[flash]

actually i do agree with that - sway bars are last in hardware installation

the first step is to tie the chassis down - reinforcing the suspension mounting points so that they don't move and cause camber undue change is the first thing i do - the front lower ones on the 968 are particularly soft

then i spring the car to the point where balance is achieved and the natural weight transfer is set to where i want it

then i dampen the car to achieve the spring frequency i am looking for, carefully balancing compression against rebound, and steering clear of anything gas charged for street, especially in the rear

then i add the sway bars to flatten out the car and transfer more weight to the inside tires

then i re-tune the dampening

once i braced the lower mounting points, i found i was able to reduce the negative camber and gain inboard tire contact - then i found that there was still more roll than i wanted - i then designed my bars and immediately the car flattened out - i am now able to reduce even more of the negative camber

as you say, there can be a point of "too flat" - there can also be a point of "too stiff" for both the suspension and the chassis - a certain amount of flex can be good - it is also very easy and an incredibly common practice to overspring a car - weight transfer is a complicated issue, requiring a LOT of math and a lot more testing under controlled conditions - you really need to rent a track and a skidpad for a day to work it out - it really can't be done in a DE or something like that where you can't repeat speeds and such accurately enough - it's better than nothing, but doesn't come close to the ability of a track to yourself - i'll be doing that again in the next few weeks - it's a lot cheaper than you might think too

as for my spring rates, i am currently running 300# up front on hydraulic dual adjustable konis and 500# in the rear (no torsions) on modified hydraulic dual adjustable carreras - remember, this is a street car - i had 400/600 in there, but it was just a bit much for the street - on a dedicated track car i would probably be in the 500/750 range, but maybe not quite that high - it would depend on the weight of the car - the one we are planning will be about 2200lbs, so 400/600 is likely more like it

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[333pg333]

Well that sounds a comprehensive way to do it. When you say brace the lower mounting points, you're referring to an actual brace, not just replacing rubber bushings / bearings? Is this something akin to the Brey Kraus brace?

Interesting how you've reduced neg by a lot. So you don't have the tramlining effect so much but good turn in.

I'd love to do the full data test acquisition session with gyro sensors, working with suspension setup, tyre temps and pressures. corner weighting, aero etc all in a day. I'm sure if you have enough money someone would provide that service.

Did you do anything to brace your upper mounting points in the rear with the T B removal?

2200lbs is very light. This is a 968 based project I take it? That's lots of c/f panels I'm thinking. I think springs would be very interesting on such a light car. I know of 951/968 cars that have gone up to 1200lb springs but it's very subjective too. If I press the 'GO' button on my trackcar project I want to change the rear suspension setup completely to something more modern. Perhaps a Corvette or 996 rear end...all for the future...

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[flash]

i am referring to a brace similar to the brey krause - those lower points move a LOT, and result in a major amount of camber change

the only remaining tramlining is due to my tire choice - that will soon change - turn in is excellent

you don't need a lot of money - you can use commonly available tools like a g-tech, dynolicios software, and things like that, to determine what is going on - all you really need is a track that is not populated with people trying to pass each other, so that you can get consistent readings

the rear has polybronze bushings in the torsion tube, and spherical bearings on the inner points - the upper point is stock

the track car will indeed be a 968 - it will be a cab though, and lain out in speedster fashion - no windshield - no windows - dash pod only - use specific wiring harness - mostly fiberglass body - sealed doors - carbon fiber torque tube - aluminum torsion replacement, yada yada - powered by a supercharged engine - should be fun

lol - now all i need is the time and space to do it

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[Lonestar968]

I remember always reading how our cars were always touted as having an almost 6th sense when it came to cornering, much akin to the 928's and such writings were typically underscored with words about Weissach and such.

So with regards to turn-in, flex and geometry (camber, etc) changes under hard lateral loads, how much do our chassis suffer when they are well braced as mentioned above? Or do the bracing benefits outweigh any negative handling properties? It sounds like bracing is definately the way to go but I'm certainly no expert.

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[flash]

there is definitely such a thing as "too stiff" when it comes to a chassis, especially in a unibody like ours, but bracing these cars as we are doing now has resulted in nothing but positive effects

it really goes to how compliant you want the ride - the stiffer you make things, the more you feel things, but the better the car handles (assuming you don't go too nuts and brace every spot on the car)

the factory set it up the way they did for a number of reasons, not the least of which was choosing an economical compromise between performance and cost

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[333pg333]

Lonestar, there really is a line in the sand somewhere, but it's up to you to draw it. Thing is, many will change where this line lies due to adding more and more performance upgrades. There's a slight advantage in having a n/a car in that you can't get instant big power hikes like a forced induction version, so it helps to keep that line stable for longer. Many people start to make their road cars into track day weapons, but this is really not the way to do it. It will always be a compromise. If you are strong willed and happy to either compete in the one class with your buddies, or just have a nice road car, then you can make a few changes and get off the merry go round. Otherwise, I would suggest stopping and re assessing before you sit atop that long steep slide and take the plunge. You'll notice that it's very hard to stop once you push off.

Putting a roll cage in can be a very effective way of bracing your car of course.

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[bob blackwell]

Lonestar968, this week-end at the track in Arroyo Seco you will have the opportunity to compare my moderately stiffened 968 with your stock suspension and see what you think. For a daily driver with occasional track use, I think I have reached a good compromise. If I wanted to run wheel-to-wheel races competitively, I would make it a lot stiffer. Looking forward to Saturday! Good luck, Bob Blackwell.

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[craigawoodman]

I run 235/40R18's on the front with 21mm spacers (off a GT3) and they just touch the inner wheel plastic on lock. I run heaps of negative camber with camber plates and castor to get them in the guards.

On the rear, I currently run 285/35R18 Dumlop Dizzera D03 track tyres. These just hit the guards with 21mm spacers fitted. This is also with a fair bit of negative camber dialed into the rear to get them inside the rear guard profile.

According the the Performance Box - I can pull up to 1.35G lateral on the track. This is not constant, but peak.

So if I can fit 285's (I think they are on 10" rims) with an additional 21mm spacer to move the rim out to the guard, then an 11" is possible.

Regards,

Craig

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[333pg333]

Craig, just ot for a minute. What other R spec tyres have you tried and what is your opinion of the D03's?

I have used R888s and RE55s. I'd like to try something else but I don't know anyone who has used the Dunlops. They seem to have a pretty good reputation.

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[craigawoodman]

I was using Pirelli track tyres before the Dunlops. The Dunlops have heaps more grip - around 1 sec plus per lap - but they wear much quicker (that is the trade-off).

I have just fitted the third front tyre and need to replace the non-working side. I have done two working side rears for one non-working side. So having only clockwise tracks does not help. So over a season of around 12 track days plus a hill climb and a little bit of driving I have gone through one front and rear on the working side (they have done two events also this season) and have just fitted a new rear (two events) and fitted the third front working side half way through the second event of this year).

Short answer - expensive but very grippy. I am running the mid compound rather than hards.

I got moved up a class this year and can now run the Hoosier semi-slick without penalty. These are supposedly road legal (how can a slick with two grooves be legal) and provide more grip and supposedly wear better.

The problem is that the Hoosier will be absolutely hopeless in anything other than dry track situations. The Dunlops work well in wet and dry situations.

I was chasing a GT3 Cup car around Lakeside on the weekend with two people in it and probably going slightly faster (but did not want to mix paint).

I am happy with them (the fronts cost around $600 and the rear are around $700 each AUD). I tried running them at the recommended 28psi and they were a bit squirrelly - so I will try around 30 psi next event (I used to run 32psi but am told this is too high).

Hope that this helps.

Craig

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[333pg333]

Hey that's good info thanks Craig. I have run R888s, Hoosiers (both R6 and A6), and Bridgestone RE55s. Obviously the Hoosiers are the best however we get immediately thrown into Open class with Cup Cars and 600hp lightened GT2's etc so it's a bit hopeless. Next season will see me compete against those guys but not for now. So I've decided to drop back to A class which means back to R spec tyres. I have found a cheap place to get some 275x 18 Nitto NT01s which a lot of people seem to like. That's the widest they make in 18" except for 315s which I can't fit so I'm stuck with them. Having said that, running a square setup is advantageous in a couple of respects. I could run the Dunlops in 285/295 but as you say, the cost is prohibitive. At $700 per tyre vs these Nittos for about that per 2 tyres, it becomes a hard decision. Probably means a second at Eastern Creek but a much lighter back pocket, so....

Anyway I'm sure you can fit 11"s out back on your car, but as has been mentioned, it really comes down to suspension, ride height, offset, camber, and even brand of tyre. Some are much wider than others. I've had 295 Hoos on my 10"s and there is room to spare. The only thing I would advise you is that you should increase your fronts at the same time. You really don't want that much of a stagger on our front engined cars. Bear in mind that there are guys running 315's all round on modified 951/968s in the US so square (or close to it) is proven to be better.

Hmm...now you've got me thinking about increasing my Simmons to 11"....

Oh, and those are very low pressures if you mean hot?? How much does your car weigh and is it modified much?

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