Why no Hydraulic Drive Systems on roadcars?

[KASCII]

In a farm situation I have operated both conventional and hydrostatic driven machinery. From my experience a hydrostatic drive, although it has its pluses such as near infinite speed selection, is very hard of fuel (required a larger engine). Almost 110%-115% greater fuel use than conventional drive. Depending on job being done.

But the machinery I'm thinking of is from the late 1990's. I know that the earlier designs were even more inefficient, in the 120% worse range. But in certain farm applications, where you need precise speed control, hydrostatic drive is a huge bonus.

In farm machinery applications, a speed range is gear selected. The engine speed can vary, but is normally fixed at a specific speed, to prevent lugging the engine or stressing the hydrostatic pumps and motors. The speed variation is obtained by adjusting the fluid volume flow. I wouldn't know if operation and performance is different on newer equipment though.

[Sixbarboost]

The viscous losses would be massive even at city-speeds and on the highway absolutely terrible.

But it works perfectly on the mining equipment I have worked with, but they don't move so fast.

[Facts Only]

One of the large yellow goods manufacturers conducted a long interanl study into the fuel efficiency of traditional transmission drive vs hydrostatic drive and found that a traditional transmission is more efficient and the gap is widening with improving transmission technology.
Hydrostatic can offer better packaging but these days a gearbox offers more capabilty as well.

[Zynerji]

Great read for a post that has spanned 7 years!

Great question OP! Answered a few questions that have been rattling around in my head for years!