[Torbjorn968]

With racing type suspension the MO 30 swaybars seems to soft. Have looked at the Elephant racing items. Any other proposals?



//TL

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[flash]

lol - yeah, but you need to do lower chassis bracing first, especially down below - stiff swaybars make for some serious ripping of the sheet metal they call a "frame", unless you do the job of really reinforcing that area



currently i am running 31.75mm front and 22.25mm rear

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[Torbjorn968]

Lower chassis bracing, is this a concensus in the states? Sorry for being a sceptic but I have gotten the reverse opinion here: that it will not accomplish much. It would be interresting to have the input from other racers on this.



//TL

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[flash]

lol - i get that from a lot of people UNTIL they drive the car with one in there - you can feel the difference, even on a hardtop car

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[Torbjorn968]

I bought the Tarret Engineering items. Interrested in how to set them up. With the MO30 items I would suspect that I end up with the minimum setting (i.e soft) at the rear with 255s all around.



//TL

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[flash]

it all depends on what you have done to the chassis - if you haven't reinforced the lower sections, then set them as light as you can - then drive the car and measure your exit speeds and camber change, as well as body roll angles



by the way, this all presumes that you have not lowered the car too far, and dropped the roll center below ground - it's very easy to do - there is such a thing as too low

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[mikew968]

What is the "right"height?



Mike

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[flash]

"right" is subjective



i haven't drawn it out yet to confirm, but it looks like about 630mm fender arch to ground with 25" O.D. tires is the minimum - lower than that and it seems that the roll center goes below ground, which actually scrubs speed in the corners

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[Torbjorn968]

[quote name='flash' post='56770' date='Jul 27 2008, 06:32 AM']"right" is subjective



i haven't drawn it out yet to confirm, but it looks like about 630mm fender arch to ground with 25" O.D. tires is the minimum - lower than that and it seems that the roll center goes below ground, which actually scrubs speed in the corners[/quote]



Will meassure on the fender. I have a about 3" of clearance to the ground at the side skirt. Looking for a starting point for the swaybar settings. The approach flash suggests is great if you have lots of time on the same track and you are an extreemly consisitent driver taking time to analyze Driftbox readings between stints. Looking for something approximately correct to slowly work myselt towards something more approximately correct.....

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[Torbjorn968]

[quote name='Torbjorn968' post='56774' date='Jul 27 2008, 08:30 AM']Will meassure on the fender. I have a about 3" of clearance to the ground at the side skirt. Looking for a starting point for the swaybar settings. The approach flash suggests is great if you have lots of time on the same track and you are an extreemly consisitent driver taking time to analyze Driftbox readings between stints. Looking for something approximately correct to slowly work myselt towards something more approximately correct.....[/quote]



Something like 620 mm in the front an 610 mm at the rear (not quite flat where I was). Will try to get the hold of the chassis engineer who did the intital setup. Any suggestions as to intital sway bar setup?



//TL

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[flash]

nope - no idea where to go there - any suggestion i could make would be one that would mask a larger problem - i'd start as soft as you can



the reason is that your ride height is way below what looks to be maximum drop without changing control arm mounting points and steering rack mounting points - i would not be a bit surprised if your roll center was well below ground - this is not an uncommon mistake a lot of people make with a number of different cars - i've done it myself - it isn't just a 968 thing - it's also easy to fall into the trap



the "theory" prople seem to follow is this: "low is good - lower is better" - they somehow think that the lower the center of gravity the better - that is true to a point - the complication is the roll center - this is not the center of gravity, but rather the pivot point of the suspension at the center of the car - if you have a roll center below ground you can seriously scrub speed in turns and also cause simultaneous understeer and oversteer issues - you have to draw it out to see it, but once you do, it becomes very obvious



i haven't drawn it out yet, but in preliminary tests, it seems that 630 is about the limit before it starts to get "weird" - at anything below that height, the steering rack definitely needs to be relocated - bump steer starts coming in below that, as the angle of the tie rods is no longer optimal - the control arms are also out of position - you never want them higher at the end than at the bushings - that allows for too much camber change as they swing up and down



if you haven't read about this stuff before, there is a really good book out that explains the basics of chassis and suspension setup - it's called "how to make your car handle" by fred puhn - it has some really good explanations and diagrams that point out the concepts



good luck on the swaybars

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[Cloud9...68]

Flash,



I was reading through your lastest post, and am always very impressed with your knowledge of suspension set-ups, and how you seem to be able to apply that knowledge to make a car handle its best. I was going to ask you if there are any books you could recommend that do a good job of explaining this stuff, but then I saw at the end of you post that you recommend Fred Puhn's "How to make your car handle." I read that book years ago, and seem to remember that it was fairly basic, and applied more to very simple, muscle car type suspensions, than to cars like the 968. Are there any other books you'd recommend? Or did you gain most of your knowledge through experience and trial-and-error? Thanks.

