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Deep Dive On The Tesla Semi’s Numbers

I’m not going to lie, I’m not big on math. I did okay in high school and college in math classes, but I didn’t pursue a science, engineering, or other technical degree. So, I’m probably not the person to go to if you want a deep look at the numbers behind a clean technology. But I do know who to go to when I need those numbers, and one of those people is Jason at “Engineering Explained.”

There are a lot of people who think that Elon Musk is a bit of a con artist. Some of them short the stock, some of them just don’t like the guy, and others have made an actual case. So, whenever Tesla or SpaceX announces something new, there are always a few people trying to tell us that it’s impossible, and thus probably a scam.

This is where Jason’s skillset (an actual engineering degree) comes into play in great ways. Instead of wildly speculating, Jason decided to put claims against the Tesla Semi to the test. And, now that more numbers are out, he gave them an even deeper look. The results are often good for Tesla, but there are a couple of bad news items.

Range & Battery

He starts by covering the likely battery capacity of the Tesla Semi. He doesn’t have the exact official figure (because nobody outside of Tesla does), but some information that Tesla and Elon Musk gave out during the delivery event and on Twitter was enough for Jason to give us a very good estimate.

The good news? It’s likely that the Tesla Semi didn’t need a megawatt-hour pack. The efficiency is actually good enough that they could get away with only 850 kWh of battery cells, which saves Tesla a bunch of money, preserves the battery supply for other vehicles, and is generally better for the environment.

He also took a good look at Tesla’s 500-mile drive. One thing many viewers didn’t notice was that you could look at the drive and see the speedometer. Tesla’s estimated range of 500 miles is based on a 60 MPH speed, which is important because the vehicle didn’t use its whole battery on the drive. A closer look shows that the speeds were closer to a 55 MPH average.

This is important, because it further backs his estimate of 850 kWh. They wouldn’t need the whole pack to travel 500 miles at 55 MPH.

Of course, he proves this. He takes the drag coefficient of the vehicle, its weight, and every other factor he could get good numbers for, and comes up with a need for 800 kWh in a previous video. He recalculates this for 55 MPH, showing that you’d come in at only needing 740 kWh to pull off this run. This leaves plenty of room to only use 93% of an 850 kWh pack.

Speed

He then goes on to ask the question of what it would take to travel at a more realistic 70 MPH. From talking to truckers and my experience matching their speeds in some hypermiling experiments, most trucks go 68–70 MPH, even in Texas where they could legally go faster. Why? Because trucking companies often limit the speed to 68 to save fuel and reduce risks.

To go that speed would require about 1187 kWh, which is definitely more than the Tesla Semi has. Aside from the pretty solid case he made for an 850 kWh pack, 1187 kWh is also more than the larger 1 MWh estimate many other people have been making. If he’s right and it has an 850 kWh pack, the range at real-world speeds is more like 350 miles.

Jason then works to analyze the question of whether a 350-mile range is good or bad. As Tesla pointed out, many routes (as much as 80%) are fewer than 250 miles, so the truth is that 350 miles will be just fine. Plus, add other data (like the annual mileage for most large trucks) and the 350 miles look better and better.

Weight & Hauling

Another data point that Jason was able to look at was a quote from a Pepsi executive. They said that the truck will haul loads of chips over 400 miles but that heavier loads of sodas will generally only be hauled 100-ish miles. Apparently, some people have been using the quote to talk trash about the truck, but Jason says they shouldn’t be so quick to jump to such a conclusion.

This statement, as well as several others that he shares, don’t provide important speed context. It’s possible that the larger range estimates Pepsi has given would be for lower speeds.

The weight of the battery itself is another big question people have had, and he had some insight there, too. He starts out with the weight of the Tesla Model S, which is only 100 kWh. Using similar numbers, he estimates the actual weight of an 850 kWh battery to be 10,000 lb at most. He says the weight is probably less because the container is probably not the same weight as 8.5 Model S packs.

Another question he looked at was how much cargo carrying capacity this means the Tesla Semi misses out on because it’s carrying the weight of the battery around. Trucks have only a certain legal overall weight, so carrying around up to 10,000 lb of battery means less capacity left for the paying cargo, right?

He estimates the Tesla Semi’s tractor weighs about 8,000 pounds more than a diesel-powered semi truck. But electric trucks are allowed to weigh 2,000 pounds more than diesel trucks, so the real penalty is only 6,000 pounds. Then, consider that electric motors are far lighter than a diesel drivetrain (big six-cylinder turbo plus heavy duty transmission), so there’s at least another 2,000 pounds of weight savings, reducing the capacity loss to only 4,000 pounds.

He goes further to look at the actual cargo weights that real diesel trucks carry. In truth, the Tesla Semi’s max load (which he figures to be around 44,000 lb) falls within the normal range of real loads carried in the real world. Why? Because most trucks are “cubed out” or full because the trailer is packed to the top and not full because they hit the weight limit.

The Conclusion: The Numbers Work Out, Naysayers Are Full of Bull

The argument that the Tesla Semi’s tractor is heavier, and thus it’s useless as a semi truck, just doesn’t support the weight of the numbers. It can tow almost as much as a diesel truck. It has decent range for most uses. It can have both decent range and carry nearly all of the same loads as diesel trucks actually carry today. To argue that the Semi is a scam, you’d have to argue that being able to carry 60–90% of real-world loads isn’t good enough!

He is fair, and points out that there are still problems with some of Tesla’s statements, but the actual physics of the truck do check out.

Featured image provided by Tesla.

 

 
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Written By

Jennifer Sensiba is a long time efficient vehicle enthusiast, writer, and photographer. She grew up around a transmission shop, and has been experimenting with vehicle efficiency since she was 16 and drove a Pontiac Fiero. She likes to get off the beaten path in her "Bolt EAV" and any other EVs she can get behind the wheel or handlebars of with her wife and kids. You can find her on Twitter here, Facebook here, and YouTube here.

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