Re: [CR]Chainstay length now Bottom Bracket height...Oh No! Not Again...

(Example: Component Manufacturers:Chater-Lea)

To: classicrendezvous@bikelist.org
Date: Fri, 13 Aug 2004 15:43:43 -0400
Subject: Re: [CR]Chainstay length now Bottom Bracket height...Oh No! Not Again...
From: "Richard M Sachs" <richardsachs@juno.com>


snipped: " can't I measure with fair accuracy..."

when i fixture a frame, (CR content: even tho it's not a 1" top tube frame...), i cut the tubes to fit the fixture. once the frame is brazed, i refixture around it and double check against the precsribed numbers. if any at all, the only changes occur in the front center measure - it can shrink .5mm, and in the head angle - it can come by by a minute or three. this is due to heat expansion and contraction. after i refixture around the finished frame, i record the numbers and write them in the book. to tell you the truth, i can't remember any client ever addressing these numbers and saying either 'yea' or 'nea' to what i describe the frame's numbers to be. if i tell a guy it's a 42cm chainstay and he wants to measure it, why does it matter if he uses a rule and i use my fixture? if i measure a 42cm chainstay on a frame and the book says i wrote down 41.75cm, i usually buy myself a pink guitar and listen to adrian balou. ya' know what? there are no guitars here. why? because i went to high school and if the discrepency example i cite here were ever a reality, i would not have finished making the frame. so, when you ask: "...what can't I measure with fair accuracy to double-check what the builder promised?" i assume you meant to write, "...why can't i...", you can measure it. if you're not clear on why a difference may exist, ask the frame's builder. if he tells you his numbers are the centreline ones we've discussed, that will explin why they differ from the ones yielded from the tapemeasure. e-RICHIE chester, ct

On Fri, 13 Aug 2004 12:17:44 -0700 (PDT) Joe Starck <josephbstarck@yahoo.com> writes:


--- Richard M Sachs wrote:


"...typically, all measurements on a bicycle are center to center. fwiw, measuring the key dimensions after it is assembled will not always replicate the 2D ones that were in the frame blueprint."

Richard, I asume you do, as I and others did and/or do, i.e., incorporate every parts variable into the frame design, i.e., lower stack heigth, tire size, rim radius, etc., such that when it's all assembled, tires pumped up, tape shellacked, and what not, THAT A FINAL MEASURING INSPECTION SHOULD JIVE WITH THE BUILDER'S AIM, ELSE HE ERRED.

As earlier discussed with chainstay length, the "effective chainstay length," as Don called it, or the "virtual length," to paraphrase, as you called it, can be double-checked by measuring the actual chainstay length, i.e., hypotenuse, and add half a centimeter or so, ON AN ASSEMBLED BICYCLE. The third dimension isn't at play here.

The only third dimension measurements that aren't on your 2D drawing of note are dropout spacing and all that that entails.

So if I positioned my newly assembled summumbonumboojum bicycle upright on a level surface, approached it from the side(2D as in your drawing) and went to town on it with my tape measure, I'd expect all my measurements taken by me, someone with basic math skills, to jive with da plans.

That said, what can't I measure with fair accuracy to double-check what the builder promised?

Joe Starck summumbonumboojum bicycles Madison, WI

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