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Questions related to towing power

buckbuck

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I am looking for someone to solve some questions I have related to torque. I have decided to buy a F 150 Lightning all electric pickup and want to know how it would compare to my 2010 Expedition. The Expedition does every thing I ask of it. I may settle for the lower kw battery in the Lightning. I always hear people referencing the torque of electric vehicles but never mention the torque applied at the ground, especially that of a gas powered truck.
The torque listed for the Lightning is 775 ft lbs.
The torque from my 5.4 liter engine is 365 ft lbs @ 3600 rpm.
Coming off the line with the boat, I typically will run up to about 2600 rpm through the first gear ratio of 4.17:1 and then through the rear axle of 3.31 and then to P275/55R20 wheels.
So how much torque am I applying to the ground? How does that compare to the Lightning?
Perhaps the item I am getting to is what benefit does 426 hp 775 ft lbs torque (Lightning) give me compared to 310 hp 365 ft lbs torque (Expedition)?
Do I actually need that much power to tow?
Is there reason to step up to the 563 hp 775 ft lbs torque Lightning?
 

FSH 210 Sport

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I am looking for someone to solve some questions I have related to torque. I have decided to buy a F 150 Lightning all electric pickup and want to know how it would compare to my 2010 Expedition. The Expedition does every thing I ask of it. I may settle for the lower kw battery in the Lightning. I always hear people referencing the torque of electric vehicles but never mention the torque applied at the ground, especially that of a gas powered truck.
The torque listed for the Lightning is 775 ft lbs.
The torque from my 5.4 liter engine is 365 ft lbs @ 3600 rpm.
Coming off the line with the boat, I typically will run up to about 2600 rpm through the first gear ratio of 4.17:1 and then through the rear axle of 3.31 and then to P275/55R20 wheels.
So how much torque am I applying to the ground? How does that compare to the Lightning?
Perhaps the item I am getting to is what benefit does 426 hp 775 ft lbs torque (Lightning) give me compared to 310 hp 365 ft lbs torque (Expedition)?
Do I actually need that much power to tow?
Is there reason to step up to the 563 hp 775 ft lbs torque Lightning?
Typically there 7-10% parasitic losses due to the transference of power through the transmission and differential in a drive train from the engine to the rear wheels.
 

2kwik4u

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A quick note to begin. You apply torque to the axle, that torque is decomposed into a force at a distance when it leaves the axle and is applied to the ground. GM made an exceptionally clear video on how this works back in 1936. Have a look if you're interested.


Now, on to fun maths :D :D I don't have the torque curve from your Expedition and can't find consensus online. Also, I don't have the final drive ratio for the lightnings gearbox. have to make a couple assumptions to get there from here. I'm fairly certain there is a gearbox in the lightning. It's most likely a single speed non-shiftable unit, but you gain both torque and positional control by adding a gearbox to an electric motor. You also need to at least have a differential in there if you're running one "axle" with one motor. I'm going to negate driveline losses here, as well as other frictional factors, just to simplify things. The torque convertor in your Expedition helps you, but the traditional clutch style transmission hurts. Lightning has none of that mess, but still has rolling resistance in bearings and tires to deal with. I'm going to skip estimating all that, as it's not going to be a considerable contribution to the math and will only muddy the waters here.

So lets say your Expedition develops 75% of peak torque at 2600rpm (this is optimistic for a n/a engine, but we'll roll with it), through your 4.17:1 first gear and 3.31:1 final drive ratios. This is an overall ratio of 13.81:1 BTW) You're applying ~3,778 ft*lbf to the rear axle. Working off tire diameter of 31.9in (2.66 ft) and radius of 1.33ft you're applying a FORCE at the contact patch of ~1,421 per tire (~2,843lbf divided by 2 tires assuming you're in RWD mode).

Now, we'll assume that we have an AC Synchronous motor being operated in a "constant torque" mode, so you have all 775ft-lbs available through the entire rev range in the lightning. I'm unsure this is how it's being operated, however I think it's a safe assumption based on synchronous motor controls. Lets also assume that the Lightning has a 9:1 gearbox (the Tesla Model X has a 9.34:1) in front of that motor. You're generating ~6,975 ft-lbs to the axle, or about ~1,311 lbf per tire (~5,244lbf divided by 4 tires). We divide by four here as I'm unsure of the split of front to rear power on the lightning.

You can see the lightning is capable of developing considerably (~85% more) more torque, and subsequent pull force, during the retrieval stage.

