Date: Wed, 1 Jul 1998 12:21:35 +0200
Reply-To: "Dr. Rainer Woitok" <woitok@RRZE.UNI-ERLANGEN.DE>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: "Dr. Rainer Woitok" <woitok@RRZE.UNI-ERLANGEN.DE>
Organization: RRZE (Regionales Rechenzentrum Erlangen)
Subject: Re: Pre-loading Rear Suspension :~o
In-Reply-To: Msg <35990B94.207D00F7@Schwenk-Law.com> of 1998- 6-30 09:00:21
-0700 from sxs@Schwenk-Law.com
Content-Type: text/plain; charset=us-ascii
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 |
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| D-91058 Erlangen | |
| Germany | Mail: Woitok@RRZE.Uni-Erlangen.DE |
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