> > Hillary says the Stronglight 49D was introduced in 1936,
The Stronglight aluminum cranks were introduced in 1933 - see Vintage Bicycle Quarterly's Vol. 1, No. 4 about the French technical trials.
They may have been available in Britain starting in 1936... The name 49D was introduced in 1949, when Stronglight was thinking about offering other aluminum crank models.
By the way, the bolt-circle diameter with the five screws was used by
other makers as well. Magistroni made steel cranks with the same
pattern. The Gnutti splined cranks and various French cranks all used
it as well. I am not sure whether they copied Stronglight (so they
could use their aluminum rings), or whether the BCD predates 1933. TA
started by making aluminum chainring, to be used with other makers'
cranks, so it was natural to use the same standard when they
introduced their cranks.
>and according to
> > Joel Metz, the Pro 5 Vis were introduced in 1963.
The TA cranks were introduced in 1960 with the pear-shaped axle and
cotters, but TA switched to a conventional square taper in late 1962.
See the Bicycle Quarterly Vol. 6, No. 1 for TA's company history.
>In that period, there were
>> no better touring cranks. Many bicyclists still like them today for their
>> low width (Q-factor), gearing flexibility, and of course for the fact that
>> they're period correct on many vintage bikes.
Light weight, too. A TA Pro 5 vis weighs significantly less than a
Campagnolo Record carbon crankset.
> > However, their small BCD of 50.4 leads to a fair amount of flexing in
>> larger rings. As Peter White puts it;
>> "Also, the bolt circle is tiny, even for the outer chainring. This allows
>> the outer ring to flex easily to the outside during upshifts, and in time,
>> the gap between the ring and the arm becomes even smaller. As the gap
>> between the outer and middle ring increases, the chain ends up falling
>> between the two. When I was installing the Pro 5 Vis regularly on high end
>> touring bikes in the 1970s, I rarely used outer rings larger than 46 teeth
>> for that reason." That's the reason I don't use them, but as always, YMMV.
>> Use whatever makes you happy.
We looked at this issue. None of my cranks and chainrings have exhibited this phenomenon, even though our Paris-Brest-Paris tandem used a "long chain" and a large gap between chainrings (48-32), as well as brand-new (thinner) chainrings (see below). The "in time" also does not square with physics, just like frames going soft. Either you bend the metal past its yield point, or you don't. I can see that a terrible mis-shift could bend the TA (or any other) chainring, but it hasn't happened on my bikes. I've worn out TA chainrings, but they never have bent outward.
If somebody has a chainring that bent outward in this fashion, I would love to see it. I'll pay shipping, and I'll return it afterward.
Chains can fall between rings if you use a narrow chain with a crankset designed for a wider chain. TA decreased the spacing between their chainrings (as well as the thickness of the rings themselves) to make their cranks compatible with 10-speed.
Jan Heine
Editor
Bicycle Quarterly
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Seattle WA 98122
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