Exploring The “Hows” And “Cans” Of The Tesla Semi – Part 1

Red Tesla Semi exterior front


The Tesla Semi. Opinions are many but facts (beyond those stated at the November reveal) are few. Skepticism reigns. Among the new facts, we finally have some anecdotal test evidence stating:

  “XPO management confirmed that in their testing, the features and capabilities of the truck mostly lived up to Tesla’s claims at the launch event, including the performance vs. diesel trucks up a 5% grade (55 mph vs 45 mph), recharging time, safety/anti jackknifing features and payload (similar to a typical diesel truck, as confirmed by Tesla).”However, Jonas (Adam Jonas w/ Morgan-Stanley) noted that XPO wasn’t able to confirm the most critical figure of all: the Semi’s 500-mile range.”

Even with this test evidence partially confirming that the semi “mostly lives up” to claims, skeptics may ask HOW Tesla can:

  1. provide such powerful performance
  2. AND carry a “full” Class 8 payload AND be under the 80,000 lb tractor-trailer weight limit
  3. AND make 500-mile range
  4. AND sell it for about $180,000?

This article is the first of a four-part series to explore these “Hows” and “Cans” of the Tesla semi.

We can confirm (or re-confirm) the answers to questions 1 & 3 with EV dynamics calculations using hard data provided by Tesla and others.  At the Reveal, Elon said the semi:

Tesla Semi

Tesla Semi – Slide 1

Separately, at a quarterly conference call, Elon said the semi uses many Model 3 parts in the propulsion system, including the four driver-axle motors. We assume long-range Model 3 motors with 271 HP & 307 ft-lbs torque each (motor performance per Motor Trends instrumented test results).

Additional analytical nugget: Kman Auto showed us, in a video from the reveal, the nameplates of the drive unit reduction gearboxes, revealing that the front set of drive units are geared 23:1 (for low-speed acceleration) and the rears at 15:1 (for high-speed efficiency). When all four are operating, these drivers “blend” to create an effective 19:1 gear ratio for torque/acceleration calculations.

Tesla Semi

Screenshots from KmanAuto’s Tesla Semi video

Tesla Semi

Screenshots from KmanAuto’s Tesla Semi video

With Elon’s clues plus Kman’s gear data, it is straightforward to run a vehicle dynamics analysis in the loaded/unloaded conditions to estimate 0-60 times, climbing speeds, and total level-road range at highway speed.

Using all that data, our dynamics calculations found:

Slide 2


Performance. Confirmed. Both XPO Logistic’s tests and our calculations demonstrate the Tesla Semi CAN deliver Tesla’s claimed acceleration and climbing performance with the specified propulsion system. The skeptics should strike that item off their list. The performance simply reflects the true power of electric propulsion systems.

Payload capacity. “Qualified” confirmed. XPO said (the semi) “mostly lived up to Tesla’s claims… and payload (similar to a typical diesel truck, as confirmed by Tesla).”  “Mostly” and “similar to a typical” don’t count as firm confirmations in our book. This requires some additional analysis.

Range.Qualified” confirmed.  Our calculations jibe with other analysts’ estimates for battery size and range. But XPO did not mention anything about range in their statement. This is disturbing as EV range is THE key metric most trucking firms would test first. This leaves us speculating about the tested-prototype tractor’s installed battery pack size and tractor weight – was the prototype they tested outfitted with a full-500-mile-range battery or the smaller 300-mile battery? If the smaller battery, can Tesla actually build a 500-mile range semi-tractor weighing less than 20,000 lb. that hauls a “standard” 45,500 lb payload + 15,000 lb trailer? Is Tesla using Model 3 battery technology for the pack or will it require something new that Tesla has not yet revealed?

To help resolve these questions on tractor weight and range – In Part 2, George will deep-dive into Tesla’s Model S/Model 3 battery pack construction and known data about the semi’s pack to find clues of the Semi’s pack architecture and resulting weight and volume.

