[Torbjorn968]

I have in some posts voiced arguments for running equal dimensions all around. After corner weight/alignment session of the car it is clear that I have stated the wrong angles used with this setup. It is also clear that my car now with this wheel combo oversteers too much.



Starting of with the belief that I had 3 degrees of camber all around (info from previous owner) and the feeling that a bit less understeer was needed the car was setup with 3,5 degrees forward and 3 degrees at the rear. But looking at the numbers of the meassurements of the angles before the new alignment I had been running 2 degrees forward and 2,5 at the rear and fighting this by setting the rear arb (MO30) at the hardest setting.



With the new settings the car turned too tailhappy with some interresting spins both with me and a team member in my endurance team behind the wheel. This weekend I was running 205s forward since I shared the car with a friend who's never been on the track and the car was fine again.



For anyone interrested in trying the 255s all around it is good to know that my car is setup with 800 lb springs forward and 1000 lb at the rear which should be more oversteery than a typical MO 30 setup if I have understood things correctly. I will now wear out the 205s (difficult to sell) then try the car with 3 degrees all around and the rear arb at the loosest setting when I move back to equall dimensions around the car.

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[flash]

i see this all the time - people throw in a ot of negative camber, becuase they think it flattens out the tires and gives better contact



while this may be true with a stock car, once you start putting in stiff springs and such, the car rolls less, and hence you spend more time on the edges



the key is to determine the highest net contact patch area



i think you may be going in the wrong direction - with that much spring, i would flatten the tires out - the car is probably not rolling much, and hence the need for negative camber is lessened - you are probably actually getting less tire on the ground



i'd try setting the front to 2 degrees and the rear to 1.5



of course the shock and strut settings could easily be doing this too - what are you running that can handle those springs?

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[Torbjorn968]

The shocks are custom LEDAS tuned to the springrates so these match. Soften the shocks too much and the car behaves like "Tigger" (the Winney the Puh tiger) but with the damping set to full the car is extreemly stiff. On track I run the settings 8 clicks from the stiffest with 24 incremental steps to the softest setting. Even with this stiff springs there are some roll, especially whenit gets warm and the tires sticker. I have 1.35 G meassured in normal curves and on the picture attached below with a bit of angle of the surface (what do you call this, English failing me) I have 1.45 G meassured by the driftbox.



With 2 degrees of camber I had significant wear on the outsides of the fronts. Given that the car is also driven on the road and still the tyres wear out on the outsides this should indicate a larger optimal camber for track use.



Just to make sure of my reasoning I importad the pic into a simple CAD programme. The roll appears to be about 2.6 degrees. Which means that I am not so sure.... I also understand that camber increases with body roll. Is there a theoretical reason to have more camber than body roll?



//TL

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[flash]

that shot does indeed show a lot of roll - perhaps it's time for bigger sway bars

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[Torbjorn968]

Bigger swaybars in the pipeline, especially forward. Next season.



T

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[flash]

yeah - i am really liking mine - i have now a 31.75mm up front and a 22.25mm rear - MUCH less leaning and rolling, and am able to reduce negative camber

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[Torbjorn968]

I just got some numbers from Swedish Touring car racing: - 5,5 degrees forward and - 4,5 degrees at the rear. Not exactly soft cars. So there must be a tyre deformation factor here. They run slicks which I think are diagonal tyres and perhaps they deform differently?

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[Eric_K]

Ideally, you should use a tire pyrometer to help tune the camber settings. It will show you the hottest part of the tire (where the most work is being done). You can use alignment settings or tire pressure to even it out. Barring a pyrometer, you can try to read the tread wear. It can take a lot of laps before you can see what is happening. I wouldn't try to tune the balance of the car with camber settings. Use springs/sway bars/tire pressure for that. The ideal camber settings will be different between types/sizes of tires, the track being run and other mods to the car. The settings can even be different from side to side of the car. For example at Portland, which is predominately right hand turns, the left side tires like a degree more negative camber than the right. There is no substitute for testing different setups to see what works best for you. There are usually many different combinations that will result in a good setup. It is also highly personal, what one person likes is not always what another driver likes.

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[Torbjorn968]

[quote name='Eric_K' post='51337' date='Apr 23 2008, 05:21 AM']Ideally, you should use a tire pyrometer to help tune the camber settings..... There is no substitute for testing different setups to see what works best for you. There are usually many different combinations that will result in a good setup. It is also highly personal, what one person likes is not always what another driver likes.[/quote]



Good answear. Will meassure temp.



