[python] Re: frame geometry

On Fri Jan 23, 2004 3:41 PM "Peter Oliva" <kaznjammer@xxxxxx>
 
> This leaves a number of interesting questions:
> Do both axles need to be higher then the pivot?
> Does it matter whether the pivot "leans" to the front or the back? (On 
> which side the angle is more narrow?)
> By how much can you change the angle without losing stability?
> Does altering the angle in one direction make steering easier and in the 
> opposite direction increase stability for riding in straight lines?

Thanks Peter and Jurgen for the technical information.
For a typical bike, the stability factors for steering are 
trail and wheel flop.  For a given frame design, these are 
controlled by the design variables of head angle and fork rake.
In the Python design, the front wheel has to fit between the
seat and cranks, so there is not much to do with rake.
We are just left with the head/pivot angle.

In the Python we also have an additional factor for stability: 
the effect of the rising pivot during turning.  We need to condider
how this is controlled by the pivot angle.  Is the lifting effect 
increased or decreased when leaning the pivot angle back?  
Where is the maximum point?  Note that leaning the pivot back 
increases trail for more stability, but it also increases wheel 
flop that can make holding the wheel straight more difficult.

Looking at the pictures it seems that when turning, the
pivot is pulled towards a straight line through both axles.
What happens if the pivot is pulled above that line?
Would the bike then fall over from trying to lean too much?
If that is the case, using a rear wheel that is too small 
could seriously destabilize the bike.

Back to the possibility of a trike rear section, trikes can be 
destabilized by side-loading forces and turning problems 
that do not affect bikes.  It is important how the stability factors 
of trail, wheel flop, and the rising pivot effect trade off with 
respect to design variables such as the pivot angle.  The optimal 
compromise between them for a bike may be significantly 
different than the optimal compromise for a trike.  For example,
it may be necessary to allow more wheel flop in a trike
to avoid buckling while turning.

---Hillel

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

This is the Python Mailinglist at freelists.org

Listmaster: Juergen Mages jmages@xxxxxx

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

Other related posts: