Ok I had a wheel/tyre shop near work take a look at the setup this arvo. (er that's 'this afternoon' in Aussie lingo).

So there were quite a few things out and changes made. The pity is that I don't have a track day scheduled for some time.

They also checked with the bump steer deformation both up and down by hanging 3 or 4 guys off the front of the car. He said that it was quite a minimal change so that was good. Next step is ride height, fix the rear sway bar, and review shock settings.

I want to change out my camber plates. Who uses what? I was heading towards the Racer's Edge ones but reading on their website last night said that they only allow for about 2.5 degrees? http://tiny.cc/v9bjc
This seems pretty weird to me. I know Karl is very experienced in matters front engined Porsche...but I have felt from a couple emails with him that he looks at the old Cup Cars for reference when setting up. Clearly, as evidenced in this thread alone by Dubai, people have progressed from front springs in the mid 300lbs. Perhaps I'm imagining this but the bottom line is that I want a camber plate that gives me the ability for quite a bit more neg than 2.5o. Any ideas?
They have to be the ones that sit up like the RE's, not like my KWs that sit flush. It means that I can lower the ride height without compromising my free travel any.

My idea re the front brakes overwhelming the rears was based not on them locking up, but just up to a point of threashold. In that the front would dive more than the rear therefore taking weight of the rears and under turn 'lift and separate' so to speak. Sort of like the old 911 syndrome.

Oh, here's a pic of my car. Do you think it looks straight?

 

Patrick,

You have some wrong info on the Racers Edge Camber Plates. I have them and I can get easily 4 degrees plus on the front if I want it. Don't forget that the camber changes with ride height. If you lower the car you get more negative camber for the same plate position. Also you still have camber adjustment on the bottom of the strut to add to the additional camber adjustment on the plate. 2.5 degrees might be the range of adjustment, not the absolute figure. i setup the camber adjustment on the strut so that my camber plates give me 3 degrees inthe middle of the adjustment range. That way I can go either way at least a degree.

Karl knows what he is talking about. He has helped me with my setup all the way through. I have all his stuff on my car. Don't use my example of spring rates though, as they aren't applicable to a track driven street car. Unless you are running very wide true racing slicks on smooth tracks on a race only car you don't want to run as stiff as I do.

"Quite a minimal change" for bump steer means what? Might be ok for a street car but for track I would want 0 toe change over most of the travel range.

What size/type tyres are you running?

 

May not be the total problem, but looking at your initial figures I would say your uneven front caster and lack of rear toe in certainly weren't helping.

 

Ah ok Steve, I see what you're saying re the RE plates. I've sent Karl an email too so I'm sure he'll clear it all up for me. I have a bunch of his stuff on already too. Almost all the rubber bushings have been replaced by metal.

It was all a bit hurried when I collected my car but I believe on the chart 'quite minimal' refers to the Toe curve change listed.

Tyres at the moment are Nitto NT01 275/18 all round on the Enkeis 10" front-rear. Car weighs approx. 2900lbs with no driver and half a tank of fuel.

Springs are 630lb/in front and 710lb/in rear spring/T-bar combo.

 

I think your spring rate relationship front to rear isn't right for a square tire setup. You possibly need to make the front end work harder. I suspect you need less rear roll stiffness or more front. Your car may be just plain tail happy.

Where do you have your Tarret bars set at the moment?

 

This can make a difference in my my experience.

 

Ditto on Karl P. All of my base set up information and all of my suspension parts came from him. My camber plates are set up like Dubai, currently running 3.2 with adjustabliity in both directions. My reason to increase negative camber is to comabat late race push. Karl has great parts and he knows these cars. By the way, I'm running 1000# springs in the rear and 850# in the front. 245/35/18 front, 285/30/18 rear, and very stable under braking with big black brakes/Hawk DTC 60 pads. There should be no difference in stablity with 285/30's in the front.

 

Hi Patrick,
Great thread, lots of good info here. I’m glad your alignment shop fixed the uneven L-R caster settings and added more rear toe.

I agree with what Van stated earlier,

“Patrick, another suggestion for you, to settle the rear end under braking, would be to change the pitch of the car. By raising your front spring perches by a few turns, and lowering your rear spring perches a few turns, you'll "tilt the car back" which will give you less weight transfer away from the rear wheels in braking - thus giving you more rear traction/stability.”

However, since you already adjusted/raised the front of the car, then to adjust the pitch of the car, now all that is needed is to lower the rear of the car.

It may just be the angle in the picture, but to me, the car in your avatar looks too high in the rear. My recommendation would be to make that your next priority and get that checked.

Marlon

 

Thanks guys. Lots of excellent information and feedback. Very much appreciated. We will try a few of the changes and see what happens. More's the pity that you can only really see the nature of these changes while running hard on the circuit. Now where did I park my test track???

 

Dunno how low you are at the front, I lost most of the squirrelly feeling after putting these steering arm joints in (made by shark in germany). They (Shark Motorsport boys) told me the following: " when lowering your car by 40 or more mm the pushrods from your steering to the wheel carrier begin to make an important angle. This angle leads to toe changements when the front wheel is loaded or unloaded (cornering, braking), hens to nervous car response in fast corners or under heavy braking. To avoid this behavior we developped the longer connection ball joints (Spurstangenköpfe) which are decreasing the rods' angle. If you do not feel happy with your car because of above mentioned circumstances you will definitely feel the difference. Imagine, you have the feeling that you can steer your car with one hand under heavy braking....."

So i put them in and that helped a lot. Further I agree with Dubai, think you should stiffen up the rear a bit in relation to your front.

have fun

 

Henk, I'm pretty sure that the Racers Edge A-Arms come with longer and wider pins if this is what you're showing here? Perhaps Steve can confirm? Actually re-reading what you've written I see that these are steering arm pins. I'll have to check into this. Do you have a link to these Henk?

He is also saying to stiffen up the front, not the rear from what i can tell, in the pursuit of a less oversteering setup. I am going to try and get to a track day soon just to see what these latest changes have done. I'm trying to find a 2nd hand set of camber plates otherwise I'll buy some new ones.

Car is looking 'Boss' Henk!

 

i would throw the camber plates you have inside the engine bay on adaptors and turn then 90 degrees and go up to around 5 deg ress of caster .. and +1 to having more rear rate as these cars change to much with rear travel

 

The germans think you shouldn't use the longer pins on the a-arms, he said that the camber changes are minimal due to the angle of the mcpherson and they found the effect of the steering arm joints much bigger. Now, what do I know? I do know they race theirs on the ring and hockenheim a lot. Their spring rate suggestions work very well for me. I'll email you some correspondence for your info.
www.shark-motorsport.de

 

pat the racers edge arms have a longer ball joint pin . not steerring arm pin but that longer pin you have does help make your toe curve change or in other terms changes the bump steer ..the parts pictured above are rack ends ... and to complicate it further its not simply the angle of the steering arms its the angle of the steering arm compared to the angle of the the control arm wich results in toe change (bump steer)

 

I have it on very high German born authority that long control arm pins are a good idea to correct roll center create anti dive control scrub .