A major improvement would be to change to double-wishbone suspension. Those can be customized so the camber-change curve keeps the outside-tyre vertical as the suspension compresses and the car leans. In which case, minimal negative-camber is needed initially because the tyre stays vertical and flat regardless of lean-angle. I'm looking at the 928's front suspension, would be interesting to transfer that over to a 944.

I appreciate the comments. I also understand that there are a lot of variables. Therefore I was just asking for approximate numbers compared to the stock. Now I have some direction. I will use Danno's numbers, also consider your comment about the rear toe and will see how the car handles and how the tires wear on the track. Could this also might provide some useful information? I have very little experience in this field. E.g. with fully stock suspension and stock alignment I noticed that after some 40 miles on the track the outside (the edge) of the tires was quite worn.

As I participate in the youngtimer events, one of the things to consider is that I should not make significant changes to the car (such as coil overs etc.), thus I will try to get the best results from close to stock suspension.

Yes, that's from the positive-camber under full-lean & suspension-compression in the corners. This is what the initial negative camber counteracts. Pyrometers are cheap nowadays, very valuable tool. Measure outside, middle and inside of each tyre's tread immediately after getting off the track (12-readings total).

I'm building a setup with 12 IR-sensors to datalog tyre-temps in real-time. There's not even an optimum setting for each track as each corner has a different "fastest" setting. It comes down to how much time is spent in each corner and down the next straight. We'll want to maximize suspension-settings to get in & out fastest in the corners that takes the most time and also the ones with the longest straights.

At some point with real race-ready wheels of +10" width and racing-slicks, the cornering-G can get high enough that the weight-transfer under cornering is 100% to the outside wheels.

http://i42.photobucket.com/albums/e3...1-WheelsUp.jpg

In which case, you not only have to adjust camber for the lean-angle, but also for the lift-angle! ;)

Also flash968 is right on. Corner-balancing makes a difference, especially if you notice the car understeering on left-turns and oversteering on right-turns (or vice-versa). Many alignement shops don't understand corner-balancing and try to get even left-right or front-rear weighting (which is impossible anyway). You want cross-corner balance where LeftFront+RightRear total weights equals RightFront+LeftRear with the weight of driver in the seat and 1/2 tank of gas.

yeah - the gadgets we used actually measure the suspension travel and geometrical changes. that gave us a baseline to start working with. then it was a process of shock and tire adjustments, but the suspension geometry and setting was essentially was done. like i said, pricey and time consuming, but it worked very well, and eliminated a lot of the guesswork and fiddling and replaced it with math.

on these cars, bracing the lower mounting points eliminates the chassis compression and allows the use of a lot less negative camber, as you no longer need to correct for that. it has been truly amazing at the difference. it has also resulted in much tighter turn in and more responsive steering, as there is no more flex there. slalom speeds went up significantly.

Got it, same page now.

lol - it would have been a lot easier with my easel and white board and pop ups

As sI said, I have no experience with alignment setting numbers. I read the theory on Wikipedia and some other sources to understand the basics. I looked at the owners manual to understand how big difference is between stock alignment and one that works on a track. According to it:

front chamber should be -20' +/- 15'
rear chamber -1º +/- 5'
Toe in front +10' +/-5'

Could you someone help to understand how to convert -20' to degrees? Is it 20/360 i.e. 1/16º?

360' = 1º ?

In other words - does 1/16'' toe in as mentioned by Danno above correspond to 20' according to way how the numbers are showed in the 944 owner's manual?

Thanks.

it's already in degrees. -20' is "minus 20 minutes", or 1/3 of a degree negative

for what it's worth, here's what we do for an improved street setup:

first - get your ride height even at all four corners and then corner balance the car

then - on the front:
1 degree negative camber
castor maxxed (also usually .4 degrees less on the uphill side of a crowned road if you have those where you are)
1/16" - 1/8" toe in

on the rear:
about 1.25 to 1.5 degrees negative camber
about 3/16" toe in

Converting between radial and linear measurements isn't a constant ratio. For small changes, you can use 60'=1º. So -20' = -20' (1º/60') = -0.33º. However, as the angle changes more and more, the toe changes less and less. Also the ratio changes depending upon tyre-diameter. So best to stick with inches of toe since that's easiest to measure.

Remember that everyone's car is different. You don't have a really stiff-springs or tremendously lowered, lightened car with braced frame and chassis. You'll want to start with settings on a car that's as similar to yours as possible. Then gather data from actual in-the-field usage such as tyre-pressure, tread-temps, wear-patterns and lap-times. So start with:

1. your existing settings - pressure, alignment, etc. Write this down in a log with dates so you can correlate it with other data

2. usage-data and wear-patterns - you already have concrete info as worn outer-edges. Write down any other pertinent data.

You can't arm-chair race and get to "perfect". It's a fine-tuning feedback cycle of monitoring actual performance and making adjustments to see what effect it has. At this point, you have more than enough info. Do not try to change anything other than going from your existing specs. So... go back to step#1, look at what your alignment specs are, and add negative camber until you have even temps on the outside and inside tread of the outer tyre. Adjust tyre-pressure so that the middle of the tread is the average of outside & inside temps. Write down your new settings and gather more usage-data.

And example of what not to do is not going from your existing specs and data. Let's say your existing front-camber is -0.75º and you read on WikiPedia that a "good" setting is -0.33º. So you change your front-camber from -0.75º to -0.33º. What will happen? Since you already have excessive outer-edge wear from not enough negative-camber, reducing that amount will make your outer-edge wear even worse.

This is where gathering in-the-field data will make much more sense than trying to figure it out in your head. Measure the outside-middle-inside tyre tread-temps at -0.75º or whatever your existing setting is. Then change it to -0.33º and re-measure the temps again and see the change in temps.

Thanks for the advise. As I will have to change the springs and bushings, re index the TBs, even out the new ride height (corner balance, if I will find a shop), new tires also. Thus, the current alignment (should be now within standard specs) will be messed up and I will have to redo it anyway. I will use your guidance for a new starting point and go from there.

I think this thread will be very informative also for others with similar questions.