F450 vs Ram 3500 DRW tow vehicle
So the wife and I are moving to the full time RV lifestyle. We just purchased a 42' toy hauler this weekend, with a GVWR of 20K#. Now I'm looking at a tow vehicles. I'm considering either purchasing a...
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I think many people believe that only rpm effects fuel efficiency which is true if the load is the same at all rpms, but that isn't the case when the load on the engine is different especially when you add different gear ratios into the mix.
Basically, you need torque to move the wheels and to counteract the forces pulling you back. You increase torque two ways, more engine load(fuel) or gear multiplication. A torque converter also increases torque, but that is essentially gear multiplication in hydrophilic form.
Keep in mind, that load does not necessarily mean rpm increase. An engine at 1,800 rpm can make partial, half or the max amount of power it can possibly make at that rpm depending on the amount of load(fuel being injected) is being placed upon it. The more power you need.want to make at that rpm requires more fuel since it is more of load being placed on the engine.
Anything you tow requires a certain amount of torque(force) to counter act the forces that want to pull you back. The amount of force wanting to pull you back is always changing even when the weight stays the same such as going up/down hills or high drag scenarios. Basically, you must have enough torque to overcome these forces in order to perform the work at a certain speed(aka make horsepower). If you don't have enough torque then your truck will keep downshifting to greater torque multiplication and more engine torque until it has enough torque to overcome this and make horsepower.
So getting back to the fuel thing. Say you are pulling a trailer that is pulling you back with 1,200 lb-ft of force. You can can easily pull this load in 5th at 1,900 rpm or 6th gear at 1,600 rpm. Even though 5th puts you at a higher rpm, it has greater torque multiplication and more of the torque needed to overcome this 1,200 lb-ft is coming from this gear torque multiplication rather than adding more load to the engine. In 6th gear, even though it is turning at less rpm, the truck has less torque multiplication and therefor more load(more fuel) is placed on the engine to make up the torque needed to overcome this 1,200 lb-ft of force pulling you back. Basically, you are planting your foot to the floor in 6th to get full load/max effort out of the engine and half throttle or half load in 5th so you are not needing max effort at that rpm from the engine in 5th therefor less fuel is needed.
When there is very little force pulling you back and it takes very little effort or load from the engine to overcome this force, then 6th gear is the optimal choice for fuel efficiency. All this applies to different rear gear ratios as well.
Basically, you need torque to move the wheels and to counteract the forces pulling you back. You increase torque two ways, more engine load(fuel) or gear multiplication. A torque converter also increases torque, but that is essentially gear multiplication in hydrophilic form.
Keep in mind, that load does not necessarily mean rpm increase. An engine at 1,800 rpm can make partial, half or the max amount of power it can possibly make at that rpm depending on the amount of load(fuel being injected) is being placed upon it. The more power you need.want to make at that rpm requires more fuel since it is more of load being placed on the engine.
Anything you tow requires a certain amount of torque(force) to counter act the forces that want to pull you back. The amount of force wanting to pull you back is always changing even when the weight stays the same such as going up/down hills or high drag scenarios. Basically, you must have enough torque to overcome these forces in order to perform the work at a certain speed(aka make horsepower). If you don't have enough torque then your truck will keep downshifting to greater torque multiplication and more engine torque until it has enough torque to overcome this and make horsepower.
So getting back to the fuel thing. Say you are pulling a trailer that is pulling you back with 1,200 lb-ft of force. You can can easily pull this load in 5th at 1,900 rpm or 6th gear at 1,600 rpm. Even though 5th puts you at a higher rpm, it has greater torque multiplication and more of the torque needed to overcome this 1,200 lb-ft is coming from this gear torque multiplication rather than adding more load to the engine. In 6th gear, even though it is turning at less rpm, the truck has less torque multiplication and therefor more load(more fuel) is placed on the engine to make up the torque needed to overcome this 1,200 lb-ft of force pulling you back. Basically, you are planting your foot to the floor in 6th to get full load/max effort out of the engine and half throttle or half load in 5th so you are not needing max effort at that rpm from the engine in 5th therefor less fuel is needed.
When there is very little force pulling you back and it takes very little effort or load from the engine to overcome this force, then 6th gear is the optimal choice for fuel efficiency. All this applies to different rear gear ratios as well.
