First, I must say the 928 is a well setup car in stock form. It was designed to comfortably cruise at triple digit speeds with safety in mind.

Second, I do not consider myself a suspension or driving guru. So what am I? I'm a Porsche enthusiast that likes to drive my Porsche around town, on highway trips, participate in club tours, autocross regularly, and do the occasional track DE. I've owned a 914, 944 TurboS, 928 GT, BoxsterS, 944 Turbo, and 928 GTS in that order. I enjoy having very nice and comfy daily driver that presents well at car shows, can keep up on high speed tours and DEs, and be competitive for FTD at an autocross. I've done that in all of the cars above with the exception of the 914, I hadn't yet discovered the adrenaline rush of autocross when I owned the 914.

What I've learned I learned taking the 944 Turbo S from being the slowest car at my first autocross to being the one to beat. Part of it was learning to drive fast, but there was a point where suspension upgrades took me from competitive to being fastest. When I upgraded the 944 suspension I was not looking for a dedicated track suspension, but an all round street/occasion track setup that was better than the stock setup. What I ended up with was a comfortable street car that was as fast or faster than anything at the track.

Street/Track Setup Thoughts

Alignment
Start here. Before doing any upgrades to your suspension make sure you have a good alignment and proper ride heights. Negative 1.5 front camber and negative 1 rear is a good aggressive setting that will increase cornering grip and remove some of the understeer without effecting tire wear too much. Stock caster and toe are good, with maybe the toe as close to zero as possible if you don't mind a little trammeling on the street.

Springs
Springs are for compression. As long as they do not bottom out against the stops they are stiff enough. Usually one step up from stock will keep the car from bottoming out because of the higher loading driving faster around corners at the track, but not so stiff as to make the street ride too harsh. Many make the mistake of putting stiffer shocks on instead of stiffer springs making the shocks do the job of the springs. This will result in a better handling feel on smooth surfaces like a track, but will make the street ride much harsher than doing the job with springs.

Sway Bars
Sway Bars control the roll of the car in corners, but they also control the front to rear balance of the car in the corners. With stiffer springs you will need stiffer sway bars to have as much effect on the roll of the car. It is important to have adjustable sway bars so you can tune the balance to be neutral in the apex. I like to drive a circle slowly increasing speed until the car breaks loose. Whichever end breaks loose first, the sway bar on the opposite end needs to be stiffer. The front and rear should break loose at the same time making the car slide out to a larger radius turn. Lifting the throttle when it breaks loose should let the front grab a little better and the rear rotate, but not too much. Any time you change wheels or tires or the tire width stagger you should recheck and adjust this balance. This is what makes the car agile and lets you throttle steer through the apex of the corner.

Shocks or Dampers
Again, if you upgraded your springs, you are going to have to upgrade your shocks to be able to control the bounce of the stiffer springs. I like shocks with adjustable rebound. The rebound helps adjust the balance on corner entry and corner exit. Rear rebound adjusts rear grip on corner entry and front rebound on front grip on exit. If front rebound is too soft the car pushes when you get on the gas to exit the corner. If the front rebound is too firm the rear tires spin as you get on the gas. If the rear rebound is too soft the rear gets too light and the car tries to swap ends as you brake into the corner. If the rear is too firm the front brakes break loose to easily and the rear won't rotate at all to point the car at the apex as you turn in for the corner.


My car is a 94 GTS. It has the following:
Hypercoil springs 600/400
Devek adjustable front sway bar
Louie Ott rear drop links set for full stiff on stock rear sway bar
Koni Red externally adjustable front and rear shocks.
235/40/18 front and 275/35/18 rear Dunlop Direnza Star Spec Tires


My driving style is what I have found to be the fastest for a 50/50 car. I brake into a corner slowly lifting off the brakes on turn-in. Letting the rear rotate and getting on throttle just enough to check the rear rotation, but not enough to set the rear tires spinning, and put the car into a 4 wheel drift. Throttle steer the slight 4 wheel drift through the apex. Add power as I exit slowly unwinding the steering but still letting the car drift to the outside of the corner until once again going full throttle down the straight. It takes a lot of practice to get the braking zone right so the car is still front biased for the rear to start to rotate and still be going fast enough to setup the 4 wheel drift as I turn in.

