From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Gearing theory
Date: 31 Aug 1999 20:48:21 GMT

Ted Stevenson writes:

> Just bought a used Pinarello with all DuraAce components. I'm
> curious about the gearing on this bike. In particular, the
> chainwheels are 53/42 (I should know the freewheel counts, but all I
> can say for sure right now is that the biggest cog (on this 7-speed
> freewheel) is 24.)

Half step gearing was used in the days before 5-9 speed clusters when
fewer sprockets gave such a limited number of gears that each one was
used as an upper or lower ratio by using one of two closely spaced
chainrings.  Hence half step gearing has a one or two tooth jump on
the rear and a three or four tooth step on the front.  If you look at
a gear chart of half step, you'll find a reasonably uniform
progression for double shifts, down in front--up in back--up in
front--up in back--down in front-- etc.

Ever since five and six speed clusters were introduced, the method is
to use the big chainwheel in the front for the outer four to five
sprockets in the rear for flatland, and the inner four to five
sprockets with the small chainwheel for climbing.  Shifting a
chainwheel takes more than three times as long a shifting a sprocket
in the rear (the rotational speed ratio does this) and double shifts
even longer.  Don't do it.

Because 42 was the smallest chainwheel old style Campagnolo cranks
would carry (due to half step gearing of the time), the 42-52 was a
natural progression from the half step.  If you can fit a smaller
sprocket on your cranks, do so.  Don't worry about redundant gears in
the overlap region.  You don't need all those gears anyway in spite of
what the believers in continuously variable gears say.

Jobst Brandt      <jbrandt@hpl.hp.com>