Frank did you read this? "Yea, I was thinking more about my next
truck." I thought he was considering a new rig, but you can put
those things on any age truck you want.

I understand.  I like considering options myself.  I have a friend with
a Ford Powerstroke, 4.11 gears and the 6sp manual.  To put a US gear
type addtional overdrive/underdrive behind the whole thing would make it
a really flexible set up.  But I've never used their product so I'm only
dreaming a bit.

To do it right you'd want to get a gearging chart spreadsheet going and
think through carefully the engine rpms at given speeds in given gears.  
That can be fun when you're in the mood for it.

You could logically assume that the larger tires would both weigh more
and hold that weight further from the axle.  That combination would
store more energy as kinetic energy like adding flywheel weight.  It
would require more torque to accelerate the tire rotation, but once up
to speed the power requirements would be only dependent on the
frictional losses in the bearings, oils, air resistance, etc.  So you
would only see a change in acceleration not power consumed driving down
the road.  These considerations are taken into account with light weight
wheels and tires as used on race cars, but I doubt they would be
noticeable on a pickup truck and trailer combination.  Certainly not
zero.

I'm not sure about the brakes.  They would probably require some
additional pedal effort (probably not noticeable) to overcome the
additional leverage of the larger diameter tires, but the amount of
energy required to be absorbed and dissipated by the rotor will remain
that of the kinetic energy of the vehicle.  So fade problems should not
be increased.

I see where "Chris Cowles" <NoSpam@For.me> contributed:

Not zero - and can be important with extreme size change (imitating
Bigfoot).   But within normal wheel wells it is not a Big Deal.

Will Sill
The Curmudgeon of Sill Hill