OK, dumb question here, But I assume you are talking just rear springs here?
If I fit uprated springs on the front then I may as well fit shocks there as well as it will all have to come off?
So how would the car feel with springs changed on the rear and shocks and springs on the front?
Ok, I had an lsc chassis set up as you describe there, and this then highlighted sl limitations... or "an annoyance" with the back.
I found the problem, such as it was, is a feeling of lack of independence on each side from the rear. As if(I don't know for sure)hitting a bump on one side of the rear would force some air out of that side and into the other. Like the air line linking the two shocks can't transfer the air quick enough, like a delayed reaction pumping up the other side. Or, like it should have independent air lines. Rather than a tee off to each side as they actually have...
I pointed this rear suspension issue out to 2woody when he was in the car and he referred to it as porpoising. A term I'd never herd of. But I describe it as a "goodness gracious me" head action when driving. Side to side as the rear of car rolls around the diff centre point. The back seems to roll like a boat, rather than absorb bumps per side.
The front simply didn't have the problem, and the the roll action didnt start until the rear wheels hit the same bumps the front dealt with no problem at all.
Conclude, reluctantly, bin SL.
Or, as I sit In front of telly... Self leveling, your fired!

I never got round to changing Sl shocks on my previous car which had lsc rear springs and lsc front shocks and springs. But on this car, having found lsc to be a tad too soft "for me", I fitted irmscher springs all round with B4,s on the front only, and keeping SL on the rear. Same but more exaggerated result, as the difference in performance was even more marked. Back was still wobbling around. Fitted B4's on the back as well, pulled the SL relay and the difference in quality is marked. Far more compliant with the rear now matching the controlled feeling of the front. No more wobble from the back, any more than the front anyway. Independent corners. Laaarvly.
Once set up, I then fitted my sport stars with lower profile tyres, and I must confess I was concerned the ride would be too crashy, ESP over broken and potholed surfaces, and considered taking them off in favor of the 17's as standard.
However, after a couple of months the set up has settled in beautifully, the ride is now compliant, and supple but with no increase in body roll. On the way home tonight I drove down a load of country lanes with potholes and bumps on single track roads, no problem at all.
Now you might suspect I'd got used to it, and I did too. But a certain admin agreed, I believe, that his second trip from the passenger seat was much improved over his initial test drive down the a33 saying ooh it's a bit firm.(it certainly was) it's now perfect, the 18" sport stars are staying. Phew! 8-)
So pleased. But what's supple but firm for me, may be to firm for others. Having followed you though, I suspect you'll agree.

Down side? Fully loaded the car is quite low at the rear(it's never grounded) camber increases slightly and the back moves around a little more than I would like. However I haven't had the back set up again since adding the lpg tank in the boot. So there may be room for improvement on that front.
The car is rarely fully loaded, so sl is staying off. [smiley=2vrolijk_08.gif]