With all that said you won't develop that much torque from either. You won't require full throttle to pull the boat from the water, so if your Expedition does it now, your new Lightning should do it just fine as well. You'll only develop as much torque (by limiting throttle position) as is required to pull the boat. You're likely only needing to develop a few hundred pounds of pull, maybe 1k lbs at the high end to get the boat up the ramp and out of the water. Neither will require full power from the driveline to retrieve. Likewise if you aren't 100% throttle when taking off from a stoplight, you aren't developing peak torque in either, and it's largely a non-issue.

SO......to answer your question. You don't need as much as you have now if you're just worried about retrieving. You'll notice the extra power during acceleration, merging, pulling out in traffic, passing on two lane roads, and general feeling of working the higher power vehicle "easier" than the lower powered vehicle. Something else you will notice in the lightning is the broader range of torque available. The torque curve on that 5.4 is most likely a "mountain" shape, it builds as revs build to a point, and then drops back down later in the rev range. The lightnings torque curve is flat. That is to say it can develop that full 775ft-lbs at any point it chooses in the rev range. In either, you move the curve vertically by changing the throttle position, allowing either more fuel or more electrons to flow.

I'll leave the range discussion for that other thread. We've hashed that through a number of times.

Let me know if you want an explanation of the math. I design electric drives for industrial equipment fairly often, and do this stuff all the time. Plus it's fun :D :D
 

Julian

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2kwik4u

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SO......according to this article


There are two different HP levels, but only 1 torque level. Not sure how they're accomplishing that since HP is defined as the torque delivered per unit time. Perhaps one has 2wd and the other is AWD, so you still get the same torque output, but have an additional motor delivering the same level. be curious how that is.

Keep in mind, kW is analogous to HP, however kWhr is analogous to gallons of fuel. A larger storage of energy will not yield a stronger/faster driveline.
 

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@2kwik4u Wow, thank you many times over.
First, I love the GM video. Dumbs it down for me to easily grasp. I wonder how many hotties would know how to use a 3 speed today.

All Lightnings will be AWD. They have a motor for the front and one for the back. Only difference I can see is the battery capacity.
Since there are 2 motors are they each applying 6975 lbs to their axles?

The smaller battery has a range of 230 miles and tow rating of 7,700 lbs.
The larger battery has a range of 300 miles and tow rating of 10,000 lbs.
I have decided I am either getting the base 'Pro' model ($40,000) or the top of line 'Platinum' ($90,000).
Seems like the Pro model would have plenty of capacity for me but I really like heated/cooled leather seats and other amenities.

Your explanation leads me to another question. Why do I need all that torque and horsepower???? My Expedition does everything fine with much lower numbers. I would gladly trade that power for additional range from a Lightning.
 

FSH 210 Sport

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@2kwik4u Wow, thank you many times over.
First, I love the GM video. Dumbs it down for me to easily grasp. I wonder how many hotties would know how to use a 3 speed today.

All Lightnings will be AWD. They have a motor for the front and one for the back. Only difference I can see is the battery capacity.
Since there are 2 motors are they each applying 6975 lbs to their axles?

The smaller battery has a range of 230 miles and tow rating of 7,700 lbs.
The larger battery has a range of 300 miles and tow rating of 10,000 lbs.
I have decided I am either getting the base 'Pro' model ($40,000) or the top of line 'Platinum' ($90,000).
Seems like the Pro model would have plenty of capacity for me but I really like heated/cooled leather seats and other amenities.

Your explanation leads me to another question. Why do I need all that torque and horsepower???? My Expedition does everything fine with much lower numbers. I would gladly trade that power for additional range from a Lightning.
Overkill is underrated !

Best wait and see what electricity prices are in the spring. With fuel costs set to skyrocket, it is possible that gasoline will be the cheaper route.
 

2kwik4u

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I'll take this piece by piece.
@2kwik4u Wow, thank you many times over.
First, I love the GM video. Dumbs it down for me to easily grasp. I wonder how many hotties would know how to use a 3 speed today.
Glad you liked the video. I've seen it help really solidify the premise of a force at a distance for many people. The idea that gears are just big levels wrapped around a cylinder is hard to describe in words.

All Lightnings will be AWD. They have a motor for the front and one for the back. Only difference I can see is the battery capacity.
Since there are 2 motors are they each applying 6975 lbs to their axles?
I would assume that the 775ft*lbf that Ford quotes is the TOTAL amount. I think it would be safe to assume that either axle can provide up to 50% of that at any given moment. It's possible that the torque rating is limited more by current draw from the batteries than what the motor can produce. In that case software will dictate which motor creates more torque at any given instant to ensure that current draw is not exceeded. If this is the case it opens some really neat opportunities to "balance" the forces from each axle. This can change the driving dynamics from AWD, to FWD, to RWD depending on any number of variables.

