A leaf spring is a long, flat, thin, and flexible piece of spring steel or composite material that resists bending. The basic principles of leaf spring design and assembly are relatively simple, and leafs have been used in various capacities since medieval times. Most heavy duty vehicles today use two sets of leaf springs per solid axle, mounted perpendicularly to support the weight of the vehicle. This system requires that each leaf set act as both a spring and a horizontally stable link. Because leaf sets lack rigidity, such a dual-role is only suited for applications where load-bearing capability is more important than precision in suspension response.
All six generations of the Corvette have used leaf springs in some capacity. The basic arrangement for each generation is listed as follows:
In the C2 and subsequent generations, a leaf spring is mounted transversely in the chassis and used in conjunction with several independent suspension designs. Common to these post-C1 Corvettes, the leaf acts only as a spring, and not a suspension arm or a link. Because it is not required to stabilize the wheels, the leaf functions in much the same manner as a coil spring. This configuration obviates the drawbacks and imprecision associated with traditional Hotchkiss (non-transverse leaf spring) suspensions.
Although commonly referred to as a "leaf spring suspension" it is more accurately calls an independent double A-arm suspension.
The following images show the movements of an independent suspension using a transverse leaf spring. For all images:
Illustrations #1 and #2 show independent left and right leaf springs mounted rigidly to a chassis. In the first illustration, the suspension is at rest. As a left wheel moves up in the second illustration, the left spring flexes upward, but the right spring remains unaffected. Because the two springs are not connected, the movement of one wheel has no effect on the spring rate of the opposite wheel. While the C2, C3, and C4 Corvettes used a continuous spring instead of the split spring of the illustration, left and right spring rates remained independent because the spring was rigidly mounted at its center to the chassis.
Illustrations #3 and #4 show an independent suspension with a single transverse leaf spring, an arrangement similar to that used on the C5 and C6 Corvettes, and the front of the C4 Corvette. While at rest in illustration #3, the leaf forms a symmetric arc between the left and right sides of the suspension. Under the compression of both wheels in illustration #4, the widely-spaced chassis mounts allow the spring to pivot; the ends of the spring flex upward and the center moves down.
The extent to which a leaf spring acts as an anti-roll bar bar is determined by the way it is mounted. The fundamentals of this explanation appear in the Michael Lamm link at the end of this article, as well as in several patents. US Patent #6189904 is of particular relevance.
A single, loose center mount would cause the spring to pivot about the center axis, and push one wheel down as the other was compressed upward. This is exactly opposite an anti-roll bar, and has not been used on any generation of the Corvette.
A single, perfectly rigid center mount that held a small center section of the spring flat against the frame would isolate one side of the spring from the other. No roll or anti-roll effect would appear. The rear spring of the C2, C3, and C4 has this type of mount, which effectively divides the spring in two. It becomes a quarter-elliptic spring.
The C2 and C3 Corvettes from 1963 until 1983 used a rear transverse leaf spring with a central rigid mount. The spring was constructed of multiple steel leafs with plastic anti-friction liners and closely-spaced mounts. These traits prevented it from acting as an anti-roll bar.
Since the C4, the Corvette has had widely-spaced double mounts on the front. The rear spring has had double mounts since the C5. The spring is allowed to pivot about these two points. When only one wheel is compressed as in illustration #5, the portion of the spring between the mounts assumes an "S" shape, bending in two directions. As a result, the spring force applied to the right suspension arm is reduced as the left side compresses, like an anti-roll bar. The caster, camber, toe-in, and general orientation of the left wheel remain unchanged.
This anti-roll effect is the result of the compound bend, the "S-bend", that the spring must make when the wheels are not level. A compound bend requires the spring to assume a tighter bend radius. The tighter bend radius requires more force than a larger one thus greater force must be applied to the spring.
When both wheels are level the force applied by the spring to the suspension is even between the sides.
When only one side of the suspension is compressed, the leaf spring is forced into an "S-bend" shape. This results in a compound bend in the spring, as opposed to the single bend in the case when the wheels are even. The compound bend has the effect of increasing the stiffness of the spring on the side which is being compressed. At the same time, the bend reduces the force on the side which is not compressed.
This transfer of force from one side to the other is exactly the same way an traditional anti-roll bar functions. In the case of the Corvette the effects of the anti-roll bar and leaf spring are additive. The operation of the leaf spring and anti-roll bar do not affect each other but their forces add together at the wheel. This additive property allows the Corvette engineers to use a smaller, lighter anti-roll bar as compared to using a separate left and right spring (coil or leaf).
When this system was initially in design for the C4 Corvette, the engineers had hoped that the resulting anti-roll rate would be sufficient to eliminate the need for a conventional front anti-roll bar. A supplemental anti-roll bar was ultimately implemented because sufficient roll rates could not be obtained with the anti-roll forces of the leaf spring alone. [See Michael Lamm reference]
Carroll Smith is quoted in his book, Engineer to Win
Many small European cars such as the Fiat 128, the Yugo, and the Triumph Motor Company small chassis cars (Herald, Vitesse, Spitfire, GT6) used transverse steel springs in similar fashion. The Yugo's steel spring used twin attachment points and did provide anti-roll capability.
Recent research on the design concept has been performed. In 2006 Ford Global Technologies was granted patent #7029017 for Wheel suspension for a motor vehicle with a transverse leaf spring
GM Patent #5425829 desribing a method for creating variable rate composite leaf springs. Includes background information on benefits to transverse leaf springs used with conventional suspension designs