Vertical volute spring suspension



Vertical volute spring suspension is a type of vehicle suspension. It was chiefly used on US (and Italian) armoured fighting vehicles from the 1930s to after the end of the Second World War.

Development
During the 1930s, many innovations in the components of light tanks would make US tanks considerably reliable. These included rubber-bushed tracks, rear mounted radial engines and the vertical volute spring suspension.

A volute spring is a compression spring in the form of a cone (a volute). Under compression the coils slide over each other, affording longer travel. The result is more stable and powerful than any leaf, coil, or torsion bar spring in the same volume. Mounted vertically in a road wheel bogie for a pair of road wheels in a tank made a very compact unit.

The Rock Island Arsenal produced a small tank for the cavalry which used vertical volute spring suspension instead of leaf spring suspension. Standardized as the M1 Combat Car, it entered service with the US Army in 1937. The design was used in the M2 light tank and subsequent Stuart tank series. Design features of the Stuart were scaled up for use in the first M2 medium tanks which would evolve into the more successful M3 Lee and M4 Sherman, all using the VVSS.

Replacement
Battle experience showed a relatively short life of the original vertical volute spring suspension (VVSS) of the late models M3s due to the tank's increasing combat weight with larger guns and larger tracks. After mid-1944, M4A3 models of the Sherman adopted a newly developed Horizontal Volute Spring Suspension (HVSS). This type of suspension involved springing the pair of dual road wheels on each bogie against each other with a volute spring. When the horizontal volute springs were placed in compression by either the front or rear bogie wheel arm, the load was transmitted to the opposite arm. This kept tension on the track. Compared to the vertical volute spring suspension which it replaced on the US M4 Sherman, HVSS was heavier, but stronger, allowed the changing of individual wheels, and increased wheel travel.

When fitted with the HVSS suspension the tanks were known as the M4A3E8 model - and soon gained the nickname 'Easy Eight' since they were more comfortable to travel in than models with the previous VVSS suspension, due to the extended track/wheel travel.