Double step, wide range, evenly spaced gearing for SRAM hub.


Doug Goncz

Hello, rbt crowd.

With the cooperation of Jobst Brandt and Carl Fogel in thread "Exact Ratio...",
I have recomputed my dream gear set.

It is a double step front in which the ratio betwen low, middle and high is the
same as the ratio of the rear hub, allowing for the possibility of a standard
three speed front with overdrive at the rear whenever the front steps are
inadequate. Further, each rear step is one half of a front step. The quadratic
nature of wind resistance notwithstanding, this transmission is designed so
that there are as many duplicates as possible, with the widest possible range,
completely in opposition to conventional wisdom.

The idea is to implement microcontroller coordination of the gear set such that
the rider need only be warned by a beep tone with one of two natures, rising to
indicate a standard upshift, and falling to indicate a standard downshift.
Shifting to a duplicate might be warned by a chirp tone, like a cricket, but
the duplicates are nearly exact, within a few percent, so the rider wouldn't
notice *unless* there were a lack of synchronization, and that can be adjusted
and programmed out.

I ride a double step 21 speed wide range with the same basic properties but an
11-34 evenly spaced rear, not on a planetary hub, on my Thunderbolt and I will
stand here and tell you that with real terrain, real muscles, and real weather,
a racing gear set is not what most riders want. No normal person needs to tune
their pace to coordinate maximum forward progress with the limits of wind
resistance. Closely spaced top gears are for riders on flat terrain with no
wind, pushing hard. These are real-world gears. Try them and tell me they are

0.73 / 1 / 1.36 gives
(18.4) 25 34 46 (62.6) front to be used with
(35) 30 26 22 19 16 14 12 rear

the feel of this is an average of less than 5% away from ideally even spacing.
I checked hundreds of combinations.

The 35 gear is optional. On an eight speed Dual Drive, it's worth the extra
money. On an old seven speed Torpedo, you just use the 12-30 cogs.

Look at the success of the evenly spaced but overdesigned Rohloff 14 speed hub
with a fraction of the range on my Thunderbolt if you don't get it. This
transmission has a decade of range, near 1000%, compared to about 435% for the
Rohloff. You never run out of gear, fast or slow, climbing or descending,
headwind or tail.

To hell with tradition. Let's try something new. Something computer generated,
computer controlled, rational in the extreme, transparent even.

Given time, I will implement this transmission. Until then, for a year, I am
reserving patent rights to this development. It took a lot of work. After a
year, the patent application would be rejected for prior publication.

Authors in rbt prior to today's date who have used their real names are exempt
from prosecution, with license to implement this invention prepatent during the
waiting period. Anybody else, including SRAM and Shimano, is fair game.

This post constitutes reduction to practice, the primary requirement for
patentablity. With 7,000 posts in Usenet, authorship, the other, is no problem.
And documentation of this development is solid. There are dozens of carefully
saved versions with dates on CD already out.

For any of you who'd like my bicycle files on CD, along with a permitted copy
of Mathcad 6.0, feel free to write. Mathsoft will be happy to give you a demo
of 6.0, a copyable demo diskette, if they have one, but they probably don't. I
do have such a diskette, and an email from Mathsoft giving permission to share
my work with a copy of the Mathcad 6.0 distribution CD.

For them, distribution of such an old version with so much accompanying,
personalized demo material is not a problem. It won't cut in to the market for
the much more capable version 11. It will only increase the market for the
latest version by introducing new users to the sofware.

I have purposely refused to upgrade my Mathcad year after year to retain this
distribution right, which grows more free and less threatening to Mathsoft with
each year that goes by and each version that they release.

I even have the manual, and am willing to lend it person to person. Do not copy
the manual. That copyright expires some 50 years after Mathsoft goes out of
business, and that simply hasn't happened. Please respect the effort involved
in generating physical, printed work.

Doug Goncz ( )
Student member SAE for one year.
I love: Dona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.
I drive: A double-step Thunderbolt with 657% range.