Joe wrote: "(Is this within Don's 6-9 mm axle/hanger edict?)"
I'd just like to point out that it is not *my* edict, but it is a range called out on Campagnolo, Shimano, and SRAM frame specifications. The amount varies with hanger length; the shorter the hanger, the more narrow the window. Based on my own experience with DS MTB's (sorry Dale), it seems to be widely disregarded, but since CS&S see fit to call it out, I think it's probably worthwhile to keep in mind especially considering todays 9 & 10 speed cassettes.
Also, I think it's almost universally accepted that when talking about frame geometry, chainstay length is called out as the straight line distance between the BB center and the axle center (not parallel to the ground). The terminology used to describe the dimension is confusing. A horizontal measurement is always parallel to the ground. A vertical measurement is always perpendicular to the ground. A "Parallel" dimension is one that travels from point to point and may include both horizontal and vertical elements e.g., measuring along the hypotenuse of a triangle.
When considering balance while designing a frame, it's easier, for me, to determine the required chainstay length by considering only the horizontal distance from BB center to axle center. That horizontal distance is what I like to call the "effective" chainstay length. To illustrate my point, a 420mm chainstay length as parallel measurement (the way it's typically given in frame specs) puts the axle in a different position depending on BB drop. As drop increases the chainstays effectively shorten and vice versa. Cheers! Don Ferris Anvil Bikeworks, Inc. Littleton, Colorado Ph: 303.471.7533 / 303.919.9073 Fax: 413.556.6825 http://www.anvilbikes.com
-----Original Message-----
From: classicrendezvous-bounces@bikelist.org
[mailto:classicrendezvous-bounces@bikelist.org] On Behalf Of Joe Starck
Sent: Wednesday, August 11, 2004 3:02 PM
To: classicrendezvous@bikelist.org
Subject: Re: [CR]Re: measuring stay lengths
"my way of measuring (measuring along the centerline of the frame's central plane) yields the half cm diff that you note, not the 1 ephgrave mm that you not after the fact. "
Richard,
Let's consider a 42 cm chainstay length and 8 cm drop.
Side view of the frame:
The designated chainstay length is 42 cm measured from center of bottom bracket to center of rear axle, PARALLEL TO THE GROUND, and the rear axle position is achieved by default on a vertical dropout, whereas with the use of a horizontal, it's anywhere the builder prescribes, in my case, it was always to the midway position that the axle could be positioned in the dropout, using primarily 1010B or shorter horizontals (Is this within Don's 6-9 mm axle/hanger edict?)
Now then, this above set-up on a frame jig means that the measurement along the somewhat centerline of the chainstay, I say "somewhat because the dropout center is 'neath it, measured from center of BB to center of axle position, should be set at a bit less than 42.7 mm, being the hypotenuse of the 42 cm leg of the triangle.
So, say 6 mm difference there.
Now then,
Top view of the frame:
Same 42 mm length, and yet the hypotenuse leg is a wee bit shorter, by about one millimeter. And when measured from outside of crank bolt to outside of skewer the differnce is less, as the measurement is now close to being parallel to the plane of the main triangle. But who cares about the top view, right? It was this dimension I was thinking about when I stated the one ducky difference, and so I yes, I contradicted myself , but in err' only. My bad.
Still, I would think that if a Sachs owner (Is Richard Cielec a Sachs owner?) were to measure his chainstay length from outside of crank bolt to outside of skewer, center to center, and came up with 42.5 on an 8 cm or so BB-drop-designed frame of yours, subtracted 5mm netting 42 cm, he has indeed measured his chainstay length quite nicely and precisely.
Starck, Joe
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