In Part 3, we build a virtual Tesla semi using George’s pack weight findings, Model 3 parts, and conventional “lightweighted” truck assemblies likely used to build the rest of the semi to estimate the Tesla semi’s actual operating weight.

Lastly, in Part 4 we look at Tesla’s likely COST to BUILD the 300-mile & 500-mile-range Semis. Can Tesla SELL them for $150,000/$180,000? And – important to Tesla stockholders –  What is the probable gross-margin?

Click here to see Part 2.

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49 Comments on "Exploring The “Hows” And “Cans” Of The Tesla Semi – Part 1"

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Great analysis. More please.


Plus, No Gears To Grind, It’s A Huge Advantage . Sounds Like a Breakthrough ! It’s like driving an automatic transmission Car without a Transmission to deal with.


The gear ratio catch was a good one by Kman. Tesla can run the semi just like their AWD Model S and X. Depending on speed and grade they can funnel power to the 2 sets of drive wheels. Up hill funnel most power to the higher Gear ratio unit.

It’s like a 2 speed without the complication of a traditional automatic transmission.

REGEN on a truck going downhill is money in the bank, Battery Bank that is. It will be like magic since electric is so powerful and efficient. Very low maintenance.

Tesla will start using these for items moving from their Nevada GigaFactory and the California Fremont factory. They walk the talk.

Unfortunately, regenerative braking is only half as-effective with loaded semis as with passenger EVs. The trailer wheels carry about 34,000 lb of load and contribute almost half of the braking force. Unless or until trailers are constructed with electric motor-generators in their axles, they will rely on their friction air-brakes.

A dynamic simulation of a fully-loaded Tesla semi w/ trailer climbing and then descending a mountain with 4,000 vertical feet of climb shows the semi would have to use about 134 kWh of extra energy to climb to the summit, but on the descent could only recover about 54 kWh through re-gen braking through the tractor’s driver-axle motors.

trailer is using friction brake only when asked to do so. The Tesla truck can use full regen before issuing the command to activate friction brake on the trailer

perhaps Tesla will offer a custom Tesla trailer with regen. Maybe there’s potentially more profit margin in a custom trailer than in the tractor.

Oh wait. Thats in part 4:)

Good point HVACman.

Trying to stop the heavy load with just the semi cab seems like a recipe for disaster.

Braking heavily without sufficient and balanced trailer wheel braking is one major cause of “jack-knifing”. The entire decelerating force induced on the trailer presses against the tractor through the king-pin connected to the tractor’s 5th wheel, which can create a lot of torque on the tractor to pivot if the tractor and trailer are not EXACTLY lined up, as would happen on a turn.

To its credit, Tesla’s semi, with individually-driven driver wheels, will have torque-vectoring wheel-speed control technology to help reduce the jack-knifing issue.

Trailer braking to control jack knifing and brake fade is not just an issue with semi’s Many, heavy recreational trailers – boat, RV, etc. towed by pickups have electric or hydraulic trailer brake systems.

Thanks for the “info dump” HVACman. I learned something today!

The whole point of Tesla’s anti-jackknife feature is to allow regen without trailer brakes.

Of course it will engage trailer brakes if it detects a high enough yaw angle. But differential regen should be enough to handle 99% of braking situations without trailer brakes.

I thought the same, and was concerned about jack knifing.
However, with 2 axles/4 wheels at the front the trailer, AND some software magic, it should be able to deal with regen and avoid jackknifing.
With that said, I would love to see trailers with small model 3 motors on the axles so as to help push, but mostly for regen.

Ah, I should have read the rest of the postings.
HVAC got to it before me.


Nice article! I look forward to the rest of the series.

“Using all that data, our dynamics calculations found:” …

You should really reveal the calculations, otherwise people will just have to take your word for it, just like they have to take Elon’s word for it ….

I could post a screenshot of the spreadsheet showing the various inputs, assumptions and intermediate results, but it would not do many a lot of good without an accompanying “tutorial” text translating the basic physics concepts and terms of vehicle dynamics from engineering-ese to layman’s terms. It would make an interesting article, though. I’ll put it on the list.

