Porsche 917/10 & Performance Trends Suspension analyzer

[SSLance]

Ron Sutton posted shots like this from Performance Trends in my build thread.

He may be able to explain how it was done.

[csdilligaf]

Well I have been playing with the Suspension analyzer and think I can attach the file. If you have Suspension analyzer please try to open it. I was able to click "File" "Save as" "Advanced" and pick a location outside of Suspension Analyzer and save it. Then I was able to open Suspension Analyzer click "File" "Open from floppy drive" and locate the file and open it again. I guess they just never bothered to change the language. I have not had a floppy drive for 20 years. Also I have no idea of the exported file's type but was able to put it in a zip folder to post it here.
So, please if you can open this do so and see if it works. Keep in mind that I am new to the program and this is just a rough start. There are lots of info to be corrected still but I am trying to nail down the basics of the front suspension.
I have read that for a car like this I may want to account for 1" lift and dive and 2 degrees roll for the calculations. Does this sound about right?

[csdilligaf]

I've been working on the suspension in CAD and had to make changes so the upper arm does not come in contact with the wheel at full lock doing an 18 ft radius turn. I am thinking about no anti dive or squat. I figured out how to print screen into paint and post it. Still lots of spring rate, roll bar and other things to be worked on obviously but what do you think of these numbers with 1/2" dive, 2 degree roll and a tight turn? Am I getting closer?

[David Pozzi]

I haven't looked at the file but none to a little anti dive in front will work. A low CG car like that with high rear weight won't have a lot of dive transfer anyway. The rear needs anti-dive anti-squat. With IRS you won't have much anti squat effect due to drive train housing torque like a stick axle car, but it needs as much anti-squat as you can get. I expected to see 60% rear weight, would like to hear your comments on what you think a good rear weight percentage is.

On your front lower A arm, I would not use rod ends on the inboard ends. I'd make them spherical bearings in a housing welded to the arm ends and jig weld them so they are identical. There is going to be a lot of front to rear loading on them from braking and side loads on rod ends will wear them out or break them in time. Do all your adjusting on the upper A arm.

To get at your suspension files, open your Perf Trends folder, look for 3D data. It should be in there. Something like C:program Files/Performance Trends/Suspension Analyzer/3-Data/ then pick Examples, or My-Tests, or make a new folder. It's not good to store files elsewhere, the program can lose track of them according to a warning they included in earlier versions I've had. You can make a new folder for your personal projects, but keep it inside the 3D-Data folder.

I just got the Brian Redman book and he stated the 917 Prototype was aerodynamically unstable. The fix was to raise the tail to increase rear downforce. Perhaps the wing used in the photo and the small lip spoiler helped enough on the car in the photo but be aware of the issue.

[csdilligaf]

Thanks for the input. I am still getting used to Suspension Analyzer and getting better at it. I have been working on a new KPI/Castor combo with a 5 degree kingpin and 7 degree castor. That's the great thing about using software is I don't have to make each change and try it out. I am trying to get my castor gains correct for each front tire and think I am still a little off. With 1" dive, 1 degree roll wheels at a 15 degree turn I have -1.93 degree on the outside tire and .94 degree on the inside tire. Where do you think I should be?
As for the Aero issue, yes the 917 Lemans cars in 1969 had a little wobble at 240mph on the Mulsanne straight. They changed the tail shape in 1970. The Can-am cars never got to that speed and were shaped like the first picture of a 917/10. As for the weight balance it helps to have me(200lbs) so far forward, the pedals are actually on the center line of the front wheels along with the battery, radiator and two sidepod fuel cells in the front half of the chassis.
Here is the latest changes.

[David Pozzi]

I’ll take a look at your file when I get time. I recommend consulting with Ron Sutton to get some help. I did see on the previous file, the roll center moves outboard with 2” dive & 2 degrees roll. It would be better to have ithe RC stay closer to chassis centerline or move towards the inboard tire. I don’t know how to accomplish it though. Your dynamic camber looks very good. I’d read Ron Sutton’s sticky thread in this forum for what he likes.

[csdilligaf]

Yes, I have been reading Ron's thread on front suspension, about 1/4 way into it so far, I want to really soak it in so have been re-reading over and over. I have a post in it on the last page and Ron has gave me a little input so I am working on making changes but struggling a little with it. I would have thought 2" of dive and roll would be more than I would get from a purpose built track car that is mid engine and with a flat 6 the center of gravity will very low. Other than fiberglass there is nothing above the top of the rear tire other than the roll bar and my helmet. I am going to try to calc the CG but have not figured that out yet. I assume Performance trends can assist with that? What do you think I should account for with dive and roll? I would be happy to end up anywhere near the 917/10 or 908's handling ability. I don't even know if there is much now days that can keep up with a 350 hp 908 on most tracks. But I am having fun with diving this far in trying to get the best handling I can.