Theme: Suspension – It’s A Kind Of Magic

The suspension system is where the car comes into contact with the road and tries to a) keep it there and b) pretend as if the road doesn’t exist. That’s a lot to ask…

1983 Peugeot 604. Image: www.lrm-collection.fr
1983 Peugeot 604. Image: http://www.lrm-collection.fr

…and then get precious little thanks in return from customers or indeed motoring journalists. The former probably don’t know what suspension is. The latter want all suspension to do the same thing, namely to keep fast cars stuck on the tarmac at 145 mph. This conflict is as big as the one facing the suspension itself, which must mediate between the undulating road and the dynamic system that is the car in motion. The other circle to be squared is that of ride comfort versus handling.

1992 Buick Roadmaster
1992 Buick Roadmaster

Taking all this into account, the suspension system is the least well-understood part of the car. You can see the body, inside and out. That’s easy to comprehend. The engine is a controlled mass of moving parts, all tightly interlocked and with the degrees of movement and rates of motion firmly constrained within narrowly defined ranges. All that has to do is move the car as quickly as possible. You can see it work and judge action and reaction. The suspension can’t be so easily assessed nor its behaviour second-guessed even by those rare souls interested in its activities. In a way its role is to negate.

Life is easier for the orchestrators of motive forces than for the suspension wizards. To a large extent, the engine specialist has total control over the inputs: that’s the accelerator pedal. The oxygen content and temperature of the air can be allowed for and the vehicle’s weight and payload are predictable. The engine is essentially a closed system, as simple as a railway network. Not so the suspension.

1976 Citroen CX green without line

The suspension engineer is not able to constrain the inputs, only define limits of operation with variables of potentially infinite values. The suspension engineer must define requirements of handling and comfort in relation to that mass of unknowns known as a road surface and even whatever tyres the car is eventually fitted with. The required output is that under normal use the car must be comfortable and secure. At the same time, when the car reaches the limits of grip, it must fail in a progressive and secure fashion. Failure must be predictable and gradual so that the driver can learn the limits of the car’s ability. And the manner of failure must be accounted for. There is a major difference between progressive understeer and snap oversteer.

Differentiating the chassis engineer from the others is that the science of suspension is largely empirical and related very firmly to subjective perceptions. Whereas an engine can be computer-modelled to a very high degree, the chassis can’t. The differences between the predictions made by a mathematical simulation and the reality of an engine’s performance are two orders of magnitude less than those between a mathemetical model of a suspension system and its actual behaviour.

Rover 75 Before

The chassis and suspension engineer must select a set-up which, at best, can only approximate to the one required. Then they need to test it on a track and public roads to determine which elements need adjustment. To do this she or he must understand in principle how the elements work and then, in practice, judge how to vary them to get a result which satisfies the perceptions of an unknown group of human users. I refuse to call this an art but it is certainly an unusual blend of engineering and imaginative empathy.

Image via favcars
Image via favcars

The other imaginative part is to conceive of how an unknown group of users will want their car to feel. Companies such as Rover, Jaguar, Lancia, Citroen and Peugeot have been very good at producing cars with a good ride and handling compromise. Personally, I feel that ride is more important than handling. One can always drive more slowly but one can’t make a rumbly, harsh ride less so once the suspension engineer has decided the specification. I notice that most of the cars on my roll-call are either out of business or have abandoned any pretence at good taste in the ride department. Only Jaguar keeps the flame alive and I am quite confident the Leamington Spa chapter of the Jaguar XJ-6 club will tell me the new cars are no match for the ill-shaped rust-traps they champion so vocally.

And we have not even got as far as discussing sprung mass, friction, damping and roll velocities.

Author: richard herriott

I like anchovies. I dislike post-war town planning.

9 thoughts on “Theme: Suspension – It’s A Kind Of Magic”

  1. Thought provoking stuff, but as you say once the suspension keeps the tyres pressed firmly to the ground everything else is subjective. Common sense might agree with you – ride being more important than handling but the market seems to feel the stiffer the better. Stiffened and shortened suspension is always sold as better and premium. P.s. That Buick is truly an awful looking car!

  2. I like that slightly overstyled look of the Roadmaster and the contemporary Caprice. A successful marriage of old American full-size glory and modern (at that time) design language.

    But back to suspensions: whoever rides in my C6 will comment on how quiet and smooth it wafts along, but few would notice when I set the suspension on “sport”. After admiring those qualities they exit and buy their next car with shortened sports springs and bone-hard seats, not without complaining about their ever aching backs.

  3. A very thoughtful and thought-provoking piece, thanks.

    I wonder if excellent in “body control” is the holy grail these days, particularly on less well surfaced countries? Whilst I have grown to love the way a oleo-pneumatic car creates isolation from most road surfaces, my experience is that a) sharp ruts catch it out, and, b) there are types of road and times of the day when I’d prefer to have less isolation from what’s going on. So, a more firmly controlled car can be more relaxing that a more isolated one (if anyone can point me at a firmly controlled, well isolated car then I’ll probably go and buy it).

    To bring my point to life, I once owned a FIAT Cinquecento Sporting which had a short wheelbase and knobbly, yet well controlled ride, and was quite noisy on the motorway. And yet I found it more relaxing to drive than the “more refined” Honda Integra (EX16 – with the pop-up headlights) that it replaced, because the latter never felt properly tied down (lovely engine and gear-box, though).

    1. The suspension on our 2016 model Passat with fancy pants electro-trickery enhanced suspension is pretty good. It copes well in the twisties, is comfortable over poor surfaces, even the sort of ridges that tend to catch out oleo-pneumatics and copes admirably well with speed bumps (though nowhere near as well as my Dyane!). Not magic carpet good, but way better than many (overly) firmly sprung modern vehicles. You never get that feeling of detachment that you can get in something like a DS.

      Over back country undulating roads with as many patch repairs as original seal, I always found the properly suspended Citroens to be supremely able and comfortable, making for fast and relaxed progress.

    2. Fast driving in an old school Citroen is never a problem, if you are on your own. The driver never really notices unfashionable body roll. The problem is that other drivers and passengers do.

      When I had a Dyane, I know that its behaviour looked scary to outsiders (and admittedly some insiders) even though I knew it was perfectly safe. And that was when people knew what body roll was – even Formula 1 cars rolled back then.

      Nowadays excessive body roll must look quite alien.

  4. The likes of Clarkson’s Top Gear on the telly have sold everybody into the handling-over-ride nonsense.. People want racetrack-bred low profile tyres on enormous rims to impress the neighbours and put up with an awful harsh ride on real patched-up roads.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.