From: harry@cv.hp.com (Harry Phinney)
Subject: Re: Automatic transmissions for bikes
Organization: Hewlett-Packard Company, Corvallis, Oregon USA
X-Newsreader: Tin 1.1 PL4
Date: Mon, 28 Dec 1992 19:34:02 GMT

marc@gauss.math.mcgill.ca (Marc Sokolowski) writes:
: The computer is to be equipped with a software that will adapt the
: shift pattern to the terrain and physical abilities of the cyclist, in order
: to keep him pedaling at an efficient 75 rpm.

And what makes him believe that 75 rpm is most efficient under all
circumstances for all riders? 

: 	Well, the point that a transmission is needed in high-performance
: bikes is a sure sign that human muscles don't provide a flat performance
: curve at all "pulses", just like a typical explosion engine at all rpm's,
: and I don't see why a sophisticated shifting algorithm wouldn't be able to
: at least approach the optimal way of shifting.

The transmission will have to be prescient.  It must know how long a
hill is, whether it is about to steepen, whether you intend to start
sprinting, how hard you wish to ride, your current state of fatigue,
etc.

: Besides, my personal experience makes me sick of having to shift,
: especially when I am suffering from high exhaustion on the way up a 20% hill.

Perhaps you should try a newer shifting set up such as Shimano's STI
with Hyperglide.  I think you will be surprised at how simple and quick
shifting can be.  No form of automatic shifter can lessen the power
required to climb a steep hill at a given speed.

: After all, the auto that is described in Popular Mechanics simply
: translates to being able to pedal from 0 to 3000 rpm without loss of torque,
: as seen from the point of view of the wheels (max torque being at 75 rpm
: from the cyclist's perspective).

Even if we accept the assertion that 75 rpm is always the cyclist's
torque peak (which, BTW, I do not believe), the bike rider does not
necessarily wish to be pedaling at their torque peak rpm at all times.
For instance, there are times I wish to maximize power rather than
torque, which requires significantly higher RPMs.

: 	For me it is inevitable that not only autos will become a
: significant portion of bikes, including race bikes, but will very rapidly
: dominate, with only high quality manual transmissions surviving in high-end
: equipement.

While I can imagine some sort of automatic transmission possibly being
popular for commuting bikes, I have yet to hear of any sort which would
be appropriate for racing.  Note the distinct absence of automatics from
automobile racing (yes, I do remember Jim Hall's Chaparrals).

: This because bikes are getting more and more popular for a
: boring task called commuting, and because of the similarity of evolution
: with cars, as autos got extremely popular (at least in NA) when high torque
: V6 and V8's that became available starting in the 50's only needed 3 forward
: speeds.

So now that we have larger, stronger, higher-torque bike riders the
automatic transmission becomes more practical, right?

The automotive torque converter effectively provides a wider range of
drive ratio than the transmission alone, but at some loss of efficiency.
Also note that even 4 spd/OD automatic transmissions suffer a loss of
efficiency compared to manual transmissions.

: BTW: For cars, I *HATE* automatics, because there is still decreased
: performance (but I'll go for a tiptronic any day!) and increased fuel use,

But you will gladly suffer such a loss of performance and increased 
energy usage when _you_ are the engine?  I think not.

: This is a different story for a bike as
: infinitely more work is involved given you are the engine.

Exactly.  I believe riders will be reluctant to accept even a small loss
of efficiency.  Note that convenient enclosed-shaft drive bicycles have
been built and marketed in the past, but that the more efficient chain
drive dominates.

Harry Phinney   harry@hp-pcd.cv.hp.com
Newsgroups: rec.bicycles.misc,rec.bicycles.tech,aus.bicycles