Cybertruck a towing God: Part 3 - Range (Newest Video)

[cybertrucktruckguy]

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[cybrtrk_maybe]

Good and informative video; Maybe some editing/cleanup on the last 5 minutes.

 

[ajdelange]

Towing range depends on the number of watts it takes to move the tractor and the number of watts it takes to move the trailer per mile driven. Both of those vary all over the place with towing conditions, weather, driving habits etc. The distance you go is the discharge capacity of the battery divided by the utilization rate. As we do not know what even the average utilization of the CT will be (we think it will be between 350 and 450 Wh/mi) nor the battery capacity (we think it will be between 180 and 220 kWh) but we do know the product of the two will be 500 miles - the specified range for the vehicle. And as we have no idea what the numbers for the trailers are going to be there isn't much point in trying to estimate towing range under a particular set of conditions.

We are not helpless, however. We can ponder towing one CT with another (were than an allowable thing to do). It is clear that the towed vehicle is going to require just as many watt hr to go a mile as the towing vehicle in this case and it should be clear, therefore, that the available range will be half that of the towing vehicle alone or about 250 miles for the TriMotor. We can try to extrapolate this to the general case of any vehicle that weighs about the same as a CT. Of course we don't know the weight of the CT but assuming it is going to be about 6500 lbs we conclude that a trailer weighing 6500 lbs can be towed about 250 miles and that ones weighing more can be towed less far than that and trailers weighing less can be towed farther.

One place where we can be definite with respect to towing is the power required to ascend grade. Assuming the CT to weigh 3000 kg (6600 lbs) and towing 14,000 lbs it takes an extra 25 kW to tow uphill at 60 mph per percent of grade. That's 416 Wh/mi and scales directly with grade and speed. It's pretty clear from that that adding 1% grade alone will add as much extra consumption as another CT and so, were there no other additional load, cut range in half. Better put if we assume the CT only consumption is 416 WH/mi and that we are towing something that weighs 6600 lbs which adds another 416 Wh/mi and that we are driving 100 miles during which we will increase elevation by 1 mile (1% grade) which adds another 416 Wh/mi our consumption will be 3 time 416 and our range thus cut down from 500 mi to 500/3 = 167 mi.

The physics of towing with a BEV are no different than those of towing with an ICE truck with one significant exception. Therefore you can expect the same wide variabilty in range, The distinction is that the largest loads on an ICE vehicle's power plant are the inertial and gravitational ones. These are both proportional to mass and so degradation in range largely depended on weight. In a BEV those loads become less significant because of regen and, thus, drag becomes more relatively important.

But the big question here is are these killer trucks? Omigosh yes! Elon said that we won't appreciate how good they are because we don't know enough to figure that out but perhaps he didn't realize how much just telling us the 0 - 60 performance reveals if we have a decent weight assumption. 6600 lbs seems pretty reasonable (3000 kg) and 0 to 60 in 2.9 seconds implies that the motors can deliver 27.7 kN of thrust and assuming that power limiting kicks in at 60, that the motors are capable of 744 kW, Those two facts imply performance curves that will be something like these;

The solid curves say we can expect 0 - 100 in about 5.5 sec and a quarter mile time of about 10 seconds. The broken curves are for a 14,000 pound trailer being pulled up a 10% grade. 0 - 60 in 13.5 seconds and the quarter in 20 seconds. I'm still looking for an error in my calculations because I just can't believe these numbers. When I look at the big (6.4 L) diesels I see 250 - 300 hp engines that can be blown to 600 hp. This truck has about 1000 and 14 kN-m torque at the wheels (0.5 m wheels). I don't know much about trucks. Are there diesels that can do this?

 

[Mini2nut]

You can bet the CT will be using HD wheel studs and lug nuts to handle the amazing torque. Will they go 8 lugs as well, just like 3/4 and 1 ton pickups?

 

[ajdelange]

We estimate 27.7 kN of thrust. With half meter wheels that means torque of 13.8 kN-m for half meter wheels, 4.4 kN-M per wheel. If the lug nut radius is 10 cm that means tangential force at the stud radius of 44 kN which is torque related 5.5 kN shear on each of 8 studs or 7.3 on each of 6 plus their share of the gravitational force. As I don't know what sort of load wheel studs can handle I can't say more than that.

 

[Keeney]

When I look at the big (6.4 L) diesels I see 250 - 300 hp engines that can be blown to 600 hp. This truck has about 1000 and 14 kN-m torque at the wheels (0.5 m wheels). I don't know much about trucks. Are their diesels that can do this?

In terms of making 600HP out of a Diesel, there are certainly plenty of Diesels that can make that kind of power. But the current crop of stock HD Diesel pickups are around 400 to 450 HP . They key for uphill towing is how long can you sustain the power. ICE vehicles are typically not setup with enough cooling to sustain max power output continuously without overheating.

Long ago, I used to work with some guys who wrenched on top fuel tractor pull machines. Some of those engines took up to 600HP just to spin the blower.

 

[ajdelange]

I think it's been brought up here before but the CT appears to be capable of 500 kW of power (well over 600 HP). It is going to be well over 90$ efficient but that still means 50 kW or so of heat needs to be disposed of. So while that amount of power is enough to pull a 14,000 lb trailer up a 22% grade at 75 mph you aren't going to be able to do that for very long unless the thing can dump that 50 kW overboard. That takes about 14 tons of air conditioning! Thus we can be sure that the onboard computer will limit speed when towing near max weight up a grade.

The diesel to deliver 500 kW would produce at best around 1250 kW of heat.