2014 Volvo 780

At 60 mph in 12th gear the engine is turning about 1,200 rpm. At 55 mph obviously it will be closer to 1,100 rpm. While the engine can handle running in this range fuel mileage drops since it is less than ideal.

 

Depends on your situation. Where are you running? What speed are you planning on running at? If you are usually grossing close to 80,000 lbs you might gear a little slower so you can keep the engine in the desired rpm range.

My last truck had 3.42 rears with a 13 speed, 11R22.5 tires and Volvo D12. That gave me 65mph @ approx. 1,330 rpms(almost the same as the new truck with the I-Shift and lp 22.5 tires.) My typical gross is 55,000 lbs or less. Occasionally I'll gross over 60,000 lbs. and rarely over 70,000. With the higher average gross weight @ 65 mph I would gear slower if it was me(3.55-3.58 rears.)

 

My 2013 is 232wb and I wish it was shorter. I have the 5th wheel as far forward as I can get it, at 79k I'm 13k on my steer, and I still have a fairly large gap. If I had a 12k steer, it would be larger, not good for fuel mileage.

If you know what the pin is set at on the trailer(s) you haul, your dealer should be able to tell you what wheel base will give you the smallest gap for better fuel mileage.
Definetly get the 13200 steer and definetly get the I shift. I love mine.
D13 455hp, Eco torque, direct drive, depending where you run what gears you should get.
My .02.

 

Mine isn't the direct drive, and I have 346's. only seems like 6-700 rpm between 11-12 shift.
mine is always consistent in how it shifts and I rarely think "that could be done differently".
You may need yours reprogrammed? If its doing wonky things.

 

At the risk of repeating myself, GET the 13200 steer axel, and keep it as short as you can to keep the gap small. Mine is 232 and I wish it was shorter.

 

I've got a '12 780. Has a 228" wheelbase which is equivalent to a 245" non set back axle. 18 speed, 3:55 rears. 1300 gives me 65 mph. Dual 150 gals, a 36" slider set so that you can put it 6" behind center or run it up as far as landing gear or fairings allow. This is my second one I've spec'd like this and it is short enough to ride nice and it will turn into itself if you let it.