The smaller battery has a range of 230 miles and tow rating of 7,700 lbs.
The larger battery has a range of 300 miles and tow rating of 10,000 lbs.
I have decided I am either getting the base 'Pro' model ($40,000) or the top of line 'Platinum' ($90,000).
Seems like the Pro model would have plenty of capacity for me but I really like heated/cooled leather seats and other amenities.
I love my heated and cooled seats. Seems like the Platinum is the way to go for that alone. With that said, assuming they are testing to SAE J2807 (the industry towing standard), most likely current draw from the smaller battery is capped, which in turn caps maximum torque available, and finally slows overall acceleration, leading to lower tow ratings. Since the towing standard directly measures acceleration, it's likely the cause of the lower tow rating on the smaller pack. Often times however, at least in ICE powered vehicles, tow ratings are dictated more so by cooling capacity than by available torque/power. Part of the standard requires a pull up the Davis Dam Grade, at speed, and without overheating. I doubt that is the case here since the larger pack will most definitely generate more heat.

Again, assuming Ford is playing by the standard here, you can read through that standard to get an idea of what really goes into your tow ratings. here's a good article from 2015.

Also, have a look at the GVWR (Gross Vehicle Weight Rating). This is the total amount of weight the truck/trailer/cargo/passengers can safely weigh. 7k towing probably indicates a 12k or 13k GVWR, which leaves very tight margins for gear, fuel, food, coolers, etc in the truck. It's worth a check if you want to dive that deep.

Your explanation leads me to another question. Why do I need all that torque and horsepower???? My Expedition does everything fine with much lower numbers. I would gladly trade that power for additional range from a Lightning.
Short answer is; You don't. It's sure nice to have, and makes life easy when you no longer have to decide if you're going to merge before or after that semi in the near lane as you enter the interstate. Just because you have that capability, doesn't mean you're constantly using it.

Keep in mind torque (and by relation HP) is a "DRAW" style system. You will not produce a single ft*lbf more torque than is required to move the load or to break traction. You will simply accelerate faster until you reach the capacity of the prime mover (ICE, or Electric motor) at that instant. If you don't have your foot buried to the floor, you aren't using 100% of available power. You are only using some smaller percentage of that. Think of it like a semi truck towing my 190. Just because it's capable of making 1,500ft*lbf of torque doesn't mean it'll use it all. I will only generate as much as it needs to accelerate at the given rate.....OR, juts accelerate faster. Take that same semi, and put 60k lbs of trailer behind it and you need a lot higher percentage of available torque to accelerate at the same rate. i.e. you're foot's further in the throttle.

In terms of an EV, you will only use what you HAVE to use to generate a given acceleration. The Rivian for example uses ~400Whr/mi when cruising around empty. A Tesla Model 3 will only use ~200Whr/mi at that same speed. Towing with a Model X I've seen reports as high as 1,200Whr/mi when towing a large camper with lots of frontal area, a headwind, and highway speeds. SO, if your new Lightning takes say 550Whr/mi to tow your 21ft jet at 70mph on the expressway.....then well, take that figure and divide it out by capacity and there's your towing range.

The EV's keep quoting capacity in "miles" and that doesn't do any of us any favors when comparing to an ICE. Even worse, Miles per gallon is a stupid measure of efficiency because it's non-linear (that is to say a 5mpg increase from 10-15 is 50%, but a 5mpg increase from 50-55 is only a 10% increase). We should really be using gallons/100mi. That is a much better set of units to use, despite hardly anyone in the US being familiar with that setup (it is on the Monroney sticker though)......Point being, compare your towing energy usage to your stated capacity and you're get an idea of how far you can REALLY go on a charge. I would wager that ~550Whr/mi is pretty close for a pickup towing a boat at speed.

in case you couldn't tell, I love this stuff. Let me know what else I can help with :D
 

2kwik4u

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Overkill is underrated !

Best wait and see what electricity prices are in the spring. With fuel costs set to skyrocket, it is possible that gasoline will be the cheaper route.
I just did this math for a Rivian last week.

It really depends on what you pay for electricity. I'm fortunate that the first 750Kwhr is $0.10/per and only $0.07/per after that in my area. NorCal might not be so fortunate. I assumed 15mpg for an ICE fullsize pickup, and $3.75/gal for gasoline. The whole thing will be very location dependent.

Here's how the math worked out. We can shuffle some costs around, but these are pretty good estimates for the Southeast area of the US.

1633900040434.png <--Click to enlarge

$0.625/Kwhr cost gives us a break even condition over the life of the vehicle.
1633900185376.png <--Click to enlarge
 

FSH 210 Sport

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I just did this math for a Rivian last week.

