Date: Sat, 18 Aug 2007 11:04:14 -0700
Reply-To: Reinhard Vehring <rvehring@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Reinhard Vehring <rvehring@YAHOO.COM>
Subject: Re: ride height adjustment? (long post)
In-Reply-To: <000501c7e1b0$c796f000$15b2d8d1@dhanson>
Content-Type: text/plain; charset=iso-8859-1
Don,
interesting question. I had that very problem in the
extreme at Syncro de Mayo this year, where my van was
perfectly "unbalanced" with 100 % weight on front left
and back right wheels and the other two were up in the
air. I could make it rock back and forth by moving in
my seat. Anyway, my two cents:
The contact force of each tire in a static situation
is determined by the a couple of components. A)
unsprung weight of the suspension parts (wheel,
steering knuckle, control arms) this is minor compared
to the other forces and only becomes more important in
a dynamic situation. B) spring constant and
compression of the coil spring, the most important one
c) spring forces of other suspension components (sway
bar torsion to prevent lean, or preloaded shocks that
have a some compressible gas reservoir) this also is
usually minor.
So it's mostly the spring constant, k, and the spring
compression. Compression is determined by the weight
distribution - the center of gravity.
I don't know the k for vanagon springs. The guys who
claim to have designed lift springs must know, but
they are not telling (now is your opportunity!) But I
can try to estimate: It's probably around 500 N/cm. If
this is about right, loading 250 kg of stuff into the
van ( 4 normal sized guys) would cause an extra force
of 2450 N (613 N per wheel) causing it to sag about 12
mm. Now it would really be interesting to know some
specs on the progressive springs that GoWesty has for
the Syncro...
If I understand you right, you don't want a ride
height adjustment, but rather equalize contact force
(diagonally) to maximize traction. In my humble
opinion, unless you want to break a new record on a
(perfectly flat) race track with you vanagon, that
doesn't matter. I guess this is why there is no way on
a stock vanagon to adjust for that. "Unusual" ways of
trying this would be:
a) Mess with k: Gas bladders in the back that can be
inflated to different pressure, for example, or maybe
different preload on gas shocks. (the two easiest ways
in my opinion)
b) Mess with compression: Onesided spacers. Find out
spring constant, measure diagonal force difference
(with driver in place), calculate spacer thickness for
compensation, machine custom spacer, install, measure
again.
Lot's of work and you can never take a passenger in
the van or drive on anything else but a perfectly
level surface, because it would throw off the balance
again. If I remember right racecars are balanced with
the driver in the car and they don't haul around
camping equipment :-)
By the way, I don't think you can affect front - back
or left - right contact force balance that way at all.
That's just a matter of center of gravity. For example
most Westies sag left. Ride height can be corrected,
contact force cannot. Even if levelled there is more
weight on the left side.
Have fun,
Reinhard
83 "Half-Syncro"-Westy, Moose
--- Don Hanson <dhanson@GORGE.NET> wrote:
> I know, "Check the Archives"...but my dial-up
> connection is so slow that
> when I try to get something odd-ball out of the List
> Archives, it sometimes
> takes me all dang morning to not succeed anyhow.
> Problem: My 84 2wd van seems a bit 'off' in it's
> "stance". It is not
> exactly 'even' in how it sits. With our racecars,
> we called it
> "Corner-balanced". Ideally, each wheel would share
> an equal weight, giving
> you an equal amount of traction at all four tires.
> In reality, most cars
> are heavier at one end or the other..Examples would
> be...say,. the Olds
> Tornado for a heavy front end weight bias and the
> Porsche 911 for a heavy
> rear/front bias.. You can't do much about the F/R
> balance, but you can
> adjust the side to side/corner to corner balance by
> adjusting ride height at
> the wheels. That is what you always hear about on
> NASCAR TV broadcasts when
> they talk about "loose, tight" and making an
> adjustment during a pit
> stop..Those cars have easily accessed ride height
> adjustments that allow a
> crewman to 'tweek' the ride height in a few seconds.
> Many vehicles have
> 'coil over' suspensions, where the springs sit
> around the shock body and
> rest on a threaded spring perch, allowing you to
> adjust the ride height by
> moving the spring perch up or down.
> So my van, if you look closely or pay attention as
> you drive in low
> traction situations, it seems like the left rear and
> the right front wheels
> are taking more load than the other diagonal
> corners..If you can picture the
> van as a table with four legs, it would be like a
> table with un-even
> legs..The table, you'd stick a matchbook under one
> or two legs and it would
> be steady again..The vehicle, you need to extend the
> suspension at one or
> two corners. Or, you would cut off one leg of the
> table to make it stable
> again, or lower a corner of the van..
> Mine, the right rear wheel (or the left front)
> seems "light", so I want
> to either extend that and put more of the load
> there, or lower the left
> rear/right front to allow the right rear and left
> front to carry more load.
> It is a bit difficult to visualize..but hold a book
> parallel to the floor
> and rotate it around a bit, you will see the
> relationship between the
> corners.."corner balance" In a racecar, we used
> four scales and actually
> weighed the load on all four tires, and then
> adjusted the suspension for the
> best balance we could achieve...
> So on a van, is there any way to influence/adjust
> the suspension for
> "length"...Not the right term, I know.."extension?"
> Ride height is the term
> used for racing..but a van is hardly a race
> vehicle..
> Sorry if this has been discussed before and it's
> "in the archives"...
> Don Hanson
>
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