No axles behind the tandems, just a lift axle in front of the tandems or just behind them. What you're referring to with additional "rear" axles is a log trailer, that hooks up to the log truck or a tractor, and yes we have them here also. There is a difference between a truck and trailer & semi.
If its got bolsterS and picker, its a log truck, period, and specifically what it is made for. Length makes no difference, regardless of PNW or East coast.
Your including log trailer axles with the truck, and they are not included in the truck axle configuration. While you're also referring to a log "hauler" semi combo, which needs the "tractor" & trailer to haul the logs, sometimes has no picker and only one set of bolsters on the "tractor" portion of the semi, which cannot haul logs without the trailer, and many cannot be self loaded or unloaded due to no picker, and is therfore a log hauler for transport only.
A dump truck is a obviously has a dump body.
Here is a few examples of a "logging truck" & a "logging hauler".
I can post an example of a triaxle "dump" truck if you need some clarification there also?
You may want to look up the difference between a tractor & a truck also. Your referring to a logging tractor & trailer combo or semi. Dependent on each other to haul logs.
A logging truck is is self reliant, and can load, haul & unload logs without the use of a trailer, and also with the use of a trailer. But never reliant on a trailer.
A Logging tractor or semi cannot, and needs a trailer & tractor to haul at all.
Triaxle log truck
http://www.truckpaper.com/listingsdetail/detail.aspx?OHID=5259477
http://www.truckpaper.com/listingsdetail/detail.aspx?OHID=5412405
Semi log hauler
http://www.truckpaper.com/listingsdetail/detail.aspx?OHID=4949877
Semi with picker
http://www.truckpaper.com/listingsdetail/detail.aspx?OHID=5562691