On 10/31/2005 06:03 PM, Ghislain PILLET wrote: > 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 Aha! Thats the reason. I have only a 30mm square tube. OOnly when I put an extra rib under it it became aceptable. > - 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. > > > 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 > > Alternative to aluminium could be carbon ! I might try some day. > > > 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 http://www.matweb.com/tools/weight-calculator.asp) > > 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. > > 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, Well, thanks. Such a frame allows some calculations to be made, but problem is what to do with them. In principle 100kg load is enough, but what happens when riding over a pothole. I would asume, it in a way loads up certain (other) parts of the bike. But how big a forces can be expected here? So I design the bike to hold for what, 200kg? 300kg? a ton? Obviously the more safety the more heavy the bike will get. > and opens a path towards a composite fabrication. Carbon laminated, or > carbon pipes glued in aluminium inserts ? Please, go ahead >:-) Dirk