Hello Dirk,
Some extra informations to restore confidence in our mind's readers, about a flexy python I would ride ! (: >)
Forward part of my 20" python is made of steel 30mm x 10 x 1,5.
For the the aft part, I used :
- Central part, steel circular tube diameter 42mm outside, wall thickness 1,5mm
- Rear fork, steel circular tube diam. 22mm outside, wall thick. 1,2mm
I'm quite pleased with the stiffness of the bike. It's quite ok for my 80 kgs.
<x-tad-bigger>
> Could a next forward part version be :
> Aluminium hollow rectangular 30mm x 10mm x 2mm - weight 0,388 kg/m
> length required 1,42m = total weigth 0,55kg
> Pivot and bottom bracket aluminium.
AFAIK aluminium is about three times as weak too. Do you think this
would hold</x-tad-bigger>
Alternative to aluminium could be carbon ! I might try some day.
<x-tad-bigger>> Steel, circular tube 10mm x 1 or 2mm - weight between 0,22 / 0,27 kg/m
> length required 5,25m = total weight 1.31kg
> Pivot and bottom bracket steel.
> (Datas from </x-tad-bigger><x-tad-bigger>http://www.matweb.com/tools/weight-calculator.asp</x-tad-bigger><x-tad-bigger>)
Hey hey stop!!! 10mm x 1mm is 0.11kg/m. I have updated my website with
some values on stresses on the bike, and will base tube thicknesses on
these calculations. ...but even so I do not really expect it really to
be much lighter then my current bike.
</x-tad-bigger>Thanks for opening my eyes : 10mm x mm , 0,11kg/m, is the section you plan to use for your new version.
Your updated website gives me plenty of informations, and opens a path towards a composite fabrication. Carbon laminated, or carbon pipes glued in aluminium inserts ?
<x-tad-bigger>Anyway, if the roads in denmark degrade under a certain level I go for
plan B, I'll spend €€€ for a pantour hub (this is a hub with suspension
build in --- don't know how good it works though).
</x-tad-bigger> Interesting, I've had a look at the Pantour site.
Could it produce what I've seen described elsewhere as a "pogo effect" ?
On my python, I've put washers between the fork and the bracket which holds the bearings to try to eliminate any play. Still 2 or 3 tenths of mm are present and I can feel the longitudinal oscillations of the front part only when I push maximum hard on the pedals. As I cannot hold such an effort for more than a few seconds, it occurs rarely. <x-tad-bigger>
</x-tad-bigger>So, no bother.
