[Munchskull]

The reason that you would not see a four wheel drivetrain that often is because it has a large scrub force compared to many other options in drive trains.

Scrub forces is determined by how far apart the front and back wheels are. I don't know the equations but the smaller length your drive base has the less scrub force and the more manuverable it is.

It is because of scrub force that teams will use 6 wheel drop center. Wheen the middle wheel is lower than the rest it effectively gives you a drive base that behaves like it is half the lenght when it comes to performance but has all the stability of the full length.

If you have any more questions feel free to PM me and I will help as much as I can. I had a longer post I was going to submit but my phone deleted it.