We have a look at the humble leaf spring and ask whether it deserves universal scorn.
I’ve always been a suspension snob, especially on the subject of leaf springs, normally referred to by fellow scorners as cart-springs. And indeed, the use of something that you’d have found on a one horse power medieval cart on a 150mph Ferrari still seems as wrong to me today as it did when I was a picky kid and first realised what lurked under those exotic red bodies..
The first car I ever ‘owned’ was a Ford Prefect E93A that I used to drive as a 14 year old around a bit of woodland. Even at the 20 mph maximum it was possible to achieve weaving around all the trees, I still managed to turn it onto its side, a tribute to my recklessness, a high centre of gravity and its very, very basic suspension which stretched back to the Model T, comprising a beam axle at the front and a live axle at the rear, both mounted on transverse leaves.
In its most basic form, as propagated by the penny pinching Henry Ford, the transverse leaf spring’s character resembles a blancmange (does anyone still eat blancmanges?) or a jelly. The outer ends are clamped to a solid axle and the car wobbles around fixed to the apex at the centre. When mounted longitudinally, the leaf spring’s basic character still resembles a blancmange, albeit an upturned one. The axle is clamped to the middle and allowed to twist and shift back and forth with every movement of the springs.
Used this way, the semi-elliptic spring is allowed to contribute to the location of the suspension as well as its actual springiness. This is obviously a hugely compromised situation, which can only be addressed partially by the use of locating arms and, that staple of better-behaved live axles, the effective but aesthetically inelegant Panhard Rod.
On first look, the suspension of the 1961 Lancia Flavia and 1963 Lancia Fulvia seems just a step forward from the Prefect’s, yet the latter was a car that won rallies. Of course the differences are huge. First of all, although employing a transverse spring, the front wheels are independent. This wasn’t the first time this system was used.
In the 1930s, Leslie Ballamy offered an independent front suspension conversion for Fords and other cars, by the rather simple means of cutting the beam axle in half and hinging it whilst retaining the transverse spring. Jean Bugatti also produced a prototype independent front for the Type 57 using a similar, but doubtless more sophisticated, solution, but his conservative father vetoed it.
Dante Giacosa used a low mounted transverse leaf for the front suspension of his small rear-engined Fiats. I don’t believe that the prototype Bugatti still exists, the Fiat system worked well, but it was a very light car, and I’m certain that the resulting behaviour of the Ballamy system was nothing like as fine as that of the two Lancias. At the rear, the Lancia axle used two longitudinal springs, well-established practice with a solid axle on anything but the most basic car by then, even if it was a Ford, but as with the front, attention to the quality and location was all.
The 1959 Triumph Herald had adopted a rather simple independent rear using a transverse spring and swing axles but, in 1963, the Chevrolet Corvette C2 went a step further, using a transverse leaf with a lower control arm and trailing rod independent rear end and, on the 1984 C4 Corvette, the previous conventional coil sprung independent front end was also replaced by a leaf spring arrangement to complement the rear, and GM have stuck with that arrangement to this day.
Because of this, the Vette still seems to be viewed by the wilfully ignorant as a throwback to the arcane world of old Detroit iron, and is often dismissed with the kneejerk criticism of ‘still using cartsprings’. But this is a lazy and superficial comment, the way the Corvette’s transverse spring works is actually rather elegant.
The centre section is firmly located to the frame, sitting discreetly below the wishbones, meaning that the two halves virtually work as two separate springs, just as two coils would. But the fact that they actually remain interconnected means that some stiffening is transmitted from one side to the other giving the leaf inherent anti-roll qualities. From 1981, the construction of the springs has been in a lightweight composite plastic which, combined with their position, means that the whole centre of mass of the suspension is kept low.
The composite construction of a Corvette’s spring is undoubtedly more expensive than a couple of off-the shelf coils. Also, marketing must constantly rail at Chevrolet’s engineers every time they see pejorative references to leaf springs in reviews so, if the engineers resist, they must have good reason.
Their main downside is being able to offer a range of adjustability. In fact, until the relatively recent advent of switchable settings, few people ever wanted or expected to be able to adjust the settings of their car’s springs for road use but, for racing, some people replace Corvette leaves with coil-over units, but this is no condemnation of the system.
The Corvette is the most high-profile and longest duration user of this system, but isn’t alone. Volvo now use a composite transverse leaf on the rear of the current XC90, its obvious advantage being the lack of intrusive coil struts, so Chevrolet’s persistence might be vindicated.