From: tomk@netcom.com (Thomas H. Kunich)
Subject: Re: Summ. of Frame Materials for Review
Date: Mon, 31 Aug 92 21:38:15 GMT
Organization: Netcom - Online Communication Services (408 241-9760 guest)

In article <1992Aug31.203137.10654@hpcvusn.cv.hp.com> harry@cv.hp.com (Harry Phinney) writes:
>tomk@netcom.com (Thomas H. Kunich) writes:
>: I _have_ owned two bikes of almost identical geometries.

>How close were their geometries?

The top tubes and chain stays are the same length. I don't subscribe to
the belief that a degree or two difference in the seat and head tube will
make major differences in the perceived stiffness of the frame.

>This is interesting.  In this part of the country the nervex-lugged 531
>Peugeot PX-10 bikes were regarded as flexi-flyers.  They were built from
>light gauge 531 which was generally 1 gauge number lighter than Columbus
>SL.

Yup, that's the bike. Try comparing it to the alternative metal.
>
>Which stays flex on the large bumps, and how do you know they flex?  The
>rear "triangle" is pretty stiff vertically regardless of tubing
>characteristics.

Ah, but in a turn, if you strike a large bump and the bike tries
to 'stand-up', I assume that the stays have flexed.
>
>Clark And Varney 
>_Physical_Metallurgy_ 
>D.  Van Nostrand, 1962 ISBN: 0-442-01570-4 
>
>Page 198 
>
>An alloy steel may have a higher elastic limit than a plain
>carbon steel, but the modulus of elasticity will be the same, regardless
>of heat treatment.  The solutions to stiffness problems, when steel is
>demanded, is one of design and not metallurgy."
              ^^^^^^^^^^^^^

I am _not_ arguing metalurgy here. I have never seen a frame of any
metal permanently deformed from simple riding. This indicates that 
the yield strength of mild steel used in this manner is sufficiently
strong to not be an issue.

There is the property of tubes that they are stiffer in relationship
to mass than round stock. Doesn't this bear any relationship to
the discussion? And since high strength alloy tubes have progressively
thinner walls does this not have a measureable effect?

>Is this rec.audio?  Someone who acquires a new frame expects it to ride
>better.  This is very similar to the rider who convinces themselves that
>their bike is "whipped", and has gotten more flexible over time.  In
>reality, the bike has not changed stiffness, but rather the rider's
>perception of the bike has changed.

Yes, there are people who believe that their frames have gotten more
flexible with use. I am told that this is most common with bikes
made of Prestige tubing that do get more flexible. I haven't measured
them nor seen any tests to prove it so I'll take that with a grain
of salt until I see it proven or _disproven_.

If this discussion is correct, the additional $600 difference between
a Cromor frame and a TSX frame of otherwise identical geometry is
spent to reduce some 2 or 3 ounces of weight. Is this really the
case? Or are we back to believing Jobst the Grinch and his 
retrotechnology rant -- no one needs more than 4 speeds and tires
smaller than 1 1/4" (oops -- make that 38 mm)? (Just a jap Jobst,
I just don't believe that all technological advances that _I_ don't
use are fectless inconsequencials.)

Newsgroups: rec.bicycles.tech