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[flash]

while a lot of it was through being around it for so long, some was from college (mechanical engineering) - most though was a result of picking other people's brains over the years (and listening to people a lot smarter than me) - but, there are a few books out there that are a good start on basics



unfortunately i lent out and never got back the one book that i really liked 25 years ago when i had my shop, and for the life of me cannot remember the title or author - someday i'll see it again



how to make your car handle by fred puhn is a basic book, and primarily focused on older cars, but the theories are the same - copywritten in 1981, it does go up through the 70s, which is where our suspension is from - remember the front is a 70 rabbit and the rear is a 68 bug - but, the type of car is not as critical as the ideas behind weight, balance, roll, etc - it's like learning basic math, and then applying it to more complicated situations - once you understand the basics, if you're mechanically inclined, then the rest becomes easy



porsche high performance driving handbook by vic elford has some stuff



automath handbook by john lawler for the geek in you



hope that helps

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[flash]

i forgot to say thanks - i was answering 2 calls and getting ready to get out of here - no excuse though

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[Cloud9...68]

Thanks. I've done a little searching for suspension-specific books, and was surprised by



1) How few of them there appear to be, and



2) How expensive the most highly-rated ones are.



I hate to sound like a cheapskate, but I just shelled out nearly $800 for a pair of ice skates for one of my kids, so price does kinda matter at this juncture of my life.



From following your posts on the subject, it sounds like you've done a ton of testing, which, along with talking to the experts, as you said, is definitely the best way to learn. I'm still at the point in my driving learning curve where the car's set-up matters far less than my technique (or lack of same), but the topic definitely interests me.



And you're right about our cars' suspension being from the '70s; I have a hard time remembering that for some reason.



OK, I'll follow up on your recommendations. Thanks.

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[flash]

most important item to fix in a car's setup is the loose nut behind the wheel

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[Cloud9...68]

[quote name='flash' post='57096' date='Jul 31 2008, 10:51 PM']most important item to fix in a car's setup is the loose nut behind the wheel[/quote]

So true! <img src="/forum/images/smilies/968/laugh.gif" class="smilie" alt="" /> <img src="/forum/images/smilies/968/laugh.gif" class="smilie" alt="" />

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[Torbjorn968]

Have now spoken to the previous owner, one of his mates is one of Swedens top chassis engineers (working for SEAT/Richard Rydell- and 944 Turbo owner to boot). His opinion of ride height was "as low as possible", even lower than the 620 mm at the front and 610 mm at the rear which my car currently rides with. So might be OK, trying to reach the engineer in question personally.



Also spoke to a aquintance racing with the same suspension as on my car (a LEDA kit with damper curves speciefied by same engineer). He had set the Tarrent swaybar at the front to 95% of max stiffness and the rear around 60% and was satisfied with the result.



//TL

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[flash]

i think he's understating the situation - however, what i am saying also presumes that you have done something to correct the very soft front lower suspension frame area - without that, you are masking structural inadequacies and suspension geometry changes, and won't really know what is going on



i see this all the time with a lot of different cars - yes, the car goes faster than if you didn't lower it at all - however, it goes even faster if you correct the geometry and chassis issues



draw it out on paper - you'll see it very clearly



i'm just about to do this very thing, as i work on the suspension design for the next car - i can see that i am already too low at 628mm, and to get anywhere near that point i will need to alter the control arm mounting points to get the control arms level, as well as relocate the steering rack to get the tie rods level - the car lost exit speed as a result too - scrubbing too much off because i have too much negative camber - it also bump steered a lot more, as well as got unsettled more easily



in the meantime, i am raising the car back up a bit - that will reduce some negative camber, get the tires more equally loaded in the corners, as well as get closer to a zero deflection nominal position with the geometry



if you want to go really fast, when setting up a car, you start at the drafting board, not the tool box



good luck

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[968crazy]

measured my car and it sits at about 650mm. It is stock M030 for SCCA but when I had it about an inch lower the car was very loose I raised it and it was much faster and did not snap loose like it did before. A very fast national champion autocrosser is the one that told me the car was too low after he drove it and he was correct. Of course I have no idea how to figure out a roll center but lower wasn't better in my situation.

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