I think a problem as a beginner is that you may be tempted to start to fiddle around with settings when it is something wrong with your driving style. Therefore I think it is important to find one base setting and then adapt to that. Once establishing a consistent drivingstyle then tuning the car would be productive again.



So no over to the potetially fiddling around too much department:



Tyre wear at the rear is substantial at the inside of the wheel with the big cambers I have run aft. But according to the previous owner that is not a pure camber issue but camber combined with toe. According to him rear camber was chosen to maximize grip cornering, the wear on the insides occuring on the straight, in breaking, accelleration and perhaps on the inside wheel.



I have some adjustment range at the rear swaybar and I understand that with the rather stiff setup my car has especially the forward swaybar might be under consideration for changing for more range.



I also looked up tire preassure in an adjusmtent table on a Swedish forum. It stated that more preassure at the rear would lead to less oversteer. I would think the contrary: more preassure = less contact area.



/TL

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[mikew968]

I am running around -3.4 front and -2.4 rear. I have gotten to that point thru evaluating tire wear. I still have some understeer with similar spring rates. I am wondering if 255 or 265 front tires would help or even fit.



Mike

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[Torbjorn968]

255s work no problem, see pic of my car cornering couple of posts up. You run 225s forward and 255s rear?

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[Eric_K]

T - I think you have too much rear camber. On the track you should have pretty even wear across the tire. Using track camber on the street will result in inside tire wear since there is not a lot of cornering involved. Mike's camber numbers look more in line with what I typically use. I run 255 Toyos or 245 Hoosiers on the front. It depends on the tire. The 245 Hoosier is wider than the 255 Toyo. 275s would fit - with the right setup.

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[mikew968]

I talked with a highly modded 944 owner who on a lark put 315's in the front. (315's on rear as well). He said the car turned in very well and much of the understeer was gone. That got me thinking about 265's if they would fit on the front.

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[Torbjorn968]

[quote name='Eric_K' post='51456' date='Apr 25 2008, 06:35 PM']T - I think you have too much rear camber. On the track you should have pretty even wear across the tire. Using track camber on the street will result in inside tire wear since there is not a lot of cornering involved. Mike's camber numbers look more in line with what I typically use. I run 255 Toyos or 245 Hoosiers on the front. It depends on the tire. The 245 Hoosier is wider than the 255 Toyo. 275s would fit - with the right setup.[/quote]



What angles do you run and what do you run at the rear? Looking for a pure track setup. Will soon get an extra car for street use. If we for a moment ignore balance and consider only grip cornering would it not be logical to have more or less equal angles around the car, maybee a bit more forward for the extra "lean over" during turn in.



Given the ambition to run equall sizes around the car (which ofcourse could be questioned) extra rear grip cornernering will be needed and roll should after turn in be equall around the car. Extra wear on the insides of the rear on the straights is not a major problem since the tyres can be rotated and even at 3.5 degrees forward the fronts will mainly wear on the outsides according to members of the Swedish 944 site (at 3 degrees it certainly did on my car last year, to little time with 3,5 to deduct this from my own car).



best



TL

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[Eric_K]

I currently run 3.1 front, 2.6 rear. I don't think having a ton of rear camber gains anything.

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[Torbjorn968]

Given same body roll forward and aft should not angles for max grip (neglegting balance for the sake of argument) be the same all around?



If we then add ballance into the equation we have, as Erik has pointed out, the arbs and spring rates as a first adjustmentsince the tire should be at the optimal angle against the tarmac for both grip and wear purpulses.



With a 50/50 weight distribution there should be an argument for equal angles with equal tire sizes? Given limited power of our car a lot of the accelleration will be on exiting the corner with high side Gs which means that camber aft should be a good thing for traction in this respect.



T

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[Eric_K]

I think your point would be more valid on a car that had the same type of suspension on both ends. The semi-trailing arm in rear vs. MacPherson strut in the front, have different needs.

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[Torbjorn968]

Different change of geometries under roll?



//TL

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[flash]

yes - the suspension geometry changes as it goes through roll - how much varies depending on the suspension design, as well as components like bushings - the camber angles can change 10 degrees on some suspensions - that is why bracing is so important - limiting camber change is the key to fast corners

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[Torbjorn968]

Attended a Touring car race today and they do indeed use absurd angles (as stated in one of my posts above). Think I mentioned about 5 degrees and that is what it múst be visually being much more radical than the 3 degree + I use. Perhaps slicks is the reason with better grip? But in this race it was cold (9C + which should be low 40s.) and with some rain. But still with the same extreeme angles.



Getting back on track tomorrow evening (oil hose close to the cooler "exploaded" last time).



Erik: same dimensions all around?



//TL

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