Engineering Explained: F-150 better than Cybertruck for towing duty (over distance)

[Old Spice]

This is beyond my elementary physics understanding, but here's an engineer's perspective of towing with an EV pickup versus an ICE pickup. Seems like the conclusion is that an ICE pickup has a range advantage even though it's less efficient at towing compared to an EV. But the gap will get closer as battery capacity in EVs go up.

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[Garden_Aum]

With respect to long distance towing, I do not think there is anyway to properly answer this question until after there is more information about the batteries that will be used in the production version of the truck.

 

[Saskateam]

It is interesting. I don’t think you can use the same efficiency for an ICE towing at its max weight. That assumes the F150 can tow in overdrive however it will not do this. The F150 needs to lock out overdrive to put more power to the wheels to overcome the resistance of the trailer. It is still better that an EV for towing but it does loose efficiency in the example given.

I wish they did a video that explains how much waste there is in an ICE vehicle when not towing. That same F150 driving without the trailer still has all that available energy, however does not use it and it goes out as waste heat. Yes the EV cannot tow as far but it wins for the majority of people doing the majority of their driving. Yes there are people who tow daily and need a truck to do this however most can drive an EV daily and with the money saved rent an ICE truck for the times they need to tow or plan for the longer drive time.

 

[ajdelange]

A lot of people seem to think that the CT is going to be better at towing than, for example, the X because it is somehow more efficient. Well I'm sure it is but not by much (a few percent) and efficiency really has little to do with over all towing range. Other things have a larger effect on towing range and these are the nature of the load and the terrain and the biggest factor of all: the onboard energy reservoir. A diesel truck with a 40 gallon tank running at 40% efficiency has approximately 40*0.4*37 = 592 kWh it can potentially deliver to the road to move both itself and the trailer. Making generous assumptions about the higher efficiency of the CT including regeneration we might expect the CT to be able to deliver perhaps 200 kWh, That's about 1/3 of the diesel truck's. How can we possibly expect the two to compare? If we improve the efficiency of the CT by 5% so that it can deliver 210 kWh that's still only about 1/3 of the truck,s available energy This is why I say that wrt to truck parameters it is almost entirely the battery size that is important and not so much the efficiency. Double the battery (e.g. 400 kWh total) and now the CT is about 2/3 as capable as the diesel. When the ICE manufacturers wanted to increase towing range they added bigger or auxilliary fuel tanks. Tesla would have to do the same. Rivian has a patent for such an auxiliary battery that goes in the bed. I am intrigued by the idea of an auxillary battery that goes in the trailer effectively making the trailer pull its own weight, so to speak.

If we assume that the CT will consume about 450 wH/mi in normal operation it is clear that adding a trailer than weighs (gross) about the same as the truck, has about the same cross sectional area and drag coefficient and about the same rolling resistance will also require about 450 wH/mi and will, thus, cut the range of the rig to about half of the range of the truck alone. It's that simple. No need for m*g*x*tan(grade) or any of that stuff.

 

[cybrtrk_maybe]

Bottom line... can someone estimate how far the tri-motor will be able to drive with a 14,000 lbs 5th wheel?

 

[ajdelange]

Yes, but it is going to be really crude. I'll guess that a 14,000 lb trailer is going to be about twice the weight of the truck and that, therefore, it's drag will be about 2^2/3 = 1.6 times greater and that the rolling resistance will be about twice that of the truck. Arbitrarily assigning 20% of energy requirement to the rolling resistance and the rest to drag gives (0.2*2 + 0.8*1.6) = 1.68 as the level ground estimate of the consumption factor for the trailer relative to the truck. Assuming 400 wH/mi for the trucks consumption the trailer thus needs 400*1.68 = 672 Wh/mi. Assuming range of the unburdened CT is 500 miles then the range estimate with the trailer is 500*(400/(400 + 168*400)) = 500*(1/(1 + 1.68)) = 186.6 miles and note that this does not depend on either battery size nor Wh/mi rating for the truck. Now that's on perfectly level ground. Should you undertake a 1% grade, as he does in the video, you'll need another 280 Wh/mi just to haul the 14,000 lbs up 1 mile per 100 miles but you'll also need about half again that much to haul the truck itself up there thus an extra 420 Wh/mi are required. Now you must consider CT consumption. Setting it at 400 Wh/mi (implying a 200 kWh battery for 500 mi range) implies estimated range of 500*(400/(400 + 1.68*400 + 420)) = 134 miles. ABRP has added the CT and rates the trimotor at 485 Wh/mi implying a bigger battery (242.5 kWh) and towing range on a 1% grade of 500*(485/(485 + 1.68*485 + 420 )) = 141 mi.

Change any of my assumptions and the answers will change. I hope what I did is clear enough that you could put together your own spreadsheet to play around with the numbers. I guess my takeaway here is that 14,000 lbs is a pretty big load for a truck with a fuel supply of only 200 - 250 kWh.

 

[cybrtrk_maybe]

Thank you A.J.,
Now I'm thinking that a CT will not meet my needs. There are many "hills" in Colorado going in all directions, except East, but then it's uphill heading West if you do go East.

