Date: Thu, 18 Jun 1998 00:48:14 -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: Pre-loading Rear Springs re Syncro Suspension (long)
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With a vehicle as neat and versatile as a vw syncro, good suspension is
almost a necessity to fully utilize and realize the value of the
vehicle. Of course, the stock suspension sucks. And there are limited
alternatives.
KYB is not an option. While they are arguably somewhat better for the
rear than the completely stock set up , you can only get them for the
rear...and they are poorly matched to the front Boges. The result is an
improvement so insignificant and with drawbacks that it does not really
qualify as an improvement.
The KYB lack good dampening, but offer some measure of stiffness the
stock set up lacks. The stock Boges offer decent dampening, but overall
everything is a little too soft. Not much you can do about the KYB
dampening. You can, however, firm up the boges and still take advantage
of their "better than the KYB" dampening. Plus, the Boges are much
better matched to the front Boges than the KYB, and thus work better
with the front. (The KYB and Boges are the only shocks available in the
U.S. for the syncro rear...only Boges are available for the syncro
front.)
The suspension basically has three components. Compression dampening,
when the shock is being compressed; upswing dampening (I think there's a
better term), when the shock is extending; and spring rate. Further
adjustments can be had by adjusting the amount of oil and the pressure
of the gas/air, if any. You can also change the size of the valves
that control the flow of oil and improve the efficiency of the other
components. These are not options on any syncro shocks available in the
us, however. Nevertheless, if money were no object, the syncro could
be outfitted with killer suspension that would vastly improve all that
the vehicle can deliver above and beyond just about any other
modification you could do.
On off road racing bikes, you can (must) adjust both the compression and
upswing dampening as well as the spring rate of both the front and rear
suspension, with the goal being that front and rear work together and
independently. Mosr experts also have the shock custom valved for their
weight and riding style. The factory suspension for the top
professionals is vastly ahead in performance of anything available to
everyone else. The only way to obtain the right set up, though, is to
test and test and test. There are general rules to follow.
The suspension should be firm yet supple and responsive. To achieve
this goal, you have to have the right spring rate and dampening, which
must work together. Since there's not much to be done with the
dampening on the shocks available to us, all we are left with is tuning
the spring rate.
On off-road racing bikes, the spring adjustment is referred to as "sag
height." This is the amount the suspension sags when fully loaded.
First you measure the suspension unloaded. Then you measure the
suspension (the amount of compression) with the rider sitting on the
bike. You adjust the "pre-load" of the spring until the difference
between unloaded and loaded "sag" is within pre-determined specs. The
pre-load, or spring rate, adjustment is accomplished by turning a large
nut which can be tightened to compress the shock spring or loosened to
de-compres it. The same adjustment can be had by inserting a spacer
between the spring and the shock body, thereby further compressing the
spring even when the bike is unloaded.
There is an optimal "sag height" for the syncro. No one has figured it
out yet, at least that we know of. Ideally, we would start with a
bilstien shocks with adjustable dampening and an adjustable spring rate,
and then do a lot of testing to figure out the best settings for both
dasmpening and spring rate. All we can do with what's available,
though, is adjust spring rate to the best available and
front-rear-matched dampening, which happens to be the stock Boges.
Derek Drew introduced me to the concept of using stock spacers
used in the rear suspension to pre-load the rear springs. Derek added
three spacers or donuts to each of his rear springs. His goal was to
raise the height of the vehicle (ground clearance). From my dirt bike
experience, I deduced that what he was doing was reducing the "sag
height" of his syncro. Yes, this raised the clearance of the
vehicle...but it did so by increasing spring rate, so that at every
level of compression, the spring was stiffer, and hence the vehicle sat
higher, than before he inserted the three spacers.
If ground clearance is your only objective, then insert as many spacers
as necessary to cause your suspension to be fully unloaded even when
fully loaded, i.e., no "sag height." If you also wanted want your
suspension to perform optimaly, however, you would not do this. If the
springs are too stiff, they will inhibit the shock absorber's dampening
action, on both the compression and upswing strokes. The result will be
un-responsive compression dampening and bouncing up-swing dampening.
This makes for a pounding and abusive ride. Even at low speeds, it
unduly streesses other components. Your traction will also suffer
appreciably in the wet/mud and the snow, and over fast rough stuff.
My guess and experience suggest that the best shocks to use are the
stock Boges, front and rear. I have not done any testing to determine
the number of spacers or donuts to insert to obtain the optimum spring
rate. thus far, I have inserted one on top of each rear spring. this
set up is definitely better, IMHO, than the KYBs. The stiffer
spring-rate adds firmness without sacraficing dampening. One spacer on
top of each spring gets rid of the rocking and rolling, and provides a
more stable ride, but it still allows the dampening of the Boges to
abosrb bumps, without bouncing back too quickly on the up-swing stroke.
For me, I am guessing that a spacer the size of the stock donut on the
left front and rear, with a slightly thinner spacer on the right front
and rear would be pretty close to optimum or a good starting point.
Only through testing can you know for sure. Ideally, we would all get
together and have someone build us each a set of shocks with adjustable
dampening. This is more feasible than you may realize. Untill then,
all we can do is play around with those spacers and see what we can come
up with.
steve
1990 syncro westfalia
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