Date:         Wed, 1 Jul 1998 08:26:18 -0600
Reply-To:     Fred Porter <fporter@EYRING.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Fred Porter <fporter@EYRING.COM>
Organization: EYRING, Corp.
Subject:      Re: spacers and sproings
Comments: To: vanagon@vanagon.com
Content-Type: text/plain; charset=us-ascii

> If it can be done to a motorcycle, why not to each wheel on a car?  Truth is
> that it is in some applications...no reason why it can't be done here.
> Pre-load is no different than inserting a stiffer spring...it is stiffer
> throughout the range of travel.

***you obviously don't understand springs or are using 'stiffer' the
wrong way.  Preload only increases the force the spring pushes back by a
constant amount through the range of travel.  If the spring has no
preload and the mechanism the spring is in is extended all the way--your
motorcycle with no one sitting on it and no turns on the adjuster knob,
or the rear of the van jacked up, wheels off the ground--the spring is
neutral, exerting no push or is extended all the way.  Inserting spacers
or adding turns on the adjuster knob only means that when the mechanism
the spring is a part of is extended all the way, the spring will still
be compressed some and exerting 'push' forces.  Conversely, if you
stretched the spring (elastically) and extended the mechanism the spring
would be exertind 'pull' force.

The stiffness of a spring is a physical characteristic of the spring
that you won't change by stretching or compressing the spring within its
elastic range of use (all else being equal).  Now if you stretch the
spring to the point where you actually bend the coils, i think that
would make the spring 'stiffer'.  Take apart your ball point pen and
play with that spring a bit.

Don't confuse the amount of force you get from the spring at various
points through its travel and stiffness...they are two TOTALLY different
things.  And don't do rediculous thought experiments like inserting 12
inches of spacers cause that isn't a realistic application--you'd bend
something.
>
> If Harold's spring's are not stiffer, why does it handle better in turns and
> not roll so much anymore.  Sag adjustment is supposed to do exactly what
> Harry did.

Because you're just preloading the spring and it will take more force
to  get the same initial compression and overcome the preload.  youwill
still get the same amount of spring compression for a given force
however.
>
> Anyway...seems like this will never be resolved through debate....I already
> pissed derek off and probably others, too.

***Right, cause i think some fundamental understanding of springs is not
present.
>
> I know from 25 years of tuning suspension on bikes that I am right.  That's
> good enough for me.  :~)

That's like saying that my 13 years of driving with a clean record means
i know the motor vehicle laws.  Not really, it just means i haven't got
caught.  I think your 25 years of experience has given you a well tuned
tush, but i don't think it necessarily means you understand springs in
interms of the spring response, stiffness and preload
(math/engineering).  You know how to adjust things to get the ride you
like.  But isn't the tush factor what's important as long as you aren't
compromising safety or reliability?

i really think that from the content in the thread at least Larry and
Steve would benefit by getting a book from the library about springs,
not a web site from yamaha or whatever, but something about springs that
explains forces, stiffness (spring constants), preload, and spring
response.  Just statics will do.  You guys throw around preload,
stiffness, travel and force interchangeably in your thot experiments and
they aren't interchangeable--they are unique quantities with their own
definitions.

later,
fred




> steve
>
> Fred Porter wrote:
>
> > That does it!  Can't you guys (Larry and Steve) see that what Larry says
> > below totally supports the non-preload contingent of the list (which is
> > almost everyone except larry and steve).  By tightening the knurled
> > spring adjuster up a little (see Larry's caveat of _with nobody on the
> > bike_ ie. suspension is topped out and the spring is constrained) you
> > effectively insert a spacer.  Then when you sit on the bike, loading it,
> > the sag is less and the rider rides a bit higher.  There are two very
> > different conditions being mixed up here:  loaded with sag and
> > unloaded/topped out.
> > The preload is increased ON THE BIKE when unlaoded and topped out and
> > you tighten the adjuster.  Once you load the system (van or bike) you
> > are changing the ride height.
> > Preload is only effected when you have a constrained spring in the case
> > of the UNLOADED and TOPPED out suspension.
> >
> > > Motorbike tension adjusters are similar in their effect.
> > > With nobody sitting on the bike, the spring might be extended all the
> > > way, limit of travel. (On a vanagon that almost never happens)
> > > Now you tighten the adjuster and you compress the spring, but not
> > > raising the height of the bike, but just increasing the tension on the
> > > spring. (with nobody on the bike)
> > > Once you get back on, the bike will of course sag less, since the
> > > springs are now more stiff. ?????
> >
> > the spring is NOT more stiff, you've just raised the position of the
> > lower perch.
> >
> > > Does this mean a vanagon is like a motorbike with someone big
> > > sitting on it ????  imho
> >
> > if you put someone big on your bike it would sag more for the same
> > spring adjuster setting.
> >
> > so the westy isn't leaning, that was fixed that by increasing the ride
> > height of that side by raising it with a spacer at one end of the spring
> > not by making the spring any stiffer.  I wouldn't go sticking any
> > spacers inbetween the coils as that will limit your useable travel.
> > Spacers inbetween the coils will make the spring stiffer and if you use
> > Larry's method of thinking about unreasonable extremes then with spacers
> > inbetween each coil it will no longer be acting like a spring, but like
> > a solid rod REALLY stiff--no suspension at all.  You guys could do
> > that--just remove all the suspension components and put screw jacks in
> > there and load level all day long :)
> >
> > later,
> > fred