Diesel Pusher upgrading to heavier toad-advice needed

[JBouknight]

Hello. I am a long time lurker and have always gotten the information I need from searches. Having trouble with making a decision and would like some advice from some persons who have done this or the reverse.
We have our third Class A which is a 41' 2006 American Tradition with a 400HP CAT rated at 15,000 tow. I have been towing a 2013 F150 Crew Platinum. Now I have a 2018 RAM 2500 Crew. The new truck should be about 2000 pounds heavier. How much difference is making the 2500 our TOAD going to make in power and fuel?
Thank you

[pigman1]

Interesting. Do we have any thermodynamics trained individuals out there who might comment on this. When I went through my engineering thermo courses it seems to me that the overall power (efficiency) of ANY heat engine (gas, diesel, turbine, etc.) was always higher as the temperature spread between engine operating temp and outside air temp increased. In plane language higher efficiency as it got colder out there.

As far as the airplane example was concerned, the reduction in payload was caused by a reduction in density altitude at takeoff. That could have effected the airplane two ways. Either the runway was too short and the reduced engine efficiency did not allow a the heavy plane to accelerate to takeoff speed before you ran out of pavement, or the takeoff speed needed to be higher due to less dense air caused by the heat and airport altitude, and you were still in danger of running out of pavement. Each aircraft has performance diagrams that tell the pilots (or commercial airlines dispatcher) how the aircraft is going to perform with a given load, temperature, and density altitude.

[wolfe10]

JBouknight wrote:


I don't know about everyone else but after reading that, I am going to have all of these calculations going on in my head while driving down the road.LOL The newest of which is the cold air temp robbing my MPGs. :E
Thanks for the interesting info!

Aerodynamic drag changing with temperature should come as a big surprise. More molecules to "hit" at colder temperatures.

I KNOW pilots know this. Heck, this summer we just flew non-stop Dallas to Sidney, Australia. Airbus 380. Sold out flight. 1/4 seats EMPTY. With hot temperature in Dallas, not enough lift (not enough air molecules passing over/under the wings) with full plane (ya and enough fuel for the 17+ hour flight).

Our MPG in summer running the dash air is still better than freezing temperatures trips without the compressor running.

[JBouknight]

wolfe10 wrote:
Bottom line (based on physics):

Extra weight has little effect on flat ground once up to speed.

Extra weight makes a difference when accelerating.

Extra weight makes a more significant difference when climbing grades.

Go to this link and download the PDF. Written by Caterpillar Corp, but same physics applies to all vehicles.

***Link Removed***

I don't know about everyone else but after reading that, I am going to have all of these calculations going on in my head while driving down the road.LOL The newest of which is the cold air temp robbing my MPGs. :E
Thanks for the interesting info!

[Alan_Hepburn]

We burn gas, not diesel, but we recently switched from towing an 1800 lb smart car to a 4400 lb Jeep Wrangler. Out average fuel mileage went from just under 7 mpg to just over 6 mpg...

[Executive45]

wolfe10 wrote:
Bottom line (based on physics):/snip/



http://forum.dieselrvclub.org/index.php/topic,6594.0.html

Interesting read, Brett, thanks.....Dennis

[Ed_C]

We tow a 4800 lb Jeep, a 5500 lb Sierra or the Sierra with a golf cart and lots of other stuff at around 7000 lb; there is no big difference.

[wolfe10]

Bottom line (based on physics):

Extra weight has little effect on flat ground once up to speed.

Extra weight makes a difference when accelerating.

Extra weight makes a more significant difference when climbing grades.

Go to this link and download the PDF. Written by Caterpillar Corp, but same physics applies to all vehicles.

http://forum.dieselrvclub.org/index.php/topic,6594.0.html

[JBouknight]

Great information! Thank everyone for your replies.

[CA_Traveler]

Upgrading from our 3,200 lb CRV to the 5,450 Jeep we could detect the additional drag during acceleration. And grades a little more so.

Our fuel consumption went from 8.0 to 7.8. Very difficult to determine if this change was from the increased weight and/or other variables. 60-62 MPH 400 ISL

[ferndaleflyer]

you will see the difference on the hills. No matter if its in the slip stream, and has little friction you still have to "lift" it to go up hill. Still shouldn't make much over all difference.

[WAFlowers]

If you think about it there is almost no wind resistance with the toad riding in the slipstream of your RV. I say almost because the air does swirl coming off the roof. And there is almost no rolling resistance (bearing and other driveline friction) but, of course, there is a little.

Where you will see increased consumption, if you had really good (laboratory) instrumentation is during acceleration. But that only lasts a short while compared to just rolling down the highway.

Based on my experience you will see more fuel impact from a windy day than from a heavier towed vehicle. So relax and enjoy! 🙂

[pigman1]

If you see it at all, it'll probably be very slight. We always pull the Silverado and most of the time it's empty or close to empty, but when we head to Alaska (9 times so far) the truck goes about 8100 lb. Most times I'll see a tenth or 2 on my bus mileage, but sometimes nothing.