In the meantime, Here’s a fun video that covers some of the engineering basics while explaining the “how” of the Next Gen Tesla Roadster’s stated-torque and 1.9 second 0-60.


Since so far it looks like what Tesla said is true, so it seems reasonable to conclude that the range is pretty accurate too.

Adding to that, Tesla would like pretty silly if they made all this claims in front of a huge audience whilst also being recorded only to find out later they are not true.

Tesla might be often be way off with hard to predict things like release dates but when it comes to solid facts such as capabilities of their vehicles they seem to either be bang on or on the pessimistic side.

Elon KNOWS that a big % of his base are engineers who are both skeptical and good with a calculator> He speaks accordingly. Where he is specific, the numbers typically stand up – the challenge is to unearth the “secrets” behind the numbers. Makes for fun techno-sleuthing. We’ve also found that when Tesla gets vague or uses unusual phrases to describe one aspect, there are reasons for that too – to possibly obfuscate what they consider a weak area. One example: Elon was very numerically-specific about accelerations times and speeds and climbing speed at a certain % grade. But then he said the Tesla semi had 500 mile range “at highway speed”. Without saying at WHAT highway speed. Why not? Numbers mean things. Some states allow 75 mph, some 65, some like CA and Oregon only 55. And speed is a major factor for range. So “highway speed” allows Tesla to “sound” specific without being specific. I based our range calcs on 55 mph, since that is the lowest and most range-friendly Class 8 maximum legal “highway speed” in Tesla’s target market area. And 900 kWh worked at that speed. But 65 mph was only 456 miles. 75 mph was… Read more »
Engineers, just like scientists, have good reason to be skeptical. A healthy skepticism is a good attitude when examining claims. I think I share the same mind-set with them in that regard. While I remain hopeful about Tesla being able to sell its Semi Truck, my guess is that the claimed 500 mile range is somewhat optimistic, and likely won’t be reliably achieved in real-world conditions, especially in adverse conditions such as bitterly cold winter weather. Also unanswered is whether that nominal 500 mile range is with a 100% charge, or an 80% charge. A BEV passenger car can be charged to 100% of the battery pack’s usable capacity for a long trip, without worrying about that prematurely aging the pack because you’re probably not going to be doing that very often. Contrariwise, a semi truck used on a regular route can be expected to be charged to a certain level every day it operates. And if it’s expected to go 500 miles, then it’s going to be charged to that level every day. So if the truck is to have a realistic minimum range of 500 miles, then it had better have a maximum range of 625 miles, or… Read more »

beeing an engineer I really enjoy all those numbers… but in the end I am quite sure that they are not as critical as we might think.

those fleet operators who will be the early adopters will be those who want to get some publicity, some green image and those whose use cases lie as far from the maximum range as possible.

once that market is saturated… I just guesstimate that it will take some time… batteries will be better than today and so will be maximum range.

Then, probably a bit later but maybe not solar will be added to further increase range or decrease need for recharge.

Please note I did not use any numbers.
222 😉 This is the dawning of a new age… Let the sun shine!

I think that you are overrating the early adopters for marketing.
1-3 trucks would be marketing.
3-10 would be trials.
But more than 10 is almost certainly called that we have seen enough and need to switch over for economical reasons.

Good points it would have better for them to state the speed and also the outside ambient temperature.

It’s unfortunate that the quoted ranges are often the average for a variety of conditions and not for the worst case scenario. That’s one thing that is a shame about quoted EV ranges.

For cars I tend to go by kWh * 3. Even that will probably be a bit too optimistic for the worst possible conditions but good for a vast majority of cases.

