[python] Re: Steering Pivots Survey
- From: "25hz" <25hz@xxxxxxxxxx>
- To: <python@xxxxxxxxxxxxx>
- Date: Mon, 18 Sep 2006 22:30:06 -0400
I don't necessarily have the mileage that some of the python builders/riders
have, but I have tried 4 different pivot types.
- sealed bearings. I used 12mm sealed precision bearings pressed into a
steel shell on the BHP. After a little over 2000km it was rock solid,
smooth as when they were installed, no play in the bearings and no "sticky"
or "flat" spots. There is a little play in the pivot because I screwed up
and drilled a 1/2" hole in the bottom pivot bolt flange thinking the 12mm
bearings were 1/2". The slight play is/was minimal and had no effect on
control or ridability and the bearings were not very expensive ones.
- bottom bracket cup and bearings. On Marel's python, the first pivot he
wanted to use was the cup and bearing BB setup from an old 1 piece crank
bike. It worked OK for the first few hundred km, but then the cups started
to deform a little and in the process of continually tightening the BB nuts
to take up the slack, the cups bent more and ended up having to be replaced.
A cartridge BB would likely work better, but the square axle ends were
something I wasn't interested in trying to cobble up a fix for.
- 1/2" female rod ends. I used 1/2" female rod ends on the PC2 because at
the time we were looking for the "perfect" angle to make it easy to learn to
ride the python, but also ebcause I wanted a simple way to build the pivot.
http://www.fleettrikes.com/python%202%20pivot.jpg
After about 1100km or so, the PC2 pivot is every bit as tight as when it ws
first built. In fact, it is slow "breaking in" and is a little tighter than
the BHP was. The tight pivot has no negative effects on steering or
control. The rod ends I used were not really high quality, but they are
working fine with nothing more than an occasional oiling. As a side note,
racing go-carts (that hit 140kph+) and a couple formula 1 Indy cars I looked
over both used 1/2" rod ends, just like I used on the python. While they
are definitely higher quality than mine, the basic strength of the steel in
the ones I used for the pivot, mean that it's probably a few hundred percent
overbuilt. The rest of the pivot consisted of a 3/4" mild steel tube with a
1/2" hole to act as the pivot housing, and the rod ends were simply bolted
through a piece of 1/4" mild steel.
http://www.fleettrikes.com/python%202%20center.jpg
- bike steering head. After removing Marcel's BB pivot, we installed the
steerer tube, cups and bearing form the head tube of a mountain bike. After
a few hundred more kilometers, while the cups are not deforming, the
bearings have slowly hammered small dimples in the cups and the bearing
"settle" into the little dimples when the python front end is straight. It
doesn't cause much of a control issue, it just makes it a little "sticky" to
make small corrections to the left and right on center. If higher quality
bearings and cups were used, the problem might not occur at all.
In the end, if I was to build another python, I'd go back to rod ends
because they are very simple to implement as a pivot, inexpensive, just
about bullet proof, and best of all, they have built in adjustability :)
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