reno928s

Sawood 12, I agree with you. I had an 84 928 S Euro and it handled extremely well at high speeds or tight curves. It weighed in at 3600 pounds and it deifinitely felt very well planted sortof like the M3. Even with all that weight it still felt nimble. I was always curious why the 944 never handled the same as the 928.

anders44

yes, adjustable in pretty much every way

333pg333

The planted feeling of the 3600lb 928 was self evident. The 944 would still be more nimble though.

333pg333

This is an excerpt of an email from Karl. It goes on to show the way to calculate the effective rear spring rates at the wheel. It was in reply to some numbers given to me by someone else (Bob) and Karl was correcting them. I wanted to know the conversion of my front springs 110N and my rears 50N + 25.5mm t-bar:

"Patrick,

I have not spoken with Bob, and actually don't know who he is. But believe me, my numbers correct (or close to it - see the following explanation). The info on Paragons site is stuff they got from me a few years ago. In any case, the 47% is a number that I have calculated By taking measurements. I am now pulling out one of Porsche's own Motorsport sheets that shows all the rates of their Turbo and "Cup" cars back when they ran competitively. Porsche lists the 25.5 mm bar as 31 N/mm which is 177 lbs/in. They also then give the variable rate coilover helper spring rates at 34-65 N/mm which is 194 lb/in - 371 lb/in. They then give the total Rate at the wheel(T-bar plus coilover) as 45.4 - 58.5. Back out the rate at the wheel due to torsion bar which they list as 31 and you have 14.4 - 27.5 at the wheel due to the coil over. So take your pick, 14.4 / 34 is approx 42% or 27.5/65 is 42%.

Bob is right about them being inboard but his numbers are off. Actually they are correct I think in that the motion ratio is about 65%. But when calculating wheel rates from spring rates it is the motion ratio squared that is uses. So 0.65 ^2 is , guess what,... 42.25% which is the number that Porsche's own sheet claims as I outlined above. So your torsion bar is 177 at the wheel, and your helper spring rate is a 285 which is 119.7 lb/in at the wheel. So working backwards 177 plus 119.7 is 296.7 pounds per inch at the wheel. Divide this by .42 and that is you equivalent coilover, or 706 lb/in coilover (initially I had 661 lb/in which is attributable to my measurement error - I had 47% and Porsche lists it at 42%).

So it may be a bit stiffer in the rear than I might run but with the ability to tune sway bars etc... you should be Fine. Your setup is actually much stiffer in the front than the Porsche cup setup which ran progressive front springs (200 - 371 lb/in) with the rear setup I described above which is not that far from what you have( yours is 296 at the wheel and theirs was 259 - 334 lbs/in at the wheel).

Hope this make sense, but believe me, what is above is 100% correct. I can fax you the Porsche motorsport sheet if you think it will help.


Karl Poeltl
Racer's Edge

xsboost90

one big thing ive noticed is the difference between tires. My former n/a handled great, but when i swapped wheels to some w/ yoko es100's on them, i felt like my car was real skittish and handled poorly. With the slicks on the car, it was very balanced and tossable. When i sold those wheels and got some Toyo T1-s tires on different rims, suddenly my car was very sticky and i felt much more confident in its capabilities. Now im running a much more solid suspension on my turbo- 400/375 coilovers w/ rear torsions(indexed) and MO30 968 sways, 968 castor blocks and much wider tires. I have no problems keeping up w/ the BMW's and newer porsches on the track- well at least the ones in my DE class.

M758

No conspiracy. The 928 was the top of the line $$$$$$$ car at the time. 924 was the entry level car. They did not want to drive up the price of the 924 using expensive 928 parts. Simple.

Trucho-951

HIGHBOOST, what are you trying to achieve?

The formulas are the easy part (a Rennlist search will reveal many sources, e.g. http://website.lineone.net/~dmsims/9...eparation.htm), the hard part is figuring out what you want the car to do.

I think it is of outmost importance that the driver have a clear idea of how his car behaves at the limit of tire adhesion, a good clear picture of the baseline setting. Before turning a wrench to begin tunning the suspension, it is better to turn a page of a book that explains high performance driving technichques, for example, Skip Barber’s, “Going Faster”, or taking driving classes like those offered by Russell Racing, or Skip Barber. The driver needs to truly understand what tools he already has available as driving techiques to influence weight transfer and thus vehicle dynamics.

