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My Pythonesque Lowracer Project
In the Fall of 2003, I became interested in lowracers and began contemplating building one for myself.
While I was intrigued by front wheel drive flex chain lowracers (e.g., Tri-Sled Nitro, ZOX20) and would still like to build one sometime, I was particularly interested in the Knakker lowracer variant of the Flevobike with the center-pivot steering. Then in early January 2004, I stumbled across the webpage of Jürgen Mages' center-pivot steered Python and decided to build my own variant.
The main differences between the Knakker and the Python seem to be steering angle (45º with positive trail in the Knakker vs 70º with negative trail in the Python) and front wheel size (20" limiting the Knakker to 5 gear ratios vs 26" permitting 10+ gears in the Python). Although I was intrigued by the design of the original Python, I decided to make some changes (are they improvements?):
- Steering pivot: The Python's steering pivot was made from a bottom bracket and shell with crank arms attaching the bottom bracket axle to the back half of the bike, but I decided to use a convential head tube, steerer tube, and headset instead. While I at first wanted to have the head tube attached to the back half of the bike and the steerer tube to the front, I eventually concluded that the reverse would work better.
- Front frame: The front half of the Python was made of two large (10 x 40 x 1.5 mm) steel beams welded to the bottom bracket shell and extending forward to carry the dropouts for the front wheel and support the cranks in front of the wheel. I prefer triangulated frames to cantilevers and so decided to
use a triangulated space frame of small tubes instead of the big steel beams. This would allow me to use part of the rear triangle of a 27"/700C donor bicycle without much modification.
- Front wheel: The Python used a 26" wheel from a mountain bike, but I decided to use a 700C wheel and a narrow high pressure clincher [I like going fast!].
- Rear wheel: The Python used a 26" wheel from a mountain bike, but I decided to use a 20" wheel [with narrow high pressure tire] so as to shorten the wheelbase. This may decrease the turning radius.
- Handlebars: The Python lacked handlebars and the brake and gear shift levers were hidden beneath the seat. I like handlebars on my bicycles and so decided to use upward swept underseat handlebars supporting brake levers and bar-end gear shifters. I did consider high handlebars extending back from the space frame, but decided against them.
I view the lowracer as an experiment and in order to reduce cost and effort I have decided to use donor bikes and mild steel tubing. If the experiment is a success, then a more refined (i.e., lighter and more expensive) version could be made with better materials (e.g., cromoly tubing). I am busy scrounging donor bikes, and so far I have a 27" 10-speed with 3 piece cottered crank and the fork of a 20" BMX bike. I'm also preparing to order a quantity of square section metric mild steel tubing to weld up the space frame, rear spar, rear brace, seat braces, etc.
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