[DeTomaso] need formula for springs needed-- was shocks for ORR

[David & Marilyn Bell]

As a point of reference, I'm running 400# front and 650# rear springs on
Aldan double adjustable shocks.  The rear shock compression knob is set two
notches stiffer than midpoint, rebound is one position softer than midpoint.
The front shocks are set at one notch stiffer than midpoint on compression,
one less than midpoint on rebound.  Street tires, which I also use for ORR,
are 245/35-17 front and 295/35-18 rear.  The street ride is firm but
definitely nowhere near jarring (Marilyn doesn't even complain when she
passengers with me as long as the AC is working).  The ORR handling (Big
Bend only so far) is slot-car flat, neutral (no noticeable under or
oversteer) and very predictable.  But I haven't been over 124 mph (my max
tech speed) on the Big Bend course either, and BBORR doesn't have the big
dips that Mad Dawg has encountered at higher speeds elsewhere.

My track reference for shocks/springs is TWS, where the Turn #1 transition
from steep 8 degree banking down onto the flat infield section is both
severe and very fast (~ 150mph).  The suspension really gets slammed there
and if the car gets unsettled, it's very easy to exit the track at an
extremely high rate of speed.  The same Aldan shock/spring settings handle
the pounding very cleanly with no suspension bottoming and no tire/fender
body contact.  I do run 225/45-15 front and 275/50-15 rear Hoosier slicks at
the track vs. the 17/18 ORR combination.  Track handling is perhaps not
quite as flat with a little more sidewall flex, but the still very neutral
and predictable, and the slicks are much stickier.  I suspect that the
taller sidewalls of the 15-inch diameter track tires provide a little extra
spring cushion over the 17/18 ORR tires that help out coming off the TWS
banking.

So MD, I'd say your solution is to either go to 15 wheels/tires or seriously
cut back on the jelly donuts.  Since there isn't much in the way of 15 inch
ORR rubber available, the choice seems pretty clear.

I hear that Jenny Craig has some openings for fat-pill slackers.


Muscat Dave Bell (now driving a 4-WD in the desert instead of a Pantera at
the track)



H





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>>>>

Nice work Jim. I like your analysis here. I'm pretty sure my springs
are 750lb and 450lb rear, front respectively. Its the setup that Bobby
at Precision Proformance recommended. that extra 50lb may be enough to
keep Dennis's booty off the road :)

On 10/10/07, Mad Dog Antenucci <teampantera at yahoo.com> wrote:
> Fellow Slacker! ;-]>
>
> I think you, Jason and others are all right on with your spring concern
> comments.....all the supporting feedback from mfg's and unlimited drivers
is
> forget replacing the shocks and just make an incremental increase to the
> springs to the back end where I had a problem or full compression.  I
> currently am running 400 lb fronts and 700 lb rears.....I may have to
> consider raising the back end up a half inch or so too but hate doing that
> since the car handles so well at every other ORR and at speed be it in
> straights or corners of canyon road I am reluctant to make big changes.
>
> I'm not sure what my speed was at when I hit the first dips but its at the
> end of a long straight...I could  have been 150 but was probably closer to
> 160......so right now I am going with a 750 on rears and adding a poly
shaft
> stop on top shock shaft for added protection....if that doesn't work I
will
> give up the donuts, macaroons and beer. ;-]>
>
> thanks for your comments.
>
> Dawg
>
> pantdino at aol.com wrote:
>
> Dennis and Jason,
>
> I freely admit that my opinion comes from a total slacker regarding ORR,
but
> I wonder if stiffer shocks is the right way to go. My understanding is
that
> it is not the shock's job to prevent excessive spring compression-- if
that
> is happening, the spring is too soft. The shock's job is to dampen the
> spring's natural tendency to continue to let the car bounce up and down
once
> it is disturbed. Indeed, the Brits call them "dampers" because that's what
> they actually do.
>
> At the risk of boring you to tears, I had an Alfa that was "undersprung",
> that is, the springs were too soft.? Despite Konis set on full hard so
> expansion joints rattled my teeth, the car would still "porpoise" when
going
> thru depressions at intersections for water to drain away. The car was
> "undersprung and overdamped."? In contrast, my MGB was "oversprung and
> underdamped".? It would also rattle my teeth over expansion joints but
never
> porpoised. However, the ride was "bouncy," where you could feel the car
> oscillating up and down more than it should after hitting a bump.? So its
> dampers were not preventing the car from bouncing along in its springs.
>
> What spring rates are you and Jason running??? I have no real world
> experience at this, but if Jason doesn't bottom out at 150mph, that gives
> you an idea of what spring rate is necessary to contain a certain amount
of
> kinetic energy. Basically a car encountering a change in road shape is
being
> forced to change its course from straight ahead in the vertical plane to a
> different trajectory. Inertia wants to keep it going straight, and the
> springs have to transmit force to prevent it from burrowing into the
> asphalt.?
>
> It seems to me that since Kinetic Energy=1/2 Mass x? (V squared), you
could
> get an idea of what spring force would be necessary to keep the same mass
> from bottoming at a different speed.? I'm afraid my physics is too rusty
to
> give you the formula, but spring strength is measured in pounds, which is
a
> measure of force, mass x acceleration.? The springs have to accelerate the
> car away from the road. If they are not strong enough, they bottom out and
> the whole car becomes unsprung weight. So the spring has to have enough
> strength to not bottom out under this extreme load.?
>
> Again, I don't have the equations for you, but I suspect everything will
> drop out of the them and you'll be left with the velocity squared factor--
> if the car is going twice as fast the springs will have to be 4 times as
> firm to prevent bottoming.?
>
> Meaning you'd be looking at something like:
>
> Jason's spring rate x??? Dennis' speed squared
>
>
> ?????????????????????????? Jason's speed squared??? =? spring rate needed
to
> prevent Jason's car from bottoming at Dennis' speed.? If Dennis' car
weights
> more or less than Jason's, you would correct by a simple proportion, as
the
> M is not squared in the formula.
>
> However, I think this also assumes that the springs in the two cars are
the
> same length and will crush the same distance before they bind, etc, etc.
But
> it should provide a ballpark estimate, I would think.?
>
> Jack and the other people who really know and don't just make slacker
> guesses like me??
>
>
> Jim Oddie
>


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