A Suspension conversation...
 

I have been driving Leeroy alot. He is my... 7th 928. I love them. One issue I will be concerned over getting right on the 78 project is the ride and handling balance.

The 928 seems to have ALOT of impact harshness. When you increase the sway bar stiffness, and increase the spring rates, and tighten up the shocks, the relatively short wheel base, combined with more rate at each corner seems to combine negatively and create a "bouncing" sensation, but also alot of entire-car-moving impact harshness over expansion joints and road cracks.

I think of all the stuff on cars I don't know about, I know the very least about suspension tuning, angles, radius designs, roll-centers, and dozens of other words I can't think of right now.


What makes modern cars like the newer BMWs create a ride and handling compromise that is world renowned? Non-harsh impact over larger bumps and cracks, yet a firm, poised handling package that inspires confidence and driver enjoyment?

Any body have any serious suggestions? Not that there is much we can really do to the suspension short of changing pickup points, hub heights, etc.

Buy a BMW

at some point someone has to decide that a 32 year old car (Although the thing was designed in the early 70's) is just no longer worth trying to make contemporary.

Accept it for what it is, what are you suggesting short of altering spring and shock rates? Reengineering the suspension?

Buy a BMW, Buy a Cayman, Buy a 10 year old 911..

I thought when reading BC's post that there would be some thought provoking responses.
But Ryan Perella you did not inspire!

Allen T.
89 5 speed hybrid

You're not driving it fast enough.

The firm (spine shattering teeth falling out) ride of my SE on Sydneys roads becomes perfect once into 3 digit speeds.

expansion joints are a weak spot for 928's in terms of ride comfort-harshness..... You did mention installing larger sway bars, springs and shocks..... You mention an overly bouncy ride, which is typically due to extra stiff springs and shocks that can't keep up...with stiffer springs you need MORE rebound damping to control it...

For example, installing bilstein shocks on stock springs is a VERY nice handling-comfort combo for most 928 owners.....but when you install eibach springs on the bilsteins I have found the ride to a bit "jittery" and don't like it on the street.....HOWEVER on my race 928 I run cut (think stiffer) eibachs on bilsteins and LOVE IT....but this is a pure race car....and I do think this combo would be VERY rough on the street...

This is another good argument.....when I road in a 928 built specifically for ORR racing (the beast thats gone 209.9mph) it felt almost sluggish below 60mph....very stiff suspension...but the few times it was "in stride" it felt GREAT....

Brendan, the high-velocity impacts like what you describe are mostly the realm of the shock absorber- especially the "bouncy" part. Shocks have a number of different valving mechanisms inside to help minimize these different velocity demands- a tar strip or heave is an instant, highspeed movement of the wheel, where a small depression is a slower movement. For a shack to work on the slow speed requires a much tighter restriction then the instant, large-volume blast from a pavement edge. In most normal street shocks, this is done with a spring-loaded disc that covers a large number of holes in the piston. When you are going over undulating dips, the disc stays in place and the oil goes thru the standard holes in the piston. The sudden high velocity of a pavement edge blows the disc away from the secondary holes, allowing the suspension to compress. The resistance of this high-speed blow-off is what you feel as a hard impact inside car. How well a shock's valving is designed makes all the difference. I have seen race shocks with as many as 7 circuits EACH for compression and rebound, all adjustable individually.....if you dare....haha. This is why Motons cost a lot more than Koni's, and why shocks all seem to be different in terms of results.
I am no expert, but thats a small bit that I know about....

Steve

All of this done with stock sway bars.

Tired stock Boge Reds on stock springs: Terrible jarring over expansion strips. Lesson: tired suspensions suck.

20K mile Koni Reds in Eibachs, rebound set to full hard, 142 mm front ride height: Terrible jarring over anything and everything.

20K mile Koni Reds in Eibachs, rebound set to full soft, 160 mm front ride height: Terrible jarring over anything and everything. Lesson: Koni/Eibach to harsh for street.


New Bilsteins on stock springs: Much better but still a bit of harshness on expansion strips. Ride height from 143 to 156 to 170 dialed the harshness out significantly. Lesson: Still lacks the magic controlled, damped thud of an E92 M3 (best handling car I've ever driven thus far....)

I suppose I should put my 17" Cup 1's with PS2's on the stroker to compare with the 18" 30-series Sumitomos on it now.

Speaking as an E92 M3 owner....it did ride incredibly well given 19" wheels....handling on the street was also VERY good....and the two stage stability control was great too.....HOWEVER....on the race track it does NOT handle as good as a 928.....the M3 sits far too high and is too soft on track....so you get a weird sensation of dive-squat-roll that you don't in the 928....which is why I only drove the M3 on track once.... The M3 sits at 55" high and you sit pretty high up too...race 928's are around 46" high and in race seats you sit very low....it just feels SO much better on track

I will confess to the shame of never having tracked a 928, so hopefully someday it can be the best handling car I've ever tracked. My M3 drive was at Laguna Seca, obviously it wasn't mine, and they had us leave the traction control on, so while i was probably near my limits, the car sure wasn't. Conrad Grunewald then drove me around Laguna Seca in an E92 M3, more or less like this YT video. I have to confess I wasn't paying attention to all the nuances of the ride quality as he drifted down the Corkscrew and through Turn 9....

YOU GOTTA DRIVE ON TRACK........ If you make a road trip to norcal I'll let you drive my "Estate"......super easy to drive and just leave it in 3rd gear the whole time....don't even need to shift!!! Whats funny is you only loose a few seconds a lap in only 1 gear......

I might be going to Buttonwillow Nov 20-21, thats a bit closer to you too....you could drive in drivers school and I'll run open class.....or even drive one of your 928's.....its really not that hard on the cars your 1st few track days

My car with stock springs and Bilsteins amazes me. I've owned cars that handled well but beat you up. This combo seems perfect. I wonder if going up to 17" wheels/tires will be harsh.

I dunno, watching vintage Corvette's lap Road America as fast if not faster then their same class modern equivalents is quite inspiring :p

Did you hit your head on something????

Well, I have owned 4 928's over the last 20 years, all of them daily drivers and during that time I have had at least 5 BMW's as 'family' cars. I now have a 79 Euro and an 88s4. I love the ride on both. I rebuilt the suspension on the 79 with factory shocks and cut one coil off the front factory coils. The car rides as well as any sports car I have ever driven and handles very well. I can't say how well because I have not tracked it. If possible the s4 rides even better. The ride is a little softer but the car handles very well.

For me, the ride/handling compermise is the best I have experienced, I think it is so much better than any of the BMW's I have owned. I have had 2 325is, 1 328IC and 2 5 series (I loved them all but not as much as my sharks).

Just my 2 cents worth...

"When you increase the sway bar stiffness, and increase the spring rates, and tighten up the shocks,... "

And install short, stiff 17"/18"/19" tires...

With stock suspension, wheels and tires in good condition, they are pretty darn comfortable.