LJK Setright on the art of suspension tuning on public roads: CAR+ archive, December 1989

Published: 11 December 1989

► LJK Setright ponders suspension tuning
► The fine art of a comfortable ride
► A classic CAR column in CAR+

A terrible lot of tommyrot has been talked, in the last couple of years, about the ‘intelligent car’. It cannot, almost by definition, have been talked by intelligent people; and the intelligence of any car adequate to satisfy the muddled expectations of any other people is not a faculty upon which I would choose to rely, thank you very much. Nor should I be happy to succumb to the hideously totalitarian impositions of such vehicle systems as the Prometheus venture aims to foist upon us, in the pretence that they will prove more intelligent than we are. Happily, not too many of the bright-brained cars proposed of late have been as mindlessly authoritarian as that; in fact, the best examples to come to light have been, if not intelligent, remarkably reasonable.

Reason and intelligence are not interdependent. You will recall the dictum that I have in mind of that keen motorist, George Bernard Shaw: the reasonable man adapts himself to the world, the unreasonable one persists in trying to adapt the world to himself. Therefore, deduced GBS, all progress depends on the unreasonable man.  

He would not have said this of vehicular progress. Our cars have, until very recently, been thoroughly unreasonable, and have forced us to be likewise. When we have suffered discomfort over bumps, we have blamed the road rather than the car, even though the road was there first. When we have sensed a lurch while cornering, we have tacked stiffer anti-roll bars into place, even though there are a negation of the very suspension we had been at such pains to develop. Worse still, instead of doing one or the other, we have done both, being given to dismal compromise whenever faced with a dilemma; compromise is as far as we go in our understanding of being reasonable. 

Suddenly, or so it seems – though the idea has been taking hold since as long ago as the Ferrari V8 was offered to us in a Lancia Thema – there is a new fashion for cars which are much more reasonable, cars which do, indeed, adapt themselves to the world. They cannot be said to have intelligent suspension, for it they had, it would be active and able to anticipate, to identify and quantify, the random brick in the road. On the contrary, these unintelligent and eminently reasonable cars show us, through their adaptive suspensions, that the development of adequate sensory perception is a necessary preliminary to an intelligence able to interpret what is sensed. 

You would not have to go back through many years’ issues to find Setright enthusing over the extraordinarily sweet ride and unexpectedly sound roadholding of the Toyota Soarer, a beautiful but only tentatively made car, whose variable-rate pneumatic springs and adjustable dampers were automatically controlled by reference to road speed and vertical accelerations. Now we have the Citroen XM, a competently and convincingly made car whose springing and damping, likewise pneumatic and variable, respond also to lateral and longitudinal accelerations and to rates and extents of displacement of steering and accelerator. 

Those few extra sensors have made an enormous difference. A new standard of ride and roadholding in uncompromised combination has been established, not by imparting intelligence to the car but by endowing it with more sense. 

In its wake, but certainly not floundering, come the cars which now have adaptive damping, even though they are bereft of the refined springing of the Citroen and the Toyota. Lesser Theme (which I take to be the proper plural of Thema, this Lancia being more Italian than Latin) and at least one version of the Dedra have very effective twin-rate damping systems, and the new Peugeot 605 follows their example, though with less success.

These are not merely economical systems: they also (as does Citroen) provide for the driver to interfere with their volition and to select and unremittingly firm damper setting – not because he can do much better than the automata, but perhaps so he can satisfy himself that what he has paid for does in fact work. 

That would never do for a Rolls-Royce owner. He would never be in any doubt that everything in his car worked well, nor would he take kindly to the idea that he should do any of the machine’s work himself. Rolls-Royce has been very properly insistent on making its adaptive damping wholly automatic and in so doing, has made it easier (in concert with improvements in wheels and tyres) to incorporate a richer variety of settings. 

The softest of these, in the 1990 Spirit and Spur, is now even softer than in the cars hitherto exported to the USA. The firmest is akin to the damping which controls the Bentley Turbo R; and the difference is enormous. In between is a medial setting (RR calls it Normal, but there is little or nothing normal about a Rolls-Royce), and the three corresponding force/velocity curves run fairly parallel in bump, quite even spaced. At 4m/sec, for instance, a front damper may present a resistance of 300, 700 or 1000N; but the differences are strongly marked in rebound, where it matters. At the same velocity, the figures are roughly 300, 1300, and 4200 – which, even for such a lot of car, is a lot of Newtons. 

It makes a lot of difference. At long overdue last, it is now possible to drive a Rolls-Royce hard and fast on a winding, undulating, bumpy country road without your heart being in your mouth. The roads upon which I verified this were the Derbyshire sort where Ferodo used to test brake-linings, and where any earlier RR would have been a liability. 

I have good cause for saying that to drive the 1990 version there (or in any of those rare places presenting similar hazards) is eminently reasonable – and since the car now has heightened senses, is as devoid of sensation as a Rolls-Royce journey should be. 

What used to be merely a desirable property for an owner has now been made an attractive proposition for a driver. I had only three criticisms of a car that it would other than exceptionally good. My seat cushion was too convex; and the new 10-speaker audio system, based inexplicably on Blaupunkt components, was so poor that I thought it quite unacceptable. 

Apparently the apparatus was selected by some electricians and vetted by some directors, but there is no reason to suppose that either group had any expertise in the subject. It reminds me of what I said earlier about the priority of senses over intelligence: electrical engineering is no more important in this context than mechanical engineering, and both should be subservient to the reasonable curiosity of educated ears. 

Making unrelated expertise relevant needs a kind of lateral thinking rare in the motor industry outside Japan. Mercedes-Benz and sometimes shows signs of it, making me wonder what its adaptive damping system will be like when it becomes an option (why not standard, for goodness’ sake?) in the UK, as it already is in Germany, on the new SL roadsters.

Like RR, Mercedes-Benz has chosen three-stage damping; I wonder if it will similarly insist on the damping being entirely automatic? The German car has a fine four-speed automatic transmission, that the RR has not, but the German engineers offer one of the best means for inhibiting it. Will that reasoning spread into the suspension department? Will the unreasonable SL driver persist in expecting the reasonable car to adapt itself to him? 

By LJK Setright

Thinker, aesthete, engineering evangelist, our most celebrated contributor over three decades