Re: [CR] Geometry

(Example: Framebuilding:Paint)

In-Reply-To: <7167B51B6CB844A187CBAD6BA6783E4C@workhorse>
References: <7167B51B6CB844A187CBAD6BA6783E4C@workhorse>
Date: Sun, 12 Apr 2009 13:58:40 -0700
To: Todd Grantham <wtgrantham@comcast.net>, <classicrendezvous@bikelist.org>
From: "Jan Heine" <heine94@earthlink.net>
Subject: Re: [CR] Geometry


At 12:11 PM -0400 4/12/09, Todd Grantham wrote:
>I have 2 separate questions but am submitting them together
>
>1. What is meant by the term "relaxed geometry" used in many
>manufacturers descriptions. I'm sure it refers to angles and maybe
>wheelbase, but can you tell me what range is considered "relaxed" and
>what is considered "unrelaxed".

"Relaxed" geometry refers to a shallower head angle, usually used for rear-loading touring bikes, but there is no accepted definition. For some people, a 72 degrees head angle is "relaxed," but you'll find many racing bikes with that head angle. Others believe anything steeper than 71 degrees is "steep."

"Relaxing" the head angle was an easy way to build a rear-loading touring bike, but we now know that putting the load on the front makes the bike handle better and is easier to balance. However, the best bikes for loaded touring use a 73 degree head angle, which is far from "relaxed" by anybody's definition.

Front-end geometry is a complex topic. Bicycle Quarterly's article "How to Design a Well-Handling Bicycle" covers the basics as we understand them today. (It was published in Bicycle Quarterly Volume 5, No. 3.) There is too much to it to cover here via e-mail - you really need all the drawings and examples to understand what is going on, how you play geometric trail, pneumatic trail and wheel flop against each other.
>2. A few weeks back one of our list member sent pics of a bike he built
>and brazed while attending class in Oregon. I would like to learn lugged
> frame construction and build one for myself someday, but probably can't
>leave my life for 2 weeks to go there and learn. What would be the best
>way for me to proceed?

I am sorry to say it, but it is hard to see how you can become proficient in brazing EVEN IF you spend two weeks full-time at a class. Working metal is a craft that requires a lot of theoretical knowledge, plus a lot of experience. And perhaps some inborn skills (aka as a "touch" for the torch). In two weeks, you can hope to make a first frame and gain some appreciation for all that you don't know.

If somebody told me that they don't speak English, don't know how to ride a bike, and want to publish a cycling magazine, but they don't have 2 weeks to learn all that is involved, I would smile and excuse myself to get back to work.

Many of us have a great interest in how things are done, so Bicycle Quarterly publishes a series called "Builders Speak," where builders show their techniques. Seeing them in a magazine article and being able to emulate them are two different things. It took me months of training to become proficient at working in a machine shop, and the few times I held a torch, I realized that to get good at brazing would take even longer.

I have seen quite a few builders at work, and the best of them have a feel for the torch that allows them to draw the brass (or silver) where they want it, without using too much heat. That proficiency is obtained through years of experience. Just like a good cyclist can ride their bike through a gap barely 4 inches wider than their handlebars. It's not something you pick up from a book.

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