Only then, would it be wise to start tunning the car’s suspension. Like they say, “it is easier to tune the suspension than to tune the loose nut behind the wheel”….

One of my favorite readings on chassis dynamics is the book written by Fred Puhn, “How to make your car handle”, it is easy to read and contains just enough physics to illustrate examples of how suspension changes affect vehicle dynamics.

On the subject of vehicle dynamics, here is a short and easy quiz to test your knowledge on vehicle handling and suspension (answer true or false):

1. Reducing the amount of body roll while cornering will improve performance by reducing the lateral weight transfer on the tires.

2. When a car rolls, it compresses the springs on the outside tires, which overloads the tires and reduces their effective traction. A car that rolls less will compress the outside springs less, which will load the tires less, which gives them better traction.

3. If you lower a car, it will roll less.

4. If you drop the front roll center and keep everything else the same, the car will understeer more.

5. Springs and antiroll bars are the primary factors that determine how lateral weight transfer is distributed fore & aft (which, together with camber effects, determines whether the car understeers or oversteers).

For answers and more see here:

http://forums.tdiclub.com/showthread...=133342&page=3

enjoy.

anders44

I just checked my springs, rates are n/mm not n/m like I though

front 80 n/mm
456 lb/inch

rear
50n/mm
285 lb/inch

what you got 333pg333?

after a tip from Mikjel I think they messed up and gave me a setup with torsion bars.

sweanders

I would say that it is possible to make a 951 handle better than most new sports cars. It just takes parts, skill, time and money. It's proven that they can be made to handle very well.

333pg333

Mine are 110N front and 50N rear but that was in conjunction to having the t-bars in at 25.5mm. You had better talk to Michael Grassl.

Tms951

I was at Lime Rock for a track event last weekend for a track event. I run in the top run group with over all is pretty fast. In it with me was a 996 GT3, when I asked him if he had modified the car he said he had replaced all of the suspension components with after maket stuff. My 944 has escort cup suspension with 500lb springs in the front and 600lb in the back, I also have M030 sway bars. My car weighs 2800lbs. and is corner balanced. We were both on Pilot Sport Cup tires, his were a little wider but not much. He was about as fast as me through the turns. I was averaging about 1.05.xx minute lap times. It was only my second time at the track in this car, and I only have about 5000miles behind the wheel of a 944 all together. My fastest lap time was 59.082 seconds, this is very good for limerock and I would assume faster than any of the GT3s laps, I think he was doing fairly consistent 1.04.xx laps.

TurboTommy

Trucho-951;

I have also read Fred Puhn's book, and it's very informative; and that being said, #3 question in that quiz doesn't seem right; the answer should be "true". I went to the link and read that info and I think the author is got something screwed up.
It's the height of the Cg in relation to the point of contact between the road and the tires (not the axel height) that matters. The CG is always higher and therefore there is always weight transfer and it will cause the body to roll about its roll axis.
Watch F1 cars go around a corner. Also, the reason they have negative camber is to counter-act the body roll.
So, yes, if you lower a car it will roll less, all else being equal (lower CG, therefore less weight transfer).

reno808

NICE DRIVINGGGGGGGGGGGGGGGGGGGGG. I knew it can be done..

Trucho-951

The author of the quiz is making the point that it is the height of the Cg in relation to the "roll axis" (or roll centers) that is important. In his simplistic example, the roll center lies exactly midpoint of the solid axle. He is using a solid axle suspension because it is the easiest way to help someone visualize a roll axis, which as you probably already know, for other suspensions is an imaginary point in space.

Page 35 of Fred Puhn's book defines roll centers this way: "To find the roll center for this suspension, draw lines between the center of the tire contact patch on the ground and the instantaneous center for that wheel. Do it on both sides of the car and extend the two lines until they cross each other. The roll center is the point where the two lines intersect." See Figure 8A.

Tommy, I'm glad you found Fred Puhn's book informative, I keep going back to it, because even though it is very simplistic, it covers so much and most of it can be put to practice quickly.

MM951

Are you in the pca or scca?