Hmmm..... traction.
I don't see how they would be practical. They would have to be considerably more mechanically complex and even worse heavier.
The other thing is this a solution to a non problem? Think about it. Bicycles have large wheels. Generally, large wheels offer good traction. Have you ever even heard of an all wheel drive tractor? Tractors have such big honking drive wheels that they don't need all wheel drive and tractors do pretty well in rough terrain and muddy fields.
you are kidding right?
people were installing "front wheel assist" systems in tractors in the 50s, and manufactures started in the 60s:
in the 80s it became popular.
in the 90s it became the "norm" for large tractors
now even small tractors feature "front wheel assist"
