• From: Paul Cartwright <paulcartwrightx@xxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Fri, 24 Feb 2012 11:32:47 -0500

This is my first post. I have been enjoying reading about all your
projects, so I thought I'd share one of my own.
Here is a photo of a python-like bike I built.  I thought it might be
interesting to you all, since although it is not low to the ground like the
python, it has many similar features.  I designed this bike before I saw
the python, so it was interesting that after considerable experimentation,
I arrived at some similar aspects of the design.  For example, the optimum
angle of the steering tube (my angle is 64 degrees).

I have been surprised at the frequent mention in emails about how it takes
a while to learn to ride the low-racer. My bike is relatively easy to ride.
 Although it does handle differently from an upright bike, some people have
got the hang of it in twenty minutes.  I can ride comfortably slow or fast,
and it will ride in a circle of 2 meters radius easily once you have
practiced a bit.  One reason for this is the short wheelbase, 95cm.  I had
thought that the lower the center of gravity the easier it would be to
ride.  But of course I found out that higher is easier because of the
"reverse pendulum effect".  Thus, with a seat height of 76 cm, my bike puts
my eyes level with drivers of those noisy and sometimes unobservant motor
vehicles, and also makes my bike quite maneuverable.  Mounting and
dismounting is very easy, as well as stopping at traffic signals, etc.,
since you can sit comfortably on the seat with one or both feet on the

The negative trail is only 7cm, so there is not much seat rise when you
turn, and yet, the bike still tracks nicely.  I have now taken this bike on
lots of rides, often for 35km at a time, often over rough, unpaved roads.
 The seat is really comfortable and pretty easy to make.  It is welded up
out of other bicycle parts (mountain bike forks and stays), with two chair
shaped side rails and inner tubes stretched across to the desired tension.
 This was so much easier than building suspension into the bike frame.
 Also the seat is adjustable fore and aft for different sized riders.

The crank (BB) height is 61cm, (15cm below the seat), which I like because
it keeps my hardworking legs lower than the rest of me, which would seem to
be a more natural position, more like walking or running.  Also, although
it is less aerodynamic, I have opted for a somewhat upright back position,
because I like to have my neck/head in line with my back.  When coasting
down a hill at 25, this bike is even with a traditional road bike with the
rider's hands on the upper handlebar.  But one could build this bike with a
more reclined (hence more aerodynamic) seat.  This would perhaps make it
comparable in speed to other designs.

I have used 27" wheels because with a large diameter they seem better to me
for rough surfaces.  And perhaps there is a little better road traction
than a smaller diameter wheel.

There is almost no pedal steering interference.
The weight distribution of bike plus rider is 97 pounds on the front wheel
and 78 pounds on the rear wheel.
It looks like the bike would flip forward if you jammed on the brakes, but
this does not ever happen.  The rear wheel will skid if you use only the
rear brake.
Going up a very steep hill, especially with sand or snow, the front wheel
 will slip.  But usually at this point I would be happy to walk and push
the bike up hill.

If there is interest I can try to make a video and post it.
Happy riding,

Attachment: blue bike 1 DSC_8761.JPG
Description: JPEG image

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