It's fascinating reading these posts, and from regular Club contributors who seem to know their stuff. People's views vary so much! I now have FSDs and Weitec -30s on the front of my SE 75, and modified (pre-compressed) A2 'luxury' springs on the back giving -20 net front and rear. I ran standard SE rear springs before but the ride height was too high at the rear (but not by much). The ride is the best I've achieved yet, but still far from impressive. The FSD rebound is poorly controlled on the front (a problem identified by others). In layman's terms, the front end is 'bouncy' on certain surfaces. On balance I would still fit FSDs, but in my experience they are far from brilliant. I hear what Alan and others say about their use with standard springs (which is what they were designed to be used with), but the ride height on standard springs just looked all wrong to me, so I've tried to reduce it. This is particularly important (in my view) with 17" wheels which look daft if there's too much gap around them.
Interestingly, perhaps the biggest single improvement I have made is fitting OZ Superleggera GT alloys (17" 7s with 205/40s). Previously, with 16" SE wheels (185 Pirellis) and the FSDs fitted with the -30 Weitecs on the front, the car drove without any real feel. It was a muddle. Putting the OZs on (with Fulda tyres) made a huge difference. Suddenly the car 'came together' and felt much sharper. The relatively inexpensive tyres are noisy, but the reduced unsprung weight and 'feel' has transformed the car. And far more than I was expecting.
I also think its important to 'run in' the FSDs. 2000 miles of 'settling' really does make a difference. Why I don't know. But in my experience it does. The 'bouncyness' just reduced.
I've spent so much on fiddling about with springs now that I'm tempted to leave well alone but I'd still like to find a set up which will reduce the side-to-side wobble and front bounce while maintaining a nice ride-height. ABT might do it or H&R - both non-linear progressive springs. But every time I pull them all off I have to have the 4-wheel alignment redone. It's just silly. And I'd like to try pre-compressing the front Weitecs by -10mm (as Schnelletrecker advised), but that might make the bounce factor worse. You can go on and on...!
At the end of the day, I firmly believe you have to develop your own car accordingly to your own tastes. All springs are manufactured differently, and FSD batches vary a lot too. I just wish my girl's bog-standard new Polo didn't ride so much better than my A2 which now owes me £1600 in suspension R&D. And I still haven't got it right! Mad!
I hope this helps somehow!
Richard