[flash]

they don't make springs soft enough to do a dual spring setup on the rear, if you plan to keep the torsions.

 

the good news is that you don't need to do that.  because you have torsions, you essentially already have the first spring.  all you need is a helper, coupler and tender.

 

so, yes, i have a setup worked out.  if you have about $4k to spend, anybody can have it.  putting the list up on the site is on my "to do" list

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[PorscheG96]

Sam, I have a model that can give you several ideas.  PM me.

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[PorscheG96]

they don't make springs soft enough to do a dual spring setup on the rear, if you plan to keep the torsions.

 

the good news is that you don't need to do that.  because you have torsions, you essentially already have the first spring.  all you need is a helper, coupler and tender.

 

so, yes, i have a setup worked out.  if you have about $4k to spend, anybody can have it.  putting the list up on the site is on my "to do" list

 

I recently designed a dual spring setup both front and rear + kept my torsion bars.  It's totally kickass and was at least 1 second faster at autocross without even corner balancing yet and I had a couple other unrelated setup issues.  Torsion bar doesn't act in series with the coils so you don't already 'have the first spring.'  But I'd probably agree that it doesn't make sense to do stacked springs unless the main is really stiff, and for street driven 968's this doesn't really make sense.

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[flash]

actually, it depends on how the second spring is set, and when you have it come into play, as well as the valving you choose on the shocks.  it won't be as progressive as a true dual spring, but it will still be progressive as the rate of compression changes as the spring loads up in its motion, and the shock come into play.  it's complicated, and i'd need charts and an easel to explain, but it works.

 

the problem is product availability.  for autocross, you spring light so you get lots of initial roll.  slightly stiffer than that for street, and stiff only for track.  since the lightest tender for a stacked setup is 150, if you add in the 175# of the torsions, by the time you get to the front, you would end up too stiff in the front for either street for most people, and definitely too stiff for autocross.  that leaves on a standard spring.  90# is the lightest i've found.  that matches to a 250# final rate up front, which isn't too stiff for street.  if you stack tenders up to get a lighter rate, you have a lot of moving parts that tend to make a racket, and again not a good match for a street car.

 

all of the magic though is in not using gas shocks and struts, and sticking with dual adjustable hydraulics.

 

side note:  g96 - i bet i could make your car faster for autocross, but we'd likely have to remove most of your stuff, and you wouldn't want to drive it on the street anymore, as it would be a rolley polley loose feeling car.  we could talk about that though.  i've thought about setting one up for that, but autocross bores the crap out of me, and i'd probably not be happy dealing with it, unless i had somebody else drive.  that's why i quit driving that a long time ago, and just set cars up, almost all of which won.  it would be fun again though to see the looks on the faces of those kids who are setting their cars up like track cars, and thinking they are building a fast autocross car.  did it before.  great giggles.

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[bill3]

Flash,

 

If you've posted this info elsewhere, please point me to it. I take you at your word about "soft for AX, stiff for track" but I'd like to understand the logic/physics better. I'm assuming the stiff part has to do with minimizing weight transfer and keeping grip on the inside wheels, but I could be wrong.  I'm also interested in your comment about "over lowering"; I know lower cg is always good but the tradeoff is a lower roll center; I'm just not sure how all of that interacts. 

 

On the shock issue: I have M030 yellow Koni's on front (which I think are hydraulic but not sure) [with what were described years ago as "variable rate turbo cup springs] and Ledas with 150# helpers and stock (not M030) torsion bar on the back. Car is lowered to what I believe is very close to European ride height, perhaps a bit lower. It handles well as a dual purpose street/track car from what I can tell but I'm always trying to learn more

 

Many thanks!

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[EEZATOY]

Flash,

 

Look forward to seeing your list...My car is getting ready to hit 100K and I'm looking to freshen it up a bit...

What shocks are you currently running?

 

Thx Sam

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[flash]

bill - in autocross, unlike on the track, weight transfer is everything.  you don't want the car to be as flat in the corner.  you need the weight to move around.  on the track, you are trying to keep the weight a lot more evenly distributed.  on many autocross cars, i, like many, actually disconnected the front swaybar.  it's all about getting the rear to plant and grunt out of the corner.

 

M030 shocks and struts are gas.

 

torsion bars are the same on M030 cars as on standard cars

 

lowering to a point where the geometrical roll center goes below ground creates too much camber change and reduces net contact patch area, which costs time in the corners.  so does setting too much negative camber.  a lot of guys make that mistake.  you can go down about an inch on these cars without getting into trouble.  much more than that and it starts costing.

 

that being said, what you have now is a pretty decent setup for street and non-competitive track.  i am not a fan of the M030 valving, as the gas preload tends to make the car jittery, especially in the rear.  it would be limited in autocross, and you would find yourself fighting the setup.

 

you would be amazed at how many people do it wrong.  it's as if they are all following the same book or something.  i don't think many of the guys out there actually understand the physics.  even more think that because a guy is winning that it's the car.  some guys can just plain drive, and they would win in a shopping cart.  other guys couldn't win no matter what car they had.  in autocross, it's not the car, it's the driver.

 

eez - i'm running modified and re-valved qa-1 double adjustable hydraulic shocks in the rear and koni double adjustable hydraulic struts up front.  the shocks are about $250 each, plus mounts and bearings.  all in you get close to $800 before adding springs.  the struts are about $700 each, and again you then add springs.

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[bill3]

Flash,

 

thanks for the info. The few times I've run Autocross lately, I've stiffened the rear roll bar (adjustable); disconnecting the front one is an interesting alternative!

 

I knew that getting the roll center too low was a bad thing but somehow I've never quite gotten the physics of what it does to weight transfer and camber change. Makes sense that too much camber change is a very bad thing.

 

I do find my front combination of shock/springs a bit "bouncy" on the road but never an issue on the track; almost as if the shock is overpowered by the spring. But it's not unpleasant and works fine on the track (as long as I tighten the top adjuster at least 1 turn) so I haven't worried about it.

 

Sounds like if I really wanted to get the "right" shock setup, it would cost some serious $ (including the black magic of figuring out how to adjust the double adjustable shocks!)

 

thanks again!

 

Bill

 

PS I have Leda shocks on the back; not sure whether they are gas or hydraulic; not adjustable. I need to do some more research about them

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