rpm when towing
When towing with my ram diesel how do I tell when I should downshift. it seems to tow so easy, but slows when going uphill at 60 what should my rpm show.
Forum Discussion
4x4ord wrote:Wild Card wrote:
Thats cause the Cummins is most at home at 2100rpm. Peak torque. Everyone gets caught up in the HP craze. Horsepower doesnt do crapola for pullimg grades. Gear it for peak torque and let it pull.
Comments like this are what confuse people. Here is the math:
If you have a 2015 Cummins/Aisin it makes 865 lb ft of peak torque at 1600 rpm. If it is run through gears to slow the rear axle down to 507 rpm (5th gear with a 4.10 rear end) the torque on the rear axle will be 1600/507 x 865 or 2768 lb ft of torque.
Now rev that engine up to 2800 where it makes 385 HP and the torque drops down to 722 lb ft. Drop down to 3rd gear. Your rear axle will be turning 509 rpm. The powertrain will be able to deliver 2800/509 x 722 or 3972 lb ft of torque to the rear axle.
So in 5th it can put 2768 lb ft to the rear axle and in 3rd 3972 lb ft to the rear axle. HP is king ...... if you have HP, torque can be generated with gears.
These numbers assume no power loss through the gears and so are to demonstrate the physics rather than be absolute values.
Yep, that is why high HP gas engines, can't tow what a diesel. More energy per gallon. I will take a Low HP/High torque over a High HP/low torque gasser any day. Diesels don't need to spin fast to move a load.
