[python] Fw: Python Modifications Page and PSI Discussion

Hello all,

I would like to forward a mail from Doug Burton,
concerning TT and Cruzbike frame geometry and
the recent "Pedalling Steering Interferences" discussion:

======================================

Sent: Saturday, April 22, 2006 5:01 PM

Dear Jurgen,

I have been very interested in your development work,
and have followed your research for the Airbike and
Python. Thank you for being generous with what you've
learned and for stimulating the discussion of
front-wheel-drive bicycle dynamics.

I am particularly interested in the PSI discussion on
the "Modifications" page of your Python website.

I have been working for about a year on variations on
the Cruzbike kit, which converts a standard Y-frame
mountain bike into a FWD recumbent. You may know of
it. http://www.Cruzbike.com.

I have built two versions of the Cruzbike which have
given me some experiences around the PSI discussion. I
have included photos of them annotated along the lines
of the other photos on your Modifications page. If
they can further stimulate discussion of the PSI
topic, feel free to use them.

Cruzbike 1 had a large distance between the hip line
and the steering axis. It had noteable PSI. I later
modified the seat mount to allow the seat to slide
forward on the top tube. The closer the hip line moved
to the steering axis, the less-noticeable the PSI
became. Note also, persuant to the statement about the
"A-B" distance in the "TT Improved Jurgen Maier"
photo, that Cruzbike 1 has a shorter
crank-to-contact-patch dimension when the hip line was
far from the steering axis. My initial impression is
the hip line effect is stronger than the "A-B"
dimension effect.

Cruzbike 2 was built to use the learnings from
Cruzbike 1, add larger wheels, and reduce weight. The
closer hip line, in concert with very wide handlebars
(673mm wide) has reduced the PSI, but it can still be
felt very slightly.

I am very very interested in what was learned with the
TT Improved Jurgen Maier bike, as my next Cruzbike
experiment is aimed at evaluating the "A-B" dimension
effect on the perception of PSI.

I would welcome your opinions and a discussion of the
dynamics of these interesting bicycles.

Be well,

Doug Burton

Richmond, Virginia, USA

Attachment: Cruzbike2_Lines.jpg
Description: JPEG image

Attachment: Cruzbike1_Lines.jpg
Description: JPEG image

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