[luckyu]

Sorry, I lost track of this thread. My bad!

Originally Posted by DaanBMW

OK, so you are riding on the bumpstop to begin with ?

Yes, in front. In back I can't see but I calculate I have 1/8 to 1/4 inch between shock body and jounce bumper.

The null effect of the RSB kinda makes sense then, the bumpstops are a very high-rate progressive spring on top of your actual spring so before the bar would transfer spring rate from the inner wheel to the outer your bumpstops are probably already stiffening the outer wheel suspension to virtually rigid.

You are right. The sway bar will add even more resistance to roll, but there was already enough, apparently.

Question: You said you have OEM performance springs. Why are they so low as to ride on the bumpstops ? Or should the stops have been swapped for shorter ones for these springs ?

To the best of my knowledge, this is what happened. BMW offered a kit a couple years ago, called BMW performance suspension. It included shocks plus bump stops plus rear shock mounts, and sway bar bushings. Best I can tell, this kit was designed to work with the sport suspension springs.

But back then, in our infinite wisdom, a bunch of us here on the forum decided the kit was actually designed to use the yellow bmw performance springs, and installed them. That's what I did too. The upshot is I have springs that do not match my shocks or bump stops.

The newer BMW performance suspension kit includes yellow springs, and is meant to work with those springs.

I guess a couple of clarifications are due: It's not the power out of the corner I'm mainly concerned about. What I am trying to improve is mainly the initial body movement when initiating cornering. ...

I don't like the body movement of the new cars either. But, I can't tell if you're going for lap times, or for a particular feel you want the car to have.

If you really are interested in reducing *initial* movement, then that is 99% shocks. Initial movement is allowed by (relatively) weak shocks.

Can you state your goals? Are you racing competitively, or are you trying to achieve something with your car that you *believe* will make it faster? I'm not saying you're wrong. What's your test for achieving your goal?

EDIT: OK, you stated your goals in the original post: spirited driving. I see another set of Bilsteins in your future.

... You can improve it with a very early turn-in and flattening the curve, but not all corners are the same, and when I turn more abruptly the body movement is larger then on my older Golf. Out of the corner the bimmer being a RWD it really helps a lot more to re-gain neutral steering, up to the point where you can if you want to, to break traction/adherence.

OK.

Now to my experience to date, on a FWD Golf. I put in Bilstein sports + H&R sports, and no less then 3 RSB were on the car (not planned, but had to... long story). W/o the RSB the cornering was way worse, even with the upgraded suspension, but for sure it was miles from stock. The reason an RSB is way better then a v. stiff suspension is that it acts only when you need it, i.e. during cornering, and not all the time, thus it won't make the overall ride too harsh.

Aha, so you care about ride comfort! Good to know...

Other then the RWD dynamic which is clearly different between the Golf and the bimmer, I would think the net effect of the RSB would be similar. The other rear bits would reduce the suspension movements increasing the precision in cornering and overall.

You didn't mention what the RSB effect was. What the M3 RSB does in my mind is it makes the car neutral steer, increasing max mechanical grip. That's what the numbers say (but they don't include the effect of bump stops). I'm talking about high G steady state turns here.

Something to think about: no matter how soft or stiff your springs are, spring resistance at static is 800 lbs per corner. The softest spring you can imagine will still have 800 lbs initial resistance. Same for sway bars, although they ramp up faster. Initial resistance is zero. The thing that will actually control initial body movement is shocks.