Date: Tue, 30 Jun 1998 15:17:18 -0400
Reply-To: Derek Drew <drew@INTERPORT.NET>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: Derek Drew <drew@INTERPORT.NET>
Subject: Re: Pre-loading Rear Suspension :~o
In-Reply-To: <359881B7.C06A591F@Schwenk-Law.com>
Content-Type: text/plain; charset="us-ascii"
My comments are sprinkled below...
At 11:12 PM 6/29/98 -0700, you wrote:
>I will kill this thread if requested. However, it is an important topic
>and the issue at hand remains unresolved. This post proposes a means to
>resolve the dispute. It's worth the effore because if adding a spacer
>pre-loads the springs, then there's a cheap, relatively easy and
>accurate way to tune the suspension...balance it...and yes, improve it.
>In fact, there should be no dispute that you can accommplish these goals
>by pre-loading each wheel to the optimal level of spring
>pre-load/suspension sag given the weight the wheel bears and the damping
>provided by the boges. The stock set up is not the optimal set up, but
>is too soft and unbalanced...The the damping of the boges really isn't
>that bad...just needs a little more spring. The issue, then, is, does
>inserting a spacer pre-load the spring or not, or must something else be
>done instead?
>
>The majority opinion says inserting a spacer only raises the van height
>by the thickness of the spacer without affecting spring or suspension
>characteristics. The dissenting opinion says, no, that's wrong; when
>you insert the spacer between the spring perches, you compress the
>spring within the perches, so that even with no weight on it, it is
>compressed further than with no spacer at any given point in the
>suspension travel, and hence stifferr than without the spacer.
>
>The majority opinion is erroneous in that it assumes that inserting a
>spacer between the spring and top perch is the same as simply placing a
>spacer on top of a free-standing spring ... which just lifts the van and
>does not change the spring at all. The majority's mistake is in not
>taking into consideration that the spring is confined within spring
>perches of a limited maximum length that does not change when the spacer
>is added.
your confusion begins with the above sentence
>By inserting the spacer between the spring and the top spring
>perch, you compress the spring by the width of the spacer,
only when there is no weight on the spring. under almost all normal
conditions, you do not compress the spring by the width of the spacer
>and it is
>compressed that much further at any given point in the travel over what
>it would be without the spacer
wrong. it is only compressed further when the shock is at full extension.
>...and it is this compressed spring's
>characteristics you are starting out with, not the same, free standing
>spring with just a spacer sitting on top of it.
>
>The conceptual key here is to visualize the suspension completely
>unloaded.
The conceptual trap here is to visualize the suspension completely
unloaded.
>Now put the full weight of the van on it. How much does it
>sag? Next, insert the spacer...now, when you put the full weight of the
>van on the suspension, how much does the suspension sag?...less than
>without the spacer
wrong
>because the spring is stiffer
wrong
>because it starts out
>already slightly compressed.
wrong. The word "because" above appears to be at the root of your problem.
>..just like putting a stiffer spring in a
>scale...the weight sinks it less.
wrong
>We can resolve the controversey by answering two questions. (1) does
>inserting a donut compress/shorten the spring?
It does when the shock is at full extension; otherwise it does not. The
shock is rarely at full extension unless Jim Davis, Tim Smith, or myself is
at the wheel driving on uneven terrain.
you think the extra compression somehow gets stuck on the spring and
applies to the spring even after the shock is compressed; this does not happen
>(2) If so, is a spring
>that is compressed or pre-loaded or shortened by, say, two inches (the
>width of the spacer) any different in its characteristics/stiffness than
>a stock, uncompressed spring? Alternatively phrased, isn't it true that
>the last, say, 8 inches of travel of a spring with 10 inches of travel
>is stiffer than the first 8 inches of travel? By stiffer, I mean it
>will provide less sag under the same weight, will be slightly harder to
>compress and will rebound slightly quicker....and will feel frimer.
meltdown
>Once these two issues are resolved, we can either move on to determining
>the optimal amount of pre-load for each wheel, or figure out how to
>pre-load if not this way.
>
>steve
pre-wash the pre-load
________________________________________________________
Derek Drew New York, NY & Washington, DC
drew@interport.net
'90 Syncro Westfalia...
...seen off-road at http://www.tiu.net/~des/vw/drew/index.html
Also seen at: http://www.pipeline.com/~tforhan/swrange.htm
http://4wd.sofcom.com/VW/snow.html
http://www.pipeline.com/~tforhan/swmassn.htm
http://4wd.sofcom.com/VW/Campers/Campers.html
Note: most valuable Vanagon sites on the planet (for owners) are:
http://gerry.vanagon.com/cgi-bin/wa.exe?S1=vanagon
ftp://gerry.vanagon.com/pub/
