Quote:
Originally Posted by cRiPpLe_rOoStEr
What could go wrong?
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The problem is that the total springing in a hydrolastic/hydrogas car is a function of tyre pressure and the suspension. It's also important to note that each set (side) of wheels is linked through the suspension. When you hit a bump therefore as the front wheel rises, the pressure in the displacer pushes the rear one down. If the tyre pressure is higher than it should be you get a bouncing effect which isn't very pleasant. You don't get it on the Citroën type suspension because that isn't passive & you don't get it on conventional suspension because the wheels aren't interlinked (except on the 2cv and that's a separate case).
So if you raise the tyre pressures say to 40psi & you hit a bad road it rides something like a 1200kg kangaroo after 7 pints of Guinness. It would eventually become undrivable because the suspension would just go into a permanent oscillation (I'm not sure that's the right word). Even raising the front from 30 to 32 is marginal.
The advantages of hydrolastic are a much better ride (because of the front rear interlink) much less (read almost no) body roll (because the roll moments are countered by both wheels on one side tightening up the springing rate (effectively) and much simpler packaging because the displacers take up less space & are cheaper than, a mcpherson strut arrangement. The disadvantages are that for each application you need to use a computer to work out springing rates (horribly expensive in the 60s/70s (now you could do it on a smartphone)) and the like, so if you wanted to build a new model with hydrolastic you'd need to simulate it, work out spring rates in the displacer, fluid pressures, what rubber compound to use and the thickness of the metal parts inside supporting the membranes - as well as the bore of the interconnecting pipes. It needs to be pressurised/depressurised to be worked on (you do NOT want to make a mistake dealing with 230-245psi pressures).
The real problems nowadays are age & spares/maintenance - that said I can get mine pumped up at a garage within walking distance. Surprisingly it's not the displacers that fail, it's usually the joints of the interconnecting pipes that give up the ghost.