gear ratio/axle weight

I would run 4.10's and Super 40's which give you heavier geras with the light housings.

 

How much weight is on the rears with all those axles? I would think 40's would be fine.

 

Whatever you choose, running in direct gear will give you the best performance and lowest fuel consumption, since you mentioned mpg, and you will putting more of your power at the wheels. Overdrive gears will reduce actual power to the wheels. I am not talking about getting out of the hole here. But the roads you primarily run, at the speed you normally run, and the best operating range of your engine. You want all of that coming together in a direct drive. For what you want to do, that is an 18 speed running in 16th gear. Will give all the splits into the basement for starting. You will be happier overall than trying to spec to run in overdrive. I know a couple of serious heavy haulers that spec their truck to operate primarily in direct drive when they are at their normal pulling speed. You won't get eat up so bad on those small hills and overpasses. Of course, the top two holes would be essentially worthless. Keep in mind, that when a truck is put on the dyno to see what the engine is really doing, they test it in direct drive. More of the power is making it to the wheels in direct drive. Input and output shafts are essentially linked up and you are not wasting power turning a bunch of gears. That still gives you 16 gears to play with and good deep reduction in the bottom.

I would look at axle housing as well. Most axles have a 9.5mm axle housing. An 11mm axle housing would be better doing what you are. I just put in a truck order and it will have 11mm aluminum axle housings. Lighter than steel, yet will not flex. They are offered in 40K and 46K ratings. The 46K variety will offer larger gear ring.

 

32,000lbs is the limit in Mi for a multi axle so technically a 40,000 lb axle is fine. It's the torque of pulling 160,000 lbs in soft terrain that breaks parts. Back in the day most ran 46's in heavy work but nowadays most run super 40's with full lockers. On a modern truck with 22.5 rubber I'd run 3.90 with an 18 spd. Pulling Mi trans fuel mileage is going to be bad regardless. I think you'll be doing good to get 5 mpg average.

 

I had a T800 Pulling lowbeds for 7 years with Super 40's 4.10 rqtio and an 18 Speed RTLO18918B where I'd gross up to 200,000 lbs and went off road to pipeline projects such as this picture of me hauling a Cat 589 Sideboom. I was actually grossing 188,500 in the pic with the 589. Not 186,500 as stated.


www.hankstruckpictures.com/pipex.htm