 

Good thoughts Richard!
Are the externally adjustable Konis valved different than the internally adjustable Konis? I really like the internally adjustable ones on the Stepson, the '89, and on the front of the Jalapeno. My plan is to put the same on the GTS. Just wonder if they handle differently.

 

The externally rebound adjustable Koni Reds are the same as the internally adjustable Koni Reds. They were converted by Koni from internal to external adjustable. Some sort of special deal done by Devek back when they did the suspension on the car. All I added was the Ott drop links. Not sure why the rear sway bar was still stock. I am super happy with the externally adjustability lets me tweak the car for the course. Tighter corners need a little more front rebound firmness to keep the understeer away on acceleration. Bigger corners need a little softer front rebound to keep the power oversteer at bay. The adjustability lets me tune the car for the average of the turns in the course.

 

I guess I could do the same with mine, then, just not as conveniently.

 

thanks for the write up ...many things with suspension set up seems greek but your write up really helps.

and explains why with stock springs on my gts and changing to bilstiens for shocks harshened up the ride.
Question---If I put 600\400 springs on would the ride stay the same around town but feel more controlled at high speed. or just no diff around town
andy

 

Since you already have the Bilstiens I feel the ride around town would be about the same as it is now. A little firmer but not enough to be called harsher. The shocks try to stop abrupt suspension movements and that is where most of the harshness comes from. The stiffer springs just don't move as much. You will notice the stiffer springs at higher speeds, especially in turns or changes in elevation that load and unload the suspension.

Devek recommends non-progressive springs on the front for high speed driving, Eibach says progressive rear springs help keep the rear tires from spinning when you get on the throttle. I don't think the Hypercoils I have from Devek are progressive, at least they don't look it.

 

Great write up Richard! I will also admit that you have the best looking GTS I have ever seen. Probably the exact way I would set up one if I had the $$$$$$. Joe

 

Thanks Joe. Honestly I bought the car with everything except the x-pipe, RMB, and Ott rear drop links. I only added the rear drop links because the car was understeering like crazy mid-turn. I even went to 235 front instead of 225 to try to tame the understeer and it got worse?. Ended up replacing the rear passenger side control arm to get a good alignment. Weird, the new arm moved the rear wheel/tire out about 3/8 of an inch.

 

Ah ...."Weird, the new arm moved the rear wheel/tire out about 3/8 of an inch. " if the rear arm were bent so that it would not align to spec not too weird that after the arm change the tire location changed. Stiffer springs are ALWAYS stiffer they support the car the shocks primarily keep the springs from continuing to bounce so stiffer springs need stiffer shocks. "Sway bars" try to borrow spring weight from the inside wheel to stiffen the outside wheel but that act unloads the inside tire potentially reducing traction.

 

Yes Mr. Bailey, it is possible to have too much sway bar. I was going to mention that. When I adjust my sway bars...once I get the car balanced going around in a circle slowly accelerating until both ends loose traction at the same time and lifting the throttle will let the front turn in a little more but not too much. Then I increase both the front and rear sway bar stiffness if possible until the speed that the car breaks loose starts decreasing. Then I back them both off just a little and make sure the front and rear still break loose at the same time slow accelerating around the circle.

On my 928 the rear drop links only have two holes stiffer than stock. I put it on the stiffest and balanced using the sliding front Devek bar. I may need to try backing the ott steroid off a hole, rebalance and check my skid pad circle break loose speed. I might gain a couple mph corner speed.

