Tuesday, September 25, 2012

The Italian Geometry

Have you ever wondered why certain bikes have that "special" ride? To many of us, our first great road frame was an Italian frame, probably made in the 1980s or 1990s. We asked Tim K, an avid collector and restorer of Italian bikes, what gave them that special ride: fast for crits but stable for long fast rides.

This is a guest post by Tim K, our resident expert on frame geometry.

From Channone, under CC-BY-2.0.

If you're talking pre-80's (like that Masi in my basement) then Italian geometry is actually very slack compared to an American bike from the same era.  Remember, Italy wasn't very well-paved until the 1980's, so a quick-handling bike would also be brutally uncomfortable, as well as dangerous.  So, angles tended to be a little shallower (around 72 degrees) and chainstays were quite long.  Fork rakes were around 50mm.  Bottom brackets were quite low.

These bikes have an exceedingly pleasant ride.  You can toot around town on them, go touring on them, or get in the drops and really start hammering, all by tweaking stem height a little.  They are not, however, particularly fast, since tons of pedaling energy goes into flexing the frame.

After the 80's, 'criterium style' geometry began influencing cycle design, so the angles tightened up a little to 73 degrees and bottom brackets got a little bit higher.  Fork rake was tightened to about 42-45mm on average.  Chainstays, however, stayed on the longish side.  (Of course, since all bikes back then had long, front-opening dropouts, chainstay length was a variable.)  The angles never got too steep.  74 degrees and above was always the purview of the track bike.

Italy's Strade Bianche - white gravel roads.
Photo credit Luca Violetto. Under CC-SA 2.0 license

Now, the near-universals in Italian geometry are that the angles are always equal (there are exceptions, like Colnago), the top tube is never sloping, and the seat tube tends to be longer than the top tube.  My SOMEC, for example, has a 55cm seat tube and a 53cm top tube.  (Compare to normal American geometry which will vary the angles, but seemingly insists on having the seat and top tubes equal.)

A bike like this (post 80's Italian) will have a slightly counter-intuitive ride.  At slow speeds it is, frankly, twitchy and bordering on difficult to ride.  (I will not ride my SOMEC no-hands at slower speeds.)  Once you get up to a good clip (above 18mph or so), the bike becomes much more stable.  It will hold a line like it's on rails, straight or turning.  The long chainstays provide comfort, but also force the rider to pedal more smoothly, since really jamming down on the pedals will do nothing but make the stays flex.

Naturally, all of this changed when the industry left the steel standard.

OK, that was a bit of a book. :)

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