Some small outfit is offering plans for a toy (model?) heavy duty
lowboy. You can see the project at:
http://www.woodcollectortoys.com/
(I have nothing to do with this toy designer!)

But on a forum based woodworking site,
http://www.woodworkingcrafts.com/forums/
two question have come up:

1. What is the name of the part of the tractor trailer setup that adds
extra axles and wheels between the neck of the lowboy, and the 5th wheel
of the truck's tractor? It looks like 8 extra tires to assist weight
distribution.

2. What is the purpose of the two wheels and an axle at the top of the
detachable neck?

--My wild guess has to do with low ground clearance of the lowboy, and
maybe the two wheels would act like a sacrificial tires to keep the
lowboy's neck from getting bent or damaged by uneven ground at the job
site, or they could be just spare tires for the rig. (Wow, wouldn't it
be a Bit** if at a job site the neck got damaged and the load couldn't be
unloaded.)

Hopefully someone here was once a heavy duty rig driver.

Thanks In Advance.