RE: [CR]Reynolds 753

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Content-class: urn:content-classes:message
Subject: RE: [CR]Reynolds 753
Date: Thu, 13 Jul 2006 00:29:54 -0700
In-Reply-To: <24d.e0a5994.31e737a3@cs.com>
Thread-Topic: [CR]Reynolds 753
Thread-Index: AcamP13hZglh1eWhQ9CGxHJ0v4DlrAACjbDQ
From: "Mark Bulgier" <Mark@bulgier.net>
To: <Carb7008@cs.com>, <classicrendezvous@bikelist.org>


Jack Romans wrote:
> [...] a vintage bike mechanic and rider told me he
> preferred the ride quality of 531 above all other tube sets
> and 753 bikes were too stiff in comparison.

There's nothing wrong with preferring 531, but you should know that it is almost always stiffer than 753. The only exception would be a 753 tube that is thicker and heavier than the 531 tube you're comparing it to. Both steels came in a range of thicknesses, and the heaviest 753 (tandem or off-road variants) might have been heavier and stiffer than the lightest 531. Not the regular stuff though.

753 is stronger than 531, but not a whit stiffer. And this is important: You can NEVER feel the strength of a tube while riding. (Except by exceeding its strength - and permanently bending or breaking a frame by hard pedaling is really too unusual a situation to bother considering.) The extra strength of 753 allows the builder to make lighter, more flexible frames that are still strong enough.

In fact, 753 typically makes some of the most flexible steel frames ever made. The fact that some people think they are stiff is evidence that most people can't reliably tell if a frame is stiff or flexible.

This gets talked about a lot here, but it bears repeating, because the myth-makers like your mechanic are always at work. The inherent material stiffness property of steel (modulus of elasticity) is very nearly constant - for practical purposes, within the realm of steel used for bike frames, you will not go wrong by assuming the modulus is exactly the same, regardless of alloying, heat-treating and/or cold-working.

For two tubes of the same diameter (as most vintage tubes were), the stiffness and weight will both be proportional to the wall thickness. (I mean, comparing two 1" top tubes to each other, or two 1-1/8" down tubes.) There is no way to make the lighter tube as stiff as the heavier one.

Mark Bulgier
Seattle WA USA