“2. AND carry a “full” Class 8 payload AND be under the 80,000 lb tractor-trailer weight limit” There are exceptions to the 80,000 lb tractor-trailer weight limit that are codified in federal law and regulations that allow certain alternate-fuel tractor tailers to significantly exceed the weight limit on federal interstate highways, and on state highways in states that have passed laws to follow the federal exceptions. For example, on federal interstate highways the the weight limit for CNG tractor trailers is 82,000 lbs, and 24 states follow the federal weight limit for CNG tractor trailers. The 2,000 lb higher weight limit for CNG tractor trailers was enacted to because a CNG powertrain and fuel tanks are heavier than a diesel powertrain and fuel tanks, and the federal government didn’t want to penalize the cleaner emmisions albeit heavier CNG tractor with a reduced maximum trailer payload. Apparently, the 2,000 lb higher weight limit offsets a 2,000 lb heavier CNG power train. Since a EV long range Class-8 tractor with its ginormous battery pack will weigh significantly more than a diesel Class-8 tractor trailer, the question becomes: will EV tractor-trailers get a Federal exception to the 80,000 lb weight limit, and by… Read more »

Good point. So far, no state has an “allowance” for electrified tractors. Some states do allow a 400 lb “allowance” for the aerodynamic devices installed on trailers. But not all.

I think the importance of tractor weight is overstated. According to one claim I’ve read, 90% or more of tractor-trailer loads don’t push the weight limit. Space inside the trailer is more likely to be the limitation, rather than weight.

Of course, that’s not to say that trucking fleet operators don’t worry about weight limits. Anybody who knows what a highway weighing station is for, and sees all the trailers stranded there because the truck was over the weight limit, knows it is an important consideration.

But let’s keep in mind that the majority of tractor-trailer routes are shorter ones, which could be serviced by the shorter-range Tesla Semi Truck; a truck with a smaller, lighter battery pack; one which won’t intrude as much into the maximum weight of cargo. Even if all Tesla Semi Truck use were to be restricted to the shorter range trucks, that’s still a huge potential market for Tesla.

Tesla doesn’t have to serve 100% of the potential heavy freight truck market from the very start. It just needs to get a firm toe in the door; the rest will inevitably follow as battery tech continues to improve.


Cool. Thats partly what I wanted to say!

The relevance of absolute numbers is generally overstated!

Progress is what matters.

And we are definitely seeing progress. That’s great! Tesla is great! Thanks Nikolai! (I hope you hear me 😉

Sorry guys for not being too serious today!
Smile and hang loose!

you skimmed by something important here.

If operators are saving 25 cpm on fuel costs there are some logistical adjustments that will be worthwhile making in order to capture those cost advantages.

So, there will be opportunities to re-optimize around a different fleet mix.

The important thing is that innovation adoption is not an all or nothing thing.

I thought that the EV semi was supposed to be LIGHTER than the diesel?
That is what Tesla stated earlier.
I recall expecting it to be heavier and was surprised that was not the case.

Most of the trucks failing weight stations are about distributions of weight, not total.

Its interesting the difference in approach between tesla and MB, Nissan and others to the commercial market

Can you guys also address how they can sell electricity at 7 cents per kWh when the industrial average is above that when factoring in demand charges. Are they expecting to sell power at a loss??? You can’t just list the average industrial rates and say they are charging the break even. Those chargers cost $, the demand charges cost $, etc.. if these truly will become the backbone of the trucking industry I think it’s important to understand the actual cost of things.

