Carl Fogel said:Quoted message said:Quoted message said:>> I just returned from a business trip to Mexico City and I noticed that many of the bikes that
>> the locals were riding around town had two top tubes. One was located in the conventional
>> location and a second located parallel but a couple of inches below the first.
Quoted message said:Quoted message said:Quoted message said:>> Has anyone ever heard of this before? Or, know why?
Quoted message said:Quoted message said:Quoted message said:> I'm going to take a guess that the steel used for the tubing is probably inexpensive therefore
> somewhat 'softer' than what you would find in a 'regular' bike, and that these bikes take a
> hell of a beating over their lifetimes and are made a little stouter than 'regular' bikes. I
> also think that more than a few of these bikes are used commercially, deliveries, small freight
> transport etc. Did you see a brand name on any of them?
Quoted message said:Quoted message said:Quoted message said:I found a picture here:
planeta.commexbike.htmlOpen ↗
Quoted message said:Quoted message said:And here:
benotto.com.mxprincipal.htmlOpen ↗
Quoted message said:Quoted message said:then click on 'Otros Modelos' and then click on the R28.
Quoted message said:That's a weird frame, all right, with two parallel top tubes. But I'm puzzled by what kind of
stress the Mexican designers are trying to resist.
Quoted message said:Do top tubes buckle first?
No but when you only have one size tube available for frames you can double the torsional stiffness
of the frame by adding a parallel tube. This was common in the 1930-40's in the USA. Then there was
a long time when few bicycles were built in the USA and 'English' bicycles were sold to those who
insisted on going against the American idiom and riding bike. About that time a resurgence of racing
grew on French and Italian racing frames and you see to what that lead.
Quoted message said:I can't help wondering whether this double-top-tube design is just wishful thinking, the sort of
thing that Jobst Brandt sometimes points out when he writes about "new" designs that turn out to
have been tried and abandoned a century ago.
Not at all. There is method to this madness.
Quoted message said:The 1916 Morley Bicycle catalogue shows some similar double-top-tube designs:
fixedgeargallery.com04.jpgOpen ↗ fixedgeargallery.com05.jpgOpen ↗
fixedgeargallery.com06.jpgOpen ↗
Quoted message said:Thumbnails of the whole catalogue are at:
fixedgeargallery.commorleyOpen ↗
Quoted message said:But no modern mountain bikes facing heavy bashing or tandems carrying heavy loads use this design,
do they?
We can get good frame tubing in a wide selection of diameters and wall thicknesses today.
Jobst Brandt [email hidden]