm ................................... 45.3mm
68mm ................................... 48.1mm
104mm ................................... 73.6mm
112mm ................................... 79.2mm