I don’t know, but perhaps he plans to create his own utility-sized solar PV system ( using Solar City-built panels from Gigafactory 2) in the southwest and sell power to the grid at $0.05/kWh, then work out deals with the various utilities to buy it back at $0.07. But then there are the demand charges to cover the utility infrastructure costs. So he’d have to add massive battery banks, too (at $$$$$ expense) and then the stations themselves. Picture a station for 5-10 semi’s, each charging at 1.4 mW. That would require 100KV lines to it, a large substation, etc. etc. The installed costs would be huge. The business model does not look good. IMHO, the “mega-charger” is currently a pipe-dream – technically do-able but way down on the priority list. The Tesla Semi is a day-cab unit. No sleeper. No room for a second driver. Not meant for long multi-day on-the-road trips. Out and back in a day. Perfect for 500-mile range. And the truckers looking at the Semi see that and know it. All those who have put down reservation deposits and considering ordering one or more of the 1st Gen Semis likely will install “kilo” chargers –… Read more »
I don’t buy that an electric utility will have to install a substation to service every individual Megacharger. Since Tesla’s advertised price for electricity is slightly above the national average for industrial electricity rates, it seems pretty clear that Tesla plans to only install Megachargers in industrial areas, where high power demands are expected and already provided for by the utility. I also don’t buy the argument that Tesla would have to install massive banks of batteries at any solar farm intended to sell electricity to utilities. Tesla doesn’t have to do that on a nationwide basis; it can pick and choose the places where they’ll maximize their ability to sell electricity to the utilities at their minimum cost for installation. That rather strongly suggests they’ll only install solar farms in areas where the utility is happy to buy solar electricity without the solar farm needing anything more than a relatively small bank of batteries to smooth out power fluctuations lasting no more than a few seconds. I think it would be very wasteful to require every individual supplier of renewable electricity to smooth out their own power output over a day or even an hour. The utility should be… Read more »

There is actually a good economic case for installing batteries directly at solar farms. For one, it saves on transmission costs. Moreover, it improves costs and efficiency, since DC power from the solar cells can go to the battery directly; while inverters are used only at the grid connection point.

you might want to check out the latest RE (utility scale) power tender in CO in Dec 2017: wind+storage 2.1 c/kwh; PV+S 3.6 c/kwh. PV+S costs have been falling at >15%/yr.

Sited at customer sites, Tesla won’t be installing at such scale, but its not hard to imagine why they are using 7 c/kwh as their baseline if you go forward to 2020 onwards.

I don’t understand what the fuss is about. National average price for industrial electric power is only 6.95¢/kWh, so Tesla’s 7¢/kWh is below that figure. I also don’t believe that demand charges will be anywhere near as important as Tesla bashers keep claiming. (Not suggesting HVACman is a Tesla basher, because he’s not. But in this case he certainly seems to be repeating one of their claims.) Let’s look at how demand charges are figured, or at least how one electric utility figures them: Explanation of Demand Charges Depending on how they use electricity, electric utility customers are charged for different electric services. Along with a basic customer charge — which is a set fee paid monthly or seasonally — most customers pay for the energy they use (measured in kilowatt-hours, abbreviated kWh). Larger users of electricity are also charged for something called demand (measured in kilowatts, abbreviated kW). The electric utility uses demand meters that… register the highest rate of electrical flow (or current) during a billing period. It’s actually a little more complicated than that, because the meter records an average flow for every 15 minute interval. The customer is billed for the highest average 15 minute flow… Read more »
Demand charges vary by location. In California, it can be VERY high, as interior California in the summer gets HUGE air conditioning loads that spike around 4-5 pm, then collapse to nothing by midnight. I know for a fact. Some of my clients use various demand-reduction techniques such as thermal ice storage to control their demand charges. If California becomes a major location for Tesla Semi’s, charging demand charges will be a big factor. FYI, demand charges can be as high as $20/kW per month (It is in Redding). So a peak 10 MW demand could be 10,000×20 = $200,000/month. To get a handle on how big 10 MW is, the city of Redding, CA is 90,000 people and a regional hub with lots of retail and moderate industrial. They have their own utility. Their average TOTAL demand (less air conditioning) is about 70-80 MW. re: substation vs “just large electric service” At the 10 MW service range, with an intermediate-distribution voltage of 12kV, the peak amps would be 500 amps – on TOP of any existing load on that distribution line. It really depends on how loaded the existing 12KV distribution lines are to determine if that new load… Read more »

In fact, multiple studies have been done on these issues and showed that overall the grid (save in the northwest) handles everything fine.
The problem is that if daytime charging jumps up to more than 15% of total vehicles, that it would cause major issues with the production.
OTOH, if less than 10% of total vehicles use daytime charging, then not only can the grid and power handle it, but that it would actually LOWER the costs by shifting more production from peaking plants to baseload.