 

[Garden_Aum]

Yes, but it is going to be really crude. I'll guess that a 14,000 lb trailer is going to be about twice the weight of the truck and that, therefore, it's drag will be about 2^2/3 = 1.6 times greater and that the rolling resistance will be about twice that of the truck. Arbitrarily assigning 20% of energy requirement to the rolling resistance and the rest to drag gives (0.2*2 + 0.8*1.6) = 1.68 as the level ground estimate of the consumption factor for the trailer relative to the truck. Assuming 400 wH/mi for the trucks consumption the trailer thus needs 400*1.68 = 672 Wh/mi. Assuming range of the unburdened CT is 500 miles then the range estimate with the trailer is 500*(400/(400 + 168*400)) = 500*(1/(1 + 1.68)) = 186.6 miles and note that this does not depend on either battery size nor Wh/mi rating for the truck. Now that's on perfectly level ground. Should you undertake a 1% grade, as he does in the video, you'll need another 280 Wh/mi just to haul the 14,000 lbs up 1 mile per 100 miles but you'll also need about half again that much to haul the truck itself up there thus an extra 420 Wh/mi are requore. Now you must consider CT consumption. Setting it at 400 Wh/mi (implying a 200 kWh battery for 500 mi range) implies estimated range of 500*(400/(400 + 1.68*400 + 420)) = 134 miles. ABRP has added the CT and rates the trimotor at 485 Wh/mi implying a bigger battery (242.5 kWh) and towing range on a 1% grade of 500*(485/(485 + 1.68*485 + 420 )) = 141 mi.

Change any of my assumptions and the answers will change. I hope what I did is clear enough that you could put together your own spreadsheet to play around with the numbers. I guess my takeaway here is that 14,000 lbs is a pretty big load for a truck with a fuel supply of only 200 - 250 kWh.

It will be interesting to see what the real world results will be. I hope they do some testing in advance of product delivery so that everyone can make an informed decision about whether the CT specifications will work for them. For those of us who will not be towing long distances, the CT is perfect even with the decrease in range while under load.

 

[ajdelange]

I think perhaps the main point is being missed. The truck must be extensively tested in order to get its EPA rating, Once we get that it is the trailer that needs to be tested, not the truck. If we know the Watt hours it takes to haul the trailer a mile we can figure out how far we can tow it given that we know the truck's Wh/mi and range. One can test a candidate trailer now especially if he has a BEV and use what he learns from that to make an informed decision.

While that's all very nice, there is, of course, no substitute for real world testing with real world trucks and real world trailers. We can only hope the people that undertake to do that will be more sophisticated than the guys who "tested" trailers with the X.

 

[Jon Snow]

No question Cybertruck will tow. With 1000 est HP & torque the only question is range. The key advantage to EVs is lower costs and longevity. Cybertruck will cut fuel costs by 2/3, will be much lower in repairs and maintenance, and will likely last 3X longer. While an ICE will likely tow a greater range .. it won’t be cheap. Decide what is important to you. If you value your money and the ability to breathe ... order a Cybertruck.

 

[ajdelange]

Now I'm thinking that a CT will not meet my needs. There are many "hills" in Colorado going in all directions, except East, but then it's uphill heading West if you do go East.

If towing a trailer that big over long distances is a major requirement then I think that the CT is not the truck you want. Keep in mind that when we see a range rating of 500 miles for the unburdened truck we immediately reduce that by 20% to a practical range of 400 miles knowing that on the road we will want to operate between 10% and 90% SOC. The same would apply with the trailer load translating the estimated level terrain load of 186 miles to 149 miles and the 1% grade estimate of 141 miles to 113.

 

[ajdelange]

Since you got me started on this there are more modest "green" trailers that use lightweight materials throughout and are aerodynamically shaped such as the f2114 (https://safaricondo.com/en/caravanes-alto/) which weighs 2356 lbs. Using the same formulas as I did for the huge trailer I estimate level towing range of 344 miles and 1% grade range of 272 mi. These are certainly more appealing numbers even when reduced by 20% (275 and 218 miles).

 

[Jon Snow]

This is beyond my elementary physics understanding, but here's an engineer's perspective of towing with an EV pickup versus an ICE pickup. Seems like the conclusion is that an ICE pickup has a range advantage even though it's less efficient at towing compared to an EV. But the gap will get closer as battery capacity in EVs go up.

The more fuel you burn (ie towing and/or if you drive a lot) .. the more money you save using an EV. Simple.

 

[Keeney]

Yes, but it is going to be really crude. I'll guess that a 14,000 lb trailer is going to be about twice the weight of the truck and that, therefore, it's drag will be about 2^2/3 = 1.6 times greater ...

Change any of my assumptions and the answers will change. ...

I think the air resistance of the trailer is going to be higher than that. They are typically not very aerodynamic. Just slightly better than a brick, so call it 0.9 (the cyber truck is approaching 0.3, so almost 3x the drag coefficient). If its a 5th wheel, it sits up high, and probably max width, so the combined frontal area will be like 60-80 square feet (2x the CT's 30-ish). Drag is a combination of the coefficient of drag x the area, so that puts the aerodynamic drag of the combo around 5x the CT. Air drag is the bulk of the resistance at highway speeds, so the range will be proportionately lower. I would not be surprised to see it down around 100 miles.

Air drag is proportional to speed squared, so the air drag at 75mph is going to be almost double what it is at 55mph. Keep the speed low to get better range.

 

[Garden_Aum]

The more fuel you burn (ie towing and/or if you drive a lot) .. the more money you save using an EV. Simple.

I do not know anyone who would drive at 75MPH with a trailer. That is stupid fast for towing something. I am comfortable driving at 60MPH with a trailer provide there is no cross wind. Driving at a slower speed will require less energy.
In the end, the logically conclusion is people should either consider tent camping or sleeping the in the bed of the CT.