[CR]Re: Singer geometry

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In-Reply-To: <000001c3368b$8b540800$59af4943@computer>
References: <000001c3368b$8b540800$59af4943@computer>
Date: Thu, 19 Jun 2003 11:00:08 -0700
To: "goodrichbikes" <goodrichbikes@netzero.net>
From: "Jan Heine" <heine@mindspring.com>
cc: classicrendezvous@bikelist.org
Subject: [CR]Re: Singer geometry


1. It seems that French bikes have low trail figures. The 1948 René Herse (measured by Rebour) in VBQ 3 has 45 mm. 36 mm is low, though. Your suspicion may be correct, and there may be less fork offset. Or the head angle is shallower than I measured.

2. Head angle: I measured the head angle using one of those adjustable triangles engineers use to draw lines at angles. I put the bike on a level surface (measured with a carpenter's level), I placed a plumb (line with heavy nut on bottom) on the head tube, and adjusted the triangle until one side was parallel to the head tube, the other to the string. Obviously, this means I had to eyeball it. What is a bevel protractor?

(I tried one of those spring-loaded tools used in bike shops to measure head angle, but that was so inaccurate that I gave up.)

3. The fork offset is another problem. I didn't remove the fork from the frame. I held a very long metal ruler in the center of the head tube, as best I could, and then measured the distance from the dropouts. But it is easy to see that an error of 1 degree in getting the level parallel to the head tube will result in a significant error of the measurement.

4. Wheel radius is probably as you think - 700C x 26 mm tires (measured width)

So no, I cannot claim these values are correct. It's the best I can do with my limited resources and time.

If you ever are in Seattle, please bring your tools, and we'll measure all my bikes!

Jan Heine, Seattle

P.S.: I am cc'ing the CR list, because I think this is important. I don't want anybody to spec their bike based on my inaccurate measurements!

>I was looking at your 1962 Singer's geo and it seems weird. If your
>measurements are correct and assuming a wheel radius of somewhere
>around 341mm, the trail comes out really low like 36mm. That's too
>low to ride well at speed. How did you measure the head angle? Do
>you have a bevel protractor? If you could accurately measure the
>head angle and the front center, I can calculate the fork offset and
>trail. I suspect the fork offset isn't as large as 71mm.


>Curt Goodrich