This took much more time with the Weltmiester sway bars on the 944 Turbo as the adjustment was a collar that slid on a shaft where the drop link attached to the bar. Once I got it balanced, I just kept sliding the collars stiffer until the break loose speed started dropping then backed it off. Having the sliding collars both front and rear let me tune the corner speed just a bit higher than only holes.

 

great thread......I'm still learning suspension tuning, but here is my impressions tuning the widow, lemons racer and comparing to stock 928's and different suspension setups.

The lemons has the "sport" shocks which are bilsteins with cut springs....so it is very stiff spring rate, but I don't know exactly how stiff...it runs on stock 16x7x65mm rims with 225/50-16 Dunlop Direzzas like RKD uses...stock sway bars and alignment set to 2.5' camber all around with max caster up front and just a slight toe in at rear (1/8th inch) it is around 2750lbs, so its fairly light compared to a full weight 928....I'm also happy with the rebound damping of the bilsteins, its better than the konis in the widow

I was pleasantly surprised at how well the lemons racer handles..yes its under tired...but turns pretty well considering such small street tires....it turns in far quicker than any full weight street 928 I've driven and seems to have at least as much peak grip if not more....it also is fairly neutral...only a slight push

Sharky ran the same wheels as RKD (CIII's) with stock Conti sport contact II's in 235/40 front and 265/40 rear....not the best tire, but not bad.... 100% stock non sport suspension with stock alignment...it ran well on track, but would understeer pretty heavy when pushed hard....

The widow is my best handling 928 by far (when it runs)....internally adjustable koni reds, with 800F springs and 300R, stock sway bars, but Carls adjustable drop link-tow hook set 1 under full stiff....front tires are 295/30-18 Toyo R888's and 335/30-18 rear....it does understeer at slow speeds, but not that bad considering the tire size differential and spring rate differences...I do need to increase the rebound damping quite a bit...since it rebounds a bit too much for my taste... front camber is about 2.1' with max caster, rear is about 1.8'....after 29 heat cycles on the R888's tire wear is excellent....I'd say at least 50% remaining.....

I also got to drive Seans 87 5 speed with bilsteins with 600F 400R springs (like RKD) with Carls race front sway bar and drop links rear set full stiff...running toyo R888's 265 front and 295 rear...front caster is maxed and camber is about 1.4' front (which is max)...not sure on the rear....it does handle quite well.....its a full weight street car, so it doesn't turn in as quick as the lighter 928s...but does generate good G forces with nice solid feel I expect than from a 928.....it also rides quite nice on th street...as I also got to drive it on the street too......I would say thats about the ideal street+trackday toy suspension setup for a 928....

 

Understeer/Oversteer is difficult to manage. Any setup is going to have a corner speed range or sweet spot that it is neutral. The tendency is to understeer on slower tighter corners and oversteer on larger faster corners. That's why when I do the circle thing to balance the sway bars I try to use a circle radius equal to an average turn I will be negotiating when driving at the limit. Then at each event I can fine tune the neutral handling sweet spot by adjusting the front rebound to control throttle on understeer and rear rebound for braking oversteer.

To rid the lemons car of the slight push you might try setting your rear toe a bit closer to zero, I found those Dunlop Star Specs really sensitive to alignment. I have both front and rear toe set as close to zero as possible without being positive. And I thank Mark Kilbort for the tip on tweaking the rear toe it helped me tune out the understeer I was fighting after going to the Dunlop Star Specs even though I had reduced the front to rear tire width stagger.

 

What is a good starting point for the Koni's? I do not have them in the car right now, but will put them in come springtime. Do you just turn the adjuster clockwise until it stops and then turn them counterclockwise a specific number of turns? Joe

 

That's the way Koni recommends adjusting them so you are sure both are the same on each end. Since the adjustability was initially designed so you could firm up the shocks as they got softer with age instead of actually tuning the ride, I would start at about 1/4 of the adjustment and see how the car accelerates in a corner for the fronts, and brakes into a corner for the rears.