ptuomov

No, thanks BC. I definitely don't want to move along without understanding at least a bit about this. I think this will get me on the right track, had not considered the difference between spring rates at the spring and at the wheel, which with hindsight is such an obvious thing.

dr bob

Tuomo-

The lever arms end at the bushings inner, and bushings outer rear, lower balljoints outer front. This is tape-measure math and a little trig for the shock angles. Rear is more fun with the multiple pivot points. Unless you are modeling all the travel, this stuff will be not so valuable. No matter what, a 300lb/in spring --at normal position-- will be half as stiff as a 600lb/in spring at the same position.

ptuomov

But how should I compare front vs. rear? I think I need to know those. If the leverage ratios are different in front and rear, me just blindly copying the relative spring rates from some seemingly similar sports car is going to be a complete crap shoot.

I'll definitely have to think about this much more before committing any cash.

fraggle

My advice: if you drove one you liked, copy it. If you want a development project, read all the other advice here and bet your $$$.

I like my ext adjustable koni's with the 600/400 setup and adjustable perches.

hacker-pschorr

+1
Not to mention suspension and chassis setup is one of those black arts. Just because it "feels" faster, are you sure it's actually going around corners any better?
IMO the "butt dyno" is far more misleading when it comes to handling than HP mods.
This is a subject where someone like Mr.Simard is such a valuable asset, he "gets it" in a way I will never fully understand.

I'm going to stick with my stock sport shocks and upgrade the springs thanks to Mark A - then go with the 928 Specialists Sway Bar.

After that I'm not really sure. Maybe bug Mike Simard some more about copying his control arm bushings

I think you are on the right track, problem is you just might have to bite the bullit and do some trial and error.

Hilton

Interesting comments Mike, and supports some of the info on our local mailing list.

One of the aussie 928 owners has a GT with a custom setup of 1200lb front, 600lb rear hot-forged springs on it, and externally adjustable Koni's (can't remember if they're custom valved). He bought the car from an owner who had the setup worked out by a race shop for street/track use.

A bunch of the other 928 owners have driven it and all lust after his ride quality - firm, but not rough and doesn't jolt or rattle teeth even on our crap roads.

Some discussion on our local 928 mailling list about the wheel rate ratio (0.83^2 I think for the front?) and effective spring rates puts 1200lbs at around 830 effective.

That coupled with the fact that being hot-forged makes a difference too apparently?

abrexrode

Hot forging changes the molecular structure of the metal (Makes it stronger).

dr bob

We've kind of ignored the effects of anti-roll bars on net spring rate when cornering. If you do enough reinforcement to the frame brackets, a beefer (read: MUCH beefier) anti-roll bar will do a lot for apparent handling without doing so much to your fillings. Just do both ends of the car together so you don't end up in a wall one-end-first someplace. Carl's splined front torsion bar with the hard levers is a nice piece with a good bit of tunability. Anybody using that on a street car?

Vilhuer

Based on one example I wouldn't go higher than 500 350 on street car. 600 400 with Leda shocks on SC'd S4 is too hard for local rods. It will come out and Bilstein/Eibach will go in later this year. Leda's will go to racecar build which will be road legal.

blown 87

With the exception of very few here i am willing to bet that goes for most of us here.
i know very little about this stuff, so this thread is a great thing for me.

stuartph

I have leda's 800 front and 525 rear plus carls front anti roll bar and brackets on the rear, for me the car is perfect and not to stiff for our rubbish UK roads.

This set up has totaly transformed my car for me its not far off a large go kart

slate blue

I find my 600/400 with adjustable Ledas quite stiff in a slightly lighter S body. Even turned right down with very little damping they are still stiff and you will crash into bumps. I agree with Errka and another aussie rennlister has that setup (500/350) with a GTS and says it is great. Earlier cars I would go with 400/250.

Greg

ptuomov

In terms of noise, vibration, and harshness, is there any real impact from going from the rubber shock/spring mount to a solid, ball jointed mount? The reason why I am asking is that the joint is isolated from the wheel by a spring and a shock. I am naively thinking that the racersedge mount you linked to is not going to have much adverse impact on NVH while allowing the spring to control the total spring rate and the shock control the dampening, instead of the mount doing some springing and dampening as well.

I've been baffled by my own ignorance on this topic, so I order a couple of entry level books from amazon.com. Let's see if I can make any sense of this suspension stuff.

hacker-pschorr

AFAIK all of the 944 camber plates use a spherical bushing, running those on the street is a very popular option.

There are a few threads discussing this in the 944 and 951 forums, here is a recent one:
https://rennlist.com/forums/944-turb...er-plates.html

One possible downside is lubrication, need to make sure that joint doesn't go dry. I doubt that is a PTFE lined bearing like Mike Simard uses with his bushings. If it were, kinda odd they don't mention it.

Cheburator

I have used the solid front bushings from 928Motorsports for about 5000 miles on the street and track and there has been no problems. The Leda shocks are rose-jointed at the bottom too...