RE: [CR]Was: intro... now: frame geometry

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From: "Ken Freeman" <freesound@comcast.net>
To: "'Jan Heine'" <heine94@earthlink.net>, "'ternst'" <ternst1@cox.net>, <damann@mitre.org>, <classicrendezvous@bikelist.org>, <oroboyz@aol.com>
References: <F016848C232375449D66E2D139DFED2F01B2A62C@IMCSRV4.MITRE.ORG> <8C9693BA807914E-7EC-7D4F@webmail-de18.sysops.aol.com> <000001c79b31$68080f90$6501a8c0@maincomputer> <8C9694D9B4EB4F3-1E8-80AE@webmail-db05.sysops.aol.com> <000d01c79b3d$df203a10$6501a8c0@maincomputer> <8C969562C736E1A-1B04-8141@MBLK-M03.sysops.aol.com> <002a01c79b40$44b95f80$0300a8c0@D8XCLL51> <a06230944c276c3eed436@[192.168.1.33]>
Subject: RE: [CR]Was: intro... now: frame geometry
Date: Sun, 20 May 2007 23:59:37 -0400
In-Reply-To:
Thread-Index: AcebWjfd/UJdH1UZTimnhcTq23J+1wAAZnPQ


Jan if you trace back through the thread, no assertion was made that chainstay is a critical aspect of handling. How to measure chainstay was the question.

I agree with what you're saying, it's just that you're responding to a question that was not part of the thread originally.

Ken Freeman Ann Arbor, MI USA

-----Original Message----- From: Jan Heine [mailto:heine94@earthlink.net] Sent: Sunday, May 20, 2007 11:43 PM To: ternst; freesound@comcast.net; damann@mitre.org; classicrendezvous@bikelist.org; oroboyz@aol.com Subject: Re: [CR]Was: intro... now: frame geometry

Measuring chainstay length: I think there are two logical ways of doing it:

1. If you are reporting on the handling of a certain bike, it might make sense to report the length from BB center to the actual location of the axle center. After all, that is what the length is when you ride the bike.

2. However, Bicycle Quarterly usually reports the range in which you can adjust the length, for example, 430-450 mm. The user then can pick their preferred chainstay length.

I don't want to open a can of worms, but chainstay length seems relatively unimportant among the factors that influence a bike's handling. I have ridden two bikes with the same geometry, except the chainstay length varied by 20 mm, and they handled so similar that I could not tell a difference. I also have moved the rear wheel in the dropout slots on the same bike by as much as 15 mm, and could not tell the difference.

When you think of it in terms of the total wheelbase (which is what will affect the handling), then even 20 mm are only 2% of a 1000 mm wheelbase. That is not a great change as far as overall length or weight distribution is concerned.

Chainstay length may play a more important role in comfort, as the from the vertical plane of the seat (think a plumb line from the seat) to the rear axle is pretty short, so 20 mm can make a significant difference in how much your seat lifts as your rear wheel hits a bump.

Jan Heine
Editor
Bicycle Quarterly
140 Lakeside Ave #C
Seattle WA 98122
http://www.bikequarterly.com