Bilstein PSS9 or H&R or other ?

Lscman,


I have heard all of the discussions on ride heights, the car is not slammed to the extent you suggest. I have had the kit at all ride heights and I settled on these after a lot of experimenting.

At 320mm rear and 340mm front this is lower than std but did not show any noticeable bottoming traits ?

What are the mm measurements for stock ride heights ?

I suspect the dampers have softened over the last 15k miles, just feels softer than it used to and it has always felt softer than I would like

Tks
A

Carrera2RS said:

Ok remeasured from arch lip to wheel centre


F 343mm (averageing the two) Rear 324mm If stock is 14.5 F and rear 14.0 that sounds about right. Lowered but not slammed unless slammed is 1" or so !

Click to expand...

With 343/324mm,

Front is 13.5"
rear is 12.75"

This is still lowered a lot...perhaps not slammed in the weeds, so to speak. The E39 M & sport jounce travel is marginal to begin with. Many cars like Corvette and Honda offer 3"+ of jounce. When BMW hot-rodded the E39, they reduced jounce. They did NOT modify pickup points and key suspension parts to facilitate lowering while maintaining jounce. Your 13.5" value on the front allows about 1" of jounce travel (or less), depending upon the brand of coil-over kit. A value around 14" is better for handling & will reduce bottoming. I think a very high spring rate or progressive spring will be needed with this chosen ride height front and rear. You have basically cut the jounce travel in half from stock, so spring rates need to be at least double of stock. A spring rate under about 500lb/in will probably bottom frequently with this setup.

Cutting/shortening bumpstops is a double-edged sword as they become more unsettling when contacted. When you see 1-1/2"+ suspension excursion and touch a shortened bumpstop, the "effective spring rate" (incl the shorter bumpstop) will sharply spike upwards and induce severe understeer. This means a hard bump hit on corner entry under braking will tend to throw the car into a flat skid where the nose of the car proceeds straight ahead instead of turning in crisply. If you have 1" of suspension travel to absorb bumps AND suspension compression under braking, you're at a real disadvantage.

Keep in mind that the BMW sport suspension and M suspension takes precious jounce travel from the intended E39 design. A non-sport car rides around 15" and easily has perhaps 30% more jounce travel than an M. This allows the job#1 E39 design to soak up a 2-1/2" bump without bumpstop contact or launching the car chassis airborne, which causes loss of control. The lower the car becomes, the less forgiving the chassis becomes. At some point, famous BMW handling is absent....jounce is reduced until the suspension no longer soaks up rough pavement, aggressive maneuver, unanticipated traction loss or driver error.

Lscman,

Thanks for the pointers, I did park next to a stock M5 in Maidenhead today and as I had my tape in the car I sneaked some measurements:

F 362mm (average)
R 352mm (average)

So I guess my car is approx 1" down at the front or slightly less and just over 1" at the rear. Bouncing my rear it does feel a little soft but moves quite a lot in terms of travel.

I wish I was less aesthetically oriented ! But given it is 99% used on the road and looks great 1" lower than stock, I'm tempted to compromise a little ..... Sorry :sad1: I wish I was more purist ! Don't want to slam it but at the moment it looks luvley ....

Any thoughts on an improved setup over the Eibachs, PSS9 if I promise not to drop it too much !?

Think the feeling so far is

Eibach too raod
KW ok but less well developed than some
H&R too hard for everyday
Dinan had stage III and hated it
GC, won't deal with they were rude !
PSS9 - very good but quite track oriented ? I don't mind stiff and I'm NOT looking for Merc ride but don't want it to feel inappropriateley stiff with crash and creaks over every bump ! (That's just fine with my RS but not a full leather airconned M5, would feel wrong !)
Others ?

gsfent said:

OK, not to be facitious, but can you trim the bumpstops to get a little more room on full compression?? Or is the only alternative to raise the ride height (assuming no change in hardware). Rick??
Regards,
Jerry

Click to expand...

You can indeed trim the bumpstops about 1/2" to 3/4" to get a bit jounce travel without bumpstop contact, especially in the front. It has pros and cons....

The BMW bumpstops are huge & soft, but this is very intentional,
as it makes the handling more predictable under full excursion. The stock bumpstop raises the effective spring rate gently under abnormal conditions. A shorter bumpstop generally needs to be made of harder material. The typical "step function" you get in many cars with short, harder rubber bumpstops is what sends them headfirst into a tirewall when you brake too late in rough spots. I have driven perhaps 100 different lowered cars with streetable springs on tracks and I could feel the bumpstops firmly contacting in most cases. This bumpstop contact limits velocity and lap times. Most owners assumed it was the road surface they were "feeling" until I pointed it out with them as they sat in the passenger seat. Under these conditions, the cars will try to get out-of-shape as the instantaneous spring rates jump around and the car see-saws between understeer and oversteer. Optimally, you should never contact the bumpstops hard and the chassis should remain neutral and totally predictable. This is what a tossable car is about...one that allows sustained 4 wheel drifts with ease. The M5 suspension rates were NOT designed for severe duty street or track use. Even Ground Control 550lb springs with aggressive dampers & ride height set to about 14" is marginal for a 2 ton sedan at triple digits. Such spring rates are at home on a 3200lb M3, Vette or Mustang.

*If E39 pickup points were altered or lowering spindles were sold to mate with shortened struts, things would be very different. In these cases, optimal geometry, jounce & handling could be maintained with a superslammed car....assuming the frame didn't grind off under braking & the wheels didn't rub through the top of the inner fenders. Such products available in the aftermarket for certain marques & many race cars have these mods.

After trimming bumpstops, you should leave the car around 14" for optimal handling. If you want the car to sit lower, you are following a "function follows form" philosophy (more show with less go). "Illogical", as Spock says. Anyway, I am not compelled to follow urban styling trends or 17yo kids.