This is why I am opposed to anything with less than 150 MPC, esp plug-in hybrids. Far too many ppl are plugging in during the daytime.

Or a rather small data center.

Personally got a tour of a 10mw miracle of a data center. It used brains to cool it as much as the brawn of chillers.

You’ve established that a work day is 4.6 % of a month. What this has to do with the price of tea in China is beyond me.

Pushi – HVAC man has a handle on this better than you do – he at least has seen a demand charge before.

As long as the stock market keeps rising I don’t see any problem for Tesla Megacharger loads – at least they get a few cents for their trouble from the trucking firms.

The existing supercharger network must be a much bigger expense for Tesla since for the majority of users Tesla doesn’t get anything.

Its difficult for me to form an opinion on much since so little public information has been given. It would be interesting to know what the trucking firms who are dipping their toes in the water to experiment with the trucks what promises or commitments they have been given.


“National average price for industrial electric power is only 6.95¢/kWh, so Tesla’s 7¢/kWh is below that figure”

below or above… who cares 😉
it’s roughly OK.

and I agree demand charges are overrated 😉 and if Tesla really would really struggle to reach the 7¢/kWh they could sell for 7.1 or 7.2 so what’s all that discussion about?

and if national average is x then why not just build megachargers where price (incl. demand charges) is below x.

and if all that doesn’t work out just develop some V2G functionality and reduce net cost by providing grid stabilizing and storage service…

and at what times will those chargers be used? night? day?

Well in the end I am just quite sure that those at Tesla who calculated that 7 are people who can calculate and have sufficient information to be closer to reality than we are and still have a margin (while that margin might be small… who cares? (Stock market people… OK…))

(and dammit I used numbers in this post…;-))

Nonetheless take it easy folks and keep calculating! I keep on enjoying the numbers and the progress! Yieeeeehaa!!!

Demand charges are only over-rated if you’re not the one paying for them.

In Tesla’s case, I don’t think it really matters.

However for several businesses its more than 1/2 of the total electric bill – something Pushi would never understand.

Uh no.
industry average for production is .03/kwh.
business average is .07/kwh.
retail to homes is .12/kwh.


Last but not least:

Thank you HVACman for providing all those numbers and for taking the time to do the math!
And for all those first hand information about demand charges etc… I enjoyed reading this.

Keep up your good work!
…and keep your head up high 😉 just singing…

HB from outer space:

“…if national average is x then why not just build megachargers where price (incl. demand charges) is below x…”

The fallacy there is assuming the charges are the same every month or the percentages of them are always the same.

It depends on what happens with the usage during the month. Of course, there are places where a Truck Stop might want to be placed in an area with large utility costs. Of course, if Tesla is only charging 7 cents/kwh regardless(whether to the truck or to the charger has as of yet been up in the air), then it won’t matter to the firm what the utility actually charges since the trucking firm’s rate will be fixed.

Perhaps if you spent more time on the earth you’d see how things work in practice.

Look at in terms of percentage market. It’s true, some trucks see > 500 miles a day.But just how many not really all that high a percentage.

Most are used sub 300 miles / day.

It is claimed just short of 300,000 of class 8 a year are sold.

Even 1% market share is 3,000 trucks sold, and a damn good business in itself. How long do you think it would take for them to ramp to 3,000 a year something like 15 a day presumming 200 day work year?

1% is more than enough by itself to significantly reduce air pollution. More importantly it goes a long ways to pushing the experience curve on battery production for further cost reduction performance gain.

It’s at the point of the curve that each and every use case for any batteries drives us to the point where electric everything. Well nearly everything, more like functionally everything.

Remember each supports the gains of the other. A few GW of batteries grid storage, a few GW passenger cars, a few GW of Semi’s each drive us down the Swanson’s curve, experience curve for people allergic to renewables.

Obviously replace “a few” with many, drives it even harder.