Tesla’s Electric Semi is a Mega Truck

Tesla just unveiled the Semi, the company's fully-electric tractor-trailer. Let's look at the numbers.

Tesla calls its new electric truck the “Semi,” and while the name may be short on creativity, the design makes up for it. This is a mega truck on many levels, so let’s take a look at the features and the numbers.

Tesla Semi Features

Starting with the driver’s experience, the Semi sports a sleek, user-friendly cockpit with a 360-degree view provided by a combination of windows, surround-view cameras, and touchscreens. (Tesla CEO Elon Musk claims that the windshield can withstand a thermonuclear explosion; let’s hope nobody decides to test that in the field.) Although the truck isn’t autonomous, it does include some of the underlying “autopilot” technology, such as lane-departure warnings, automatic emergency braking, and jackknife prevention. Also, notice the absence of a stick shift. The Semi has one gear – no shifting required.

The Semi’s 500-mile range is more than sufficient for the majority of trucking applications, and its battery pack can be quick-charged to 80% capacity in 30 minutes. (More on that below.) Its powertrain will accelerate the fully-loaded Semi from 0 to 60 MPH in 20 seconds (five seconds if unloaded), and the truck can climb a 5% grade at a steady 65 MPH.

Tesla claims that the Semi uses less than 2 kWh of energy per mile traveled, which, over the life of the truck, will save more than $200,000 in fuel costs. Musk says that the fuel savings and reduced maintenance costs will offset the higher initial price, giving a two-year payback period and the lowest total cost of ownership in its class.

Like most of its new products, the Semi’s specifications are shrouded in mystery, so I took a few educated guesses and ran some numbers. I can’t verify the company’s claims on performance, but I can at least show that they’re realistic, given the current state of the technology.


If I told you that my vehicle could accelerate from 0 to 60 MPH in 20 seconds, you’d most likely respond with an unimpressed yawn. But if I followed that up with, “My vehicle is a fully-loaded Tesla Semi with a net weight of 80,000 pounds,” you might be a little more impressed. And if you were behind that mega truck on an interstate highway on-ramp, you’d be grateful.

Four independent motors deliver a torrent of power to the wheels, giving the Tesla Semi its rapid acceleration. Tesla won’t divulge the details of its motors, so I whipped out an old envelope and did some calculations on the back. First, a little research revealed that a typical truck of this class can accelerate at 2.2 ft/s2 if its weight-to-power ratio is 100 lbs/hp. At that rate, a truck would reach 44 ft/s (30 MPH) after 20 seconds. Since the Tesla hits 60 MPH in the same amount of time, its acceleration must be twice as high, roughly translating into a weight-to-power ratio of just 50 lbs/hp. That means that an 80,000 lb truck would have 1600 horses under the hood – or, more accurately in this case, 400 hp (nearly 300 kW) per motor. That’s a total of 1.2 megawatts of motor power.

Enzo Ferrari famously stated, “Aerodynamics are for people who can’t build engines.”  A typical semi has drag coefficient around 0.6; Tesla engineers scoffed at Ferrari’s false dichotomy and complemented the Semi’s robust powertrain with a sleek aerodynamic drag coefficient of 0.36. (Ironically, the Tesla Semi’s drag coefficient is nearly as good as that of a 2016 Ferrari 488 GTB.)

Mega Batteries

The company is keeping mum on the battery capacity also, but given its own estimates of range (500 miles) and fuel economy (2 kWh/mi), I can skip the envelope and do the math in my head: this truck’s battery must hold about 1000 kWh, or one MegaWatt-hour.

Based on the battery capacity and range, the sustained motor power (at typical cruising speed) would be 120 kW, or 30 kW per motor. Thanks to the Semi’s low drag and Newton’s First Law, once it gets up to speed, the truck only needs about 160 hp to maintain a steady highway velocity. Regenerative braking takes advantage of inertia, turning the motors into generators to recharge the batteries, and reducing wear on the brakes. Tesla says that the factory-installed brakes are designed to last the life of the truck.

Mega Charger

Tesla claims that the Semi’s batteries can be charged to 80% capacity (400-mile range) in 30 minutes, using one of its appropriately-named “Mega Chargers.” To give a battery 800 kWh in half-an-hour, the charger will need to pump out a whopping 1.6 MegaWatts of power. (If you thought my previous “Design the Filling Station” challenge was difficult, good luck designing a Mega Charger station.) Oh, and to make it a mega-challenge, Musk says that the Mega Chargers will be solar powered.

Mega Warranty

To top off all the “megas,” Tesla stands behind the Semi with a million mile warranty.

Despite the yet-to-be-revealed price tag, major players in shipping, like Wal-Mart and J.B. Hunt, have already pre-ordered several Semis for their fleets. Will the Semi deliver?

Watch the announcement here.

Images and video courtesy of Tesla Motors


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