Forbes- Actual thickness is kind of hard to determine with common implements and no damage. But some understandings are possible with a bit of education and experament. The tone a tapped tube makes is a function of diameter, wall, damping elements (and other factors). So taping a known tube of the same diameter then comparing to the frame in question give a thicker/thinner reference. I think I have a feel for the heat transfer rate when I grab a tube, again not a measurement. The seat post diameter is not a reliable indicator of ST wall. The heat of production can distort way more then wall thickness differences and reaming is often "to fit". One actual measurement that you can try is to use a Vernier caliper down a water boss, then measure across the diameter plus the boss, difference is one wall (kind of). The weight of a frame is another general indicator.
Andy Stewart
Raleigh, NC
----- Original Message ----- >
> Date: Wed, 7 Jan 2009 15:26:05 -0800
> From: Forbes Bagatelle-Black <diarmaede@yahoo.com>
> To: <classicrendezvous@bikelist.org>
> Subject: [CR]Re: 1978 Proteus catalog
> Message-ID: <755789.92676.qm@web56906.mail.re3.yahoo.com>
> In-Reply-To: <MONKEYFOODniSnRMWuL000001de@monkeyfood.nt.phred.org>
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> Reply-To: diarmaede@yahoo.com
> Message: 4
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>
>> From: Andrew R Stewart <onetenth@earthlink.net>
>>
>> Hey all- Here's a link to my Flicker site and the set
>> of scans from a aprox.
>> 1978 Proteus Design catalog...
>> http://www.flickr.com/
>
> Hi Andrew and All,
>
> Thanks, Andrew, for that timely post! I just bought an old Proteus frame.
> The seller thought he could dig up the original build list, but no luck.
>
> My geometry appears to indicate a custom build. The seat tube is 68cm,
> c-to-c, and the top tube is a "much too short" 59cm, but the price was
> such a steal, I figured I'd use my 150mm Salsa stem and call it good.
>
> The tubing decal gives me no indication as to whether they used the
> heavy-duty R531 tubing. I sure hope they did, or this bike could be
> whippy as all git out. Anyone know of a way I can find out about tubing
> wall thicknesses?
>
> Sincerely,
>
> - Forbes Black, Santa Clarita, CA