[Torbjorn968]

I read an interresting article the other day stating that damper rebound can be used with a simmilar function to sway bars. The advantage of using damper settings was that they allow you to vary the relative grip between front an rear from turn in until the moment you hit the throttle again.



I understand it like this: if the dampers up front have a softer rebound setting than the rear the front tires will stay planted to the tarmac during turn in while the harder rebound setting at the rear will reduce grip on the inner rear wheel allowing the tail swinging out. With correct settings the rear inner wheel can be made to make more and more contact as rear grip is needed on exit.



This may imply that my ambition to use 255s around the car is wrong: on exit the demand for grip at the rear will be more than at the front even assuming 50/50 weight distribution since the rear will take care of both side grip and accelleration.



With wider tires at the rear you could first reduce the grip of these and hence counter understeer tendencies on turn in as described above, then, when needed, the rear innerwheel would increase its contact and you would get an appropriate distribution of rubber areas against the tarmac on exit: more rubber at the rear.



There are however practical advantages of 255s all around both in terms of economy and as a practical issue bringing spares to the track. The question then is if you can achieve a simmilar effect to the ideal scenario above: reducing the grip in the inner front on exit to create neutrality under accelleration. A stiffer front sway bar does the work in static terms: lifting the front inner wheel. The question is how this works during turn in?



Hypothesis:



A softer rebound setting at the front will allow the coils at the front to fight a stiffer forward swaybar and increase forward contact area on turn in. As the rear inner wheel is pushed towards the tarmac at a slower rebound rate roll will increase and the stiff forward swaybar will do its job and start to lift the inner forward wheel.



Since the rebound rate shoud be time dependent using damper setting should create a car which is understeery in long fast sweepers (the difference in damper rates cannot hold oversteer interminably). But this might be what is wished for?



Another issue is the use of a rear wing. The addition of grip is dependent of speed. Does this coincide with different wishes for dynamics in slow and fast corners?



//TL

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[Eric_K]

The dampers don't influence the balance a great deal under steady state cornering, but do influence the entry and exit behavior. Your springs/sway bars will mostly determine the mid corner balance, the dampers will mostly effect the transitions. I think you are implying you want entry oversteer and exit understeer? I might try reducing front compression and increasing front rebound. I think this would transfer more weight to the front on turn in and shift it quicker to the rear when exiting.



Now that I have adjustable shocks, I have found this cheat sheet to be handy. It is for a Ford Mustang series but the shock tuning is applicable to any 2-way adjustable. See page 5. http://www.fordracingparts.com/mustang/fr5...e_FR500S_v1.pdf



My thoughts on tires sizes are to get the widest you can physically fit, somewhat regardless of front/rear ratio. Then you have the maximum tire grip available, then tune the suspension/balance to the grip you have available.

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[Torbjorn968]

I have LEDA suspension with one knob to adjust and I guess this is rebound adjustment.



Thanks for the FORD guide! Fits with what I wrote (I think.....?)



//T

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[flash]

while adjustments can fake you into thinking the car is doing something better, it could actually be going slower - i wouldn't rush into making big changes without first taking measurements of entry and exit speeds



all of the adjustments though presume that the car isn't fighting you - if the chassis is allowing geometry change, you could be masking one symptom by creating another - same goes for body roll, weight transfer, and spring rates



the first thing to do, if you want to do it right, is graph the car - this requires some precise measuring equipment to take readings of weight transfer, and suspension geometry change



if you don't have that equipment, then you can do a lot of it with cameras strategically placed both in the car and on the track - looking at how the car is balanced at different points will tell you a lot



one quick thing that tell you there are chassis, geometry, or spring issues, are if you have the inside front tire in the air - that should never happen - you should never have less than 50% contact patch on that tire - if you do, you have things to work out



something else to remember is that shocks are only there to slow down and control the frequency of the spring - over thinking what they are doing, or over taxing what they are there for, can really get you into uncontrollable situations, and almost always results in slower exits

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[Torbjorn968]

Thinking of this as one more adjustment which I have not understood the impact of before. So a bit here and there.... With the aft sway bar in mid position the car now has too much mid corner oversteer with same size tires around to the point that you as a driver at times becomes rather long faced when the rear end comes about. Happened to both my self and my Endurance team mate who borrowed the car.



So as a first step. Softest arb setting at the rear together with an adjustment in the relationship of damper settings fore and aft. Then when I have a new reference: stiffer sway bar front.



//TL

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[flash]

given how stiff your springs are, i suspect the problem is chassis flex and not damper settings - what are the tubes like in the rear of the cage?



the other thing to look at is what the contact patch area is on the inside rear tire in a corner - if it is in the air, corrections in the setup need to be made to bring that tire back down



this is all the nature of a unibody car - load is transferred across the car, and consequently it is very easy to upset the limited balance and weight transfer capabilities, which are the key to fast exits - while a unibody car generally initially handles better than a framed or tubed car, there is a limit to how much load it can transfer - many people try to solve this by over-springing or adding too much negative camber (i've done it myself) - this results in a twitchy car that will both oversteer and understeer, and often at unpredictable or undesireable times - unfortunately the solution involves adding weight in tubing in some generally difficult places



but, how cool is it that you get to play like this?

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[Torbjorn968]

[quote name='flash' post='56628' date='Jul 23 2008, 04:30 PM']given how stiff your springs are, i suspect the problem is chassis flex and not damper settings - what are the tubes like in the rear of the cage?[/quote]



The cage is a 944 Turbo Cup item. This is a full cage with a diagonal behind the seats, also twin longitudal struts to the rear of the car and a diagonal one. I generally leave the diagonal out in order to get all the gear in the car. But perhaps I should get back to the habbit of bolting it in after unloading...



//TL

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[flash]

yup - in fact, in a good design, there should be one that goes across to the lower point of the frame in the rear, through the rear bed panel, all the way to the top of the main hoop, crossing the car in an "X"

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