Gear ratio over drive or direct for heavy haul up to 110K?

Do you have no plans of ever going any heavier than you do? I ask because it seems to be inevitable, everyone seems to want to go bigger.

 

Good luck with that. Even with 4.30’s some of these hills have down to 12th. One particular hill in Pennsylvania with 136 on I was down in 5th. That’s with an 18spd 515 Cummins 1850 torque

 

Winner^^^^^^^ as six would say !

 

Thank you @Oxbow and @superhauler ,
Sure took a long time to get to the primary reason, imo.
Now can someone enlighten me about the 5yr warranty coverage of a twisted drive line or stripped pinon in a heavy haul application?
Bought mine new and dealer specifically told me damage like that “was not covered”.
@Rontonio ?
Just askin

 

Can he put you in touch with someone running this setup with these weights?

 

I don't know the technical aspects of the DT12 specifically but in most cases (using the typical Eaton Roadranger as an example) direct drive is usually stronger than overdrive since power goes straight through the box, rather than off the input gear, to the countershafts and then onto the mainshaft. I'm willing to bet the reason they don't recommend the direct drive for over 80k lbs is because the rear axle ratio needs to be taller in order to give you a reasonable top speed. That taller rear ratio now ruins your startability and you run the risk of trashing your powertrain trying to get that heavy weight moving.

 

Something I don't quite understand here- please correct me if I'm wrong.

I always thought that the big advantage of a direct transmission is that when you run it in direct you escape the parasitic power losses associated with having any extra gears meshing. That advantage is only present in whichever gear is a direct 1 to 1 ratio. Even in a direct transmission all the other gears will have a parasitic loss.

In a heavy haul application, how much time do you spend in high gear? Especially in the mountains?

 

My concern isn’t pulling it’s launching, a 2:64 isn’t going to launch easily. You’re solely focused on cruising speed to the detriment of everything else.