It really depends on what you pay for electricity. I'm fortunate that the first 750Kwhr is $0.10/per and only $0.07/per after that in my area. NorCal might not be so fortunate. I assumed 15mpg for an ICE fullsize pickup, and $3.75/gal for gasoline. The whole thing will be very location dependent.

Here's how the math worked out. We can shuffle some costs around, but these are pretty good estimates for the Southeast area of the US.

View attachment 165036 <--Click to enlarge

$0.625/Kwhr cost gives us a break even condition over the life of the vehicle.
View attachment 165037 <--Click to enlarge
Dude that is some awesome math you worked out! Great job!

Where I live, time of use metering during peak time is $9.45 per KWh! Crazy right? That’s 9,450 MIL energy. I thought that was far fetched then I remembered what the MIL energy was a few years back in ca during peak times and it was $5 per KWh, or $5000 MIL energy. That $5K MIL energy was when natural gas was going for $7 per MMBTU. Projections are going to be double that during the winter months…. We shall see what happens in the near future.

I don’t want to hijack this thread for a different discussion, but again awesome job on the mathematical breakdown!
 

buckbuck

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I would wager that ~550Whr/mi is pretty close for a pickup towing a boat at speed.
Fortunately the Lightning will have built in ongoing calculations displayed with data from a variety of inputs. It will be interesting to see how close you are on your numbers.
Since I do not deny the accusation of driving like an old lady, I am going to believe I could get at least 50% of the range while towing.

I do not recall seeing any GVWR numbers but I know that I have come close with my Expedition. And the Lightning is going to be heavier. I will have to keep an eye on that information when it becomes available.

@FSH 210 Sport Did you mean to say you electricity cost is about $0.945 per KWh.
Our cost here in IL is about $0.10 KWh.
 

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I could've swore I saw the pro model only has 5700 lbs of towing capacity, could be wrong. I was heavily looking at them for a bit
 
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2kwik4u

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Fortunately the Lightning will have built in ongoing calculations displayed with data from a variety of inputs. It will be interesting to see how close you are on your numbers.
Since I do not deny the accusation of driving like an old lady, I am going to believe I could get at least 50% of the range while towing.

I do not recall seeing any GVWR numbers but I know that I have come close with my Expedition. And the Lightning is going to be heavier. I will have to keep an eye on that information when it becomes available.

@FSH 210 Sport Did you mean to say you electricity cost is about $0.945 per KWh.
Our cost here in IL is about $0.10 KWh.
Speed is a much larger indicator of energy usage than weight. Especially when towing due to the significantly increased aerodynamic drag created by trailers. Flat front trailer like RV's, and cargo trailers take a larger hit than boats in that regard. Keep in mind that aerodynamic draw increases with the square of velocity. Double your speed and quadruple your drag, regardless of shape.

Also, I sure hope @FSH 210 Sport meant $0.945/KWh.......$9.45/KWh seems excessively high!
 

FSH 210 Sport

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Speed is a much larger indicator of energy usage than weight. Especially when towing due to the significantly increased aerodynamic drag created by trailers. Flat front trailer like RV's, and cargo trailers take a larger hit than boats in that regard. Keep in mind that aerodynamic draw increases with the square of velocity. Double your speed and quadruple your drag, regardless of shape.

Also, I sure hope @FSH 210 Sport meant $0.945/KWh.......$9.45/KWh seems excessively high!
It is $9.45 per kWh during peak time. I thought it was a misprint at First and had to ask the utility for clarification. Otherwise the rate during non peak is 7.5c per kWh.
 

2kwik4u

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It is $9.45 per kWh during peak time. I thought it was a misprint at First and had to ask the utility for clarification. Otherwise the rate during non peak is 7.5c per kWh.
I guess that's one way to curb demand at peak times. I'll tell ya right now I would have damn near everything in the house in a timer in short order.

How do the meters work out there for them to know not only how much, but when you pull power from the grid?
 

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Almost $10 for a kWh??? It'd be fred flintstone in my house.
 

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*Currently @2kwik4u in this thread* haha!
1634043088724.png
 

2kwik4u

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@buckbuck @Acard7

Here's some more neat math. I think you can realistically expect somewhere in the low 200mi range with a Long Range Lightning towing a 21ft Yamaha. Of course things like travel speed, and anything you can do to help aerodynamics (bed cover+boat cover+ no tower) will decrease that usage number.

1634048667452.png

It's really interesting to see how much more efficient the EV is at converting energy to motion. The Lightning only misses the ICE range estimate by 32 miles (12% less), but used ~81% less energy overall. It's really quite impressive from an engineering standpoint to get that increase in efficiency by switching prime movers.
 
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