Chromolly is steel with chromium and molybdenum in the mixture.
("Steel" is any of a number of alloys of iron and other metals.)
When I was a bicyclist in the 1970s/80s, the big thing was Reynolds
tubing. Reynolds 531 was the thing to have. Then they brought out
Reynolds 753, 453, 501 and 500 (amongst others).
Very roughly, the 3 digits referred to the proportions of three of the
various elements included in the alloy (e.g. Reynolds 531 included those
three elements in a ratio of 5:3:1 to each other.)
Also very roughly, it happened that the higher the number, the "better"
the alloy. So 753 was better than 531, and so on.
Some time in the mid - late 80s, I noticed the term "Chromolly" being
used more often. I got the impression that this was a blurring of the
distinction between the various grades, so that a basic chromolly alloy
could be sold as "the same as" a better one - in much the same way as
they used to sell mediocre bikes on the basis of the number of gears
(rather than the range of those gears), and they now sell mediocre bikes
on the basis of front and rear suspension (rather than the quality of
the suspension).
The Pashley MUni has Reynolds tubing, but I note that the stickers only
say "Reynolds Tubing" rather than 531, etc.
Thing is, chromolly is stronger than normal steel, weight for weight,
and is typically used to make bikes lighter rather than stronger. That
means they use less of the steel so the strength is the same but the
weight is reduced. However, the stiffness of the steel is approximately
the same, so, with less of it to be stiff, the chromolly bike frame ends
up more flexible than the standard steel one.
--
Mikefule - Roland Hope School of Unicycling
So many pedestrians tell me I've lost a wheel.
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