Date: Sun, 21 Jun 1998 22:40:38 -0700
Reply-To: "Steven X. Schwenk" <sxs@SCHWENK-LAW.COM>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: "Steven X. Schwenk" <sxs@SCHWENK-LAW.COM>
Subject: Re: Pre-loading Rear Springs re Syncro Suspension (long)
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I still think the spring gets compressed. I will take one last stab at convincing
you. We start with the rear of the van on jackstands, left rear wheel removed and
the shock fully extended with the spring in place. Now, remember, the shock is
fully extended since the wheel is off the ground and there is no weight on the
suspension at all. What do you have to do to remove the spring at this point?
Compress it, right. Why? Because the size of the space the spring fits into is
smaller than the spring and, more importantly, the size of that space is
determined by the length of the shock when it is fully extended, not by the length
of the spring.
Now, if you compress the spring...and then insert a donut on top...and then
uncompress it back into the same space it just occupied...the spring is in fact
compressed further within that space with the donut on top of it than it was
without the donut. How can this not be when the fully extended shock determines
the size or length of the space the spring fits into...remember, the shock is
fully extended at all times since there is no weight on it...
When you put the wheel back on and remove the jack stands, the vehicle sits higher
than it did without the donut(s), not because the donut lifts the van, but because
the spring is stiffer due to the decreased space it has to fit into once the
donut(s) are installed. The sag ...i.e. the amount the suspension compresses by
the weight of the vehicle when it is sitting loaded and static on level
ground...is reduced because the spring is stiffer and it takes more weight to
compress it.
The "lift only" theory overlooks that, in reality, the size of the space the
spring occupies is determined solely by the length of the shock, and that length
never changes no matter how many donuts you insert. The more donuts you use, the
more you have to squeeze/compress the spring in order to fit it into that same
space.
Now do you agree?
steve
SyncroHead@AOL.COM wrote:
> In a message dated 98-06-19 12:14:40 EDT, Drew writes:
>
> > The only way to make the spring more compressed would be to increase the
> > weight of the van. As Steven's understanding (and writing style!) is
>
> Then you could fit 6" of donuts in there. But of course you could not. You
> would have to compress the spring a whole LOT to fit a bunch in there. This
> example takes the logic to a limit and at least implies that reducing the
> space the spring fits into will reduce the installed height of the spring.
>
> I'm just sort of thinking along as I type here and not certain where this
> train of thought will lead...
>
> Perhaps what happens is that the van is raised with each donut until the
> bottom of the suspension is reached. At which point you need to start
> compressing (pre-loading) the spring to get it to fit in. Also, here is where
> you start reducing the height of the spring even before the van's weight is
> applied. Preloading the spring like this causes the spring's action to be
> stiffer and would certainly effect the ride and handling characteristics.
>
> Wait. This just in. After writing the above I continued to read this thread
> before sending and Dave Bayer wrote:
>
> >> Riddle me this: if the spacer were 12" thick would it compress the
> >> spring? I think it would. Therefore, it stands to reason that a 1" thick
> >> spacer would, in fact, compress the spring by some amount, IN SPITE OF
> >> THE WEIGHT BEING THE SAME!
>
> > The 12inch spacer would compress the springs because you would hit
> >the limit of travel. Until you hit the limit of travel, the only other force
> >that will change on the spring is the pull of gravity, but since you are only
> >increasing the distance from the center of the earth to the center of mass
> >of the van by maybe an inch, this is negelible ;) The shock absorbs might
> >behave quite different if they are extended an extra inch at rest, but the
> >springs will not - from the point of reference of the spring, nothing has
> >changed.
>
> I think David just said it better than I did and I concur with him.
>
> Regards,
> Jim Davis
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