Oh boy :-(

this   whole discussion is   loaded with   misconceptions (should I  say
"pre-loaded"? :-), comparing  apples to pears  (uhm ...  off-road  motor
bikes  to  Vanagons :-), false   claims  ("pre-loading a  spring does in
effect reduce the number of coils")  and now even mathematical equations
(but as long as nobody shows that  these equations are applicable to the
problem and   what  the  result of   this   application is, mathematical
equations can't really  scare me ...  during  my professional  life I've
just seen too many of them :-)

On Tue, 1998-06-30 09:00:21 -0700, Steven X. Schwenk wrote:

> Sure it will ride higher...but it will also ride stiffer.

Sorry, either -- or!  Either you suppose it to  ride higher, meaning the
loaded spring has the same  length as before, or  you suppose it to ride
stiffer  (by which  -- I assume  --  you mean the  spring  has been more
compressed, but see below).  You just can't eat the apple and keep it at
the same time.  Pick your poison ... :-)

>                                                            And if this is
> not how you pre-laod the spring, then how do you?

I assume   by "pre-loading"  a spring  you   mean to compress   it.  But
compressing  a spring requires  to  apply a force  to  BOTH ends of  the
spring.  If the  force is  missing  at one end,  the  spring will simply
move.  This means that if  the force applied  to  the bottom end of  the
spring (in this case resulting from  the rigidity of the doughnut) lifts
this end an inch, and provided there are no additional forces exerted by
the construction  (in particular  the shock) the  top  end of the spring
will go up  an inch, too, except   you're putting more weight  into your
van.  Only then the spring will get more compressed.

>                                                    And why isn't the
> compressed spring stiffer?

Because  of the simple physical law  that the force  exerted by a simple
spring is proportional to (that is, grows linearly with) the compression
of the spring.   You     CAN  manufacture springs with   a    non-linear
characteristic.  They normally  have different spacing between different
coils (that's what you can easily see) and the  material of each coil is
treated differently thus resulting in different mechanical properties of
each coil (that's  what you can't see  that easily).  Maybe, the springs
in your  bike are of this  sort.  However, the  springs in a Vanagon are
definitely not.

You were asked by some list members to measure the length of your LOADED
springs with and without doughnut.  Did you already do this?  And if you
did, what was the outcome?

Sincerely
 Rainer

 ----------------------------------------------------------------------
| Rainer M Woitok                  | Phone: (+49-9131) 85-7811, -7031  |
| Regionales Rechenzentrum         |                                   |
| Friedrich-Alexander-Universitaet | Fax  : (+49-9131) 30 29 41        |
| Martens-Strasse 1                | Telex: d 629 755 tf erl           |
| D-91058 Erlangen                 |                                   |
| Germany                          | Mail: Woitok@RRZE.Uni-Erlangen.DE |
 ----------------------------------------------------------------------