GT6 Suspension


Like all Triumph Herald derivatives (Herald, Vitesse, Spitfire & GT6), the GT6 has fully independent suspension on all four wheels. There are various types of independent suspension systems:

1. Macpherson Strut.
2. Double Wishbone with coil or torsion bar springs.
3. Multi-link.
4. Training arm.
5. Twin i-Beam.
6. Moulton.
7. Transverse leaf spring.
8. Hydropneumatic.

The GT6 has Double Wishbones with coil springs at the front, and a transverse leaf spring at the back.

Front Suspension

This is by double wishbones and coil springs, where two wishbone shaped arms are connected from the chassis to the front hub assembly, or trunnion. The wishbones arms can be solid, but in the case of the Triumph, the upper arms are split into 2 although each part cannot operate independently of the other (see green highlighted areas in the parts diagram below). The shock absorber is mounted inside the coil spring, both of which are located on the lower wishbone and the chassis.

The wishbones can be seen clearly in the photo below (together with their chassis mounting points and bolts):

Front suspension by wishbones came out in the 1930s, pioneers including Citroen and Packard (who advertised it as a safetly feature). The revolutionary Citroen Traction Avant of 1934 had front suspension using wishbones and torsion bars (like a spring, but straight) see below:

The Standard 8/10 and all TR sports cars all have wishbone front suspension. The Herald derived front suspension has been used on a variety of other cars and kit cars including the Caterham (for which some modified parts are offered by Canley Classics).

Rear Suspension

The rear suspension uses a transverse leaf spring and swing axles.

Sometimes referred to as 'semi-elliptical' or 'cart springs', a typical leaf spring is made up of a cross-section of rectangular cut spring steel 'leaves' which are bent and fixed together to form an arc shape. The majority of leaf springs have a longest leaf or 'main leaf' where the ends are heated and rolled to form circular shapes called 'eyes'. These eyes allow the spring to connect to the vehicle body while the centre of the spring allows location to the axle. Normally below the main leaf are a number of leaves which are usually progressively shorter, however in the case of the small chassis Triumphs, the shortest leaf is at the top. A leaf spring can be made up of a single leaf or over 20 leaves depending on the application.

Swing axles are a British invention, by an Edmund Rumpler in 1903. Their principal advantages are each wheel is independently sprung, and a reduction in unsprung weight since the differential is mounted to the chassis (i.e. is no longer part of the suspension). Their most recent use includes Volkswagens up to 1967, the Mercedes 300SL, Porsche 356, Tatras, Chevrolet Corvair, as well as the Triumphs. The principal drawback to this type of suspension is well known : that there is an extreme amount of camber change from bump to droop and that this can cause "jacking" under extreme cornering (see below)

As can be seen the tyre contact area becomes minimal with a consequent loss of grip (it happened to me many years ago in my Triumph Herald which 'spun'. Fortunately for me at the time there was no other traffic or I may well have hit something!). Many engineering solutions have been devised to this problem. Triumph came up with two:

1. The The "swing spring" pivoted the transverse rear spring on the differential, so that the body could roll more than the suspension, without impairing the ride in a straight line.
2. A fully controlled rear axle, with a lower wishbone (reversed) and a rubber coupling or doughnut (Rotoflex) at the outer end of the drive shaft, but that was no longer a swing axle.

1. Above is used in the later GT6 Mk3 as well as the Spitfire Mk4/1500. 2. Above is used in the Mk2 and early Mk3 GT6. Please refer to the Rotoflex section of this website for details of this rubber coupling.