Re: [CR]Measuring BCD -- Newbie Question

Example: Framebuilders:Mario Confente

Date: Mon, 23 Feb 2004 15:07:46 -0800
From: Steve Maas <>
Subject: Re: [CR]Measuring BCD -- Newbie Question
References: <>
In-Reply-To: <>

You don't need charts or anything like that. For five-hole chainrings, the bolt-circle diameter is 1.701 times the center-to-center distance between the holes. A hint for measuring the distance between the holes: instead of trying to eyeball the centers, hold the ruler tangent to both holes and measure the distance between the tangent points.

For 144 mm BCD, the holes are 85 mm apart.

For other numbers of holes, use the general formula,

BCD = d / sin(360/2n)

where d is the distance between bolt holes and n is the number of holes in the chainring.

Steve Maas Long Beach, California wrote:
> Okay gang,
> I have these chainrings up on eBay and it's apparent I need to know how to
> measure BCD. Can somebody explain that to me?
> Many thanks!
> Have tape measurer, will travel,
> Paulie Davis
> Los Angeles