What is up with the questions about gearing?

Pretty much all of the 12 speed auto shifts have the same gearing as the upper gears on a 15 speed, with the 15 having a few extra lower gears.
So no, they are not closer spacing.

 

Rawze agrees, thinks down speeding is hard on the liners, causing them to eventually frett, shake themselves loose wearing the seat.

 

You mean like driving at lower speeds?

 

I'll take that with a grain of salt please. I hardly use high gear. I try to keep my 12.7l 16-1700rpm cruising unless empty and very light.

It will take along time for the Aero electronic trucks to convince me that I need to upgrade. My 20 year old set up as in fuel economy and reliability to me has not been surpassed with all the stuff they have added.

 

Great advise! Not understanding your costs is a surefire way to make boat loads of money. You are definitely ready to become O/O

 

No, driving slow is fine. He doesn't like the ultra low rpm gearing. Running engines 1200 rpm ish all the time, or lower. Prefers above 1350 rpm, even up to 1600 rpm cruising speed.

 

I does not matter what your costs are. When you are leasing a truck for $1 per mile ball park you never will make money unless your fuel costs you $1 per gallon than that may help a little. Mile pay should have died a long time ago.

 

All you dubs need is a 13L or a 11L and an auto trans with a 2.xx rear gear. 22.5 rubber

 

Auto trans can go in the trash.

 

You just triggered a thought in my random memory by describing the way you drive your series 60.
That's exactly where I found that those engines liked to live, from about 1550 to 1700 rpm seemed to be the sweet spot.

I'm really impressed, (kudos to you), that you have a going home gear that you don't feel you need to use all the time, triggering another thought.

The possibility of having 2 or 3 gears to choose from to keep the engine in the power band at 65 mph, (the golden number), and in the economy rpm range between 1200 and 1500 rpm.

While piddling around with a road speed calculator I found that 3:08's on 24.5 rubber with an 18 spd would give you the ability to do this, run 65 mph in direct gear at 1500 to 1600 rpm, leaving you with 2 OD gears at .81 and .73 to choose from in any given situation, light, heavy, head wind, tail wind, running M/T, probably not so much uphill, but downhill for sure.