Why do you Cummins guys want more gears
I’ve heard a number of Cummins fans saying they are waiting for an 8 or 10 speed transmission before getting a new truck. Why? Does the Cummins struggle to get your trailer moving from a stop? Or are ...
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4x4ord wrote:Devo the dog wrote:4x4ord wrote:
The ideal rpm range for the Cummins to be at towing a typical 15k fiver down a flat section of highway at 65 mph is between 1500 and 1700 rpm. I think 3:31 gears would work excellent.
Why at a lower RPM instead of at the peak torque?
The 2021 Cummins makes 1075 lbft of torque @1800 rpm. If you were going to work it at 70% engine load it would be very efficient at 1800 rpm. At 70% engine load it would be making about 260 hp. It would also be burning about 12 gallons of fuel per hour. If you were towing at 65 mph while burning 12 gallons per hour you’d be getting 5.3 mpg. Even at 50% engine load it might be quite efficient but even 50% load at 65 mph works out to 7.5 mpg. I’m guessing the Cummins would get more like 10 mpg towing a typical 15 k rv down the highway at 65 mph. Under light load conditions like that it will get a little better fuel economy at lower rpm as well as provide a nicer quieter towing experience.
I tow a lightweight 5th wheel and set the cruise control to the speed limit. It's 37', has a low roof height and only weighs about 9000 when loaded up. Outside of California where the speed limits are higher, I'll set the cruise control to 70 to 72. We typically get between 10 - 11 mpg. When we were in California, I set the cruise to a speed close to the required 55 and the fuel mileage was only in the low 11's.
The nice part about it is that it's quiet. The only downside are all the other issues I've had. So, I'm in the process of getting rid of it. Heck, Ram hasn't been able to perform the latest recall work, even though I've had two dealership visits, both of which were scheduled appointments weeks in advance. LOL. The funniest part is that Ram keeps on emailing me, and calling me, telling me that I need to get the recall done. HaHa. FCA is a really messed up manufacture.
That aside, I get about 9 mpg towing the same 5th wheel with my 2005 F350 V10. But, I only tow at about 60-62 mph, and it slows down going up hills. So, the road trips take a bit longer and it's no where near as quiet. But at least the heater, AC and radio works reliably, along with the rest of the truck.
