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Comment by porphyra | Hacker News Reader

The cab forward design that OP prefers is so much more sensible and practical than the "standard" cab design that's so common in the US.

The Tesla Semi is more aerodynamic than its peers though. I wonder how you can improve the aerodynamics without having a narrow front or sloped windshield.

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The cab-forward design is driven by Europe having a max length for trucks that includes the tractor, whereas in the US the max length doesn't include the tractor.

For this reason I don't expect to see the Tesla Semi in Europe soon.

Which means more cabin room, which means more comfort for resting/sleeping/relaxing in addition to driving for folks that literally live in these vehicles for days or weeks at a time.

> For this reason I don't expect to see the Tesla Semi in Europe soon

I'm not expecting to see the Tesla Semi in the US soon either... it's a product in search of a problem.

Yeah he seems to not understand the importance of aerodynamics, as demonstrated by his complaint that you need extra power to run the AC because of the sloped windshield. The Tesla Semi will be consuming around 100 kW at cruising speed. Air resistance is the largest single contributor to that consumption. AC is likely to take something like 6 kW even at the highest setting. I'd bet that even in worst case heat the difference in AC consumption between vertical and sloped windshield (1 kW? less?) will be totally swamped by the improved aerodynamics. And then in the winter extra heat capture will be an advantage rather than a disadvantage.

There are some good points in here but there's clearly a strong bias.

> you need extra power to run the AC because of the sloped windshield

My impression was the the complaint about the sloped windshield was primarily about snow; the air conditioning complaint had more to do with the enormous size. It's a big glass greenhouse.

> "The angled windscreen means [...] cab overheating [...] You can solve it with A/C of course. Which will use even more power, shortening your range."

He is explicitly claiming that the angled windshield will increase power consumption and shorten range. I think it's pretty clear that the opposite is true even in the worst case.

A larger but well insulated cab could have a lower A/C energy cost than a smaller but less well insulated cab.

More air volume doesn't dramatically change the energy footprint when a stable temperature is being held for a long period of time. With sufficient insulation, the main consequence will be greater hysteresis, i.e. bringing the cab to temperature might consume more energy.

What you say is true but I interpreted his complaint as being about the increased sunlight heating up the cab, rather than changes to insulation or air volume.

It will increase power consumption if you are using the AC to melt accumulated ice or snow.

Melting 2" of accumulated snow from a 2m^2 area would take ~2 kWh which is roughly 1 mile of range or 0.2% of the battery, if my very approximate calculations are correct. Or, exactly 0 miles of range if you are plugged into a charger at the start of your journey.

But I think the original thread is right that you'll need to manually clean ice and snow off the windshield which, unlike the AC thing, definitely seems like a legitimate complaint against sloped windshields (though I have no personal experience on this point).

Snow is a non-issue, you just open the app before the ride and heat up the cabin.

You have never seen much snow if you think it can be removed by heat from inside the cab! You would need a shovel and a broom or a cab heated up at least hours before the ride. Not everywhere is cali.

Well I live in a country where it snows and have been with a Tesla in the mountains when it snowed. It takes only a little while and the snow easily falls off as soon as it's not freezed to the glass. At most you need to give it a nudge.

Have you tried waiting for the heat from a car to melt snow in a cold place on a regular car with a regular car sized windshield? On a cab like that it'll take hours.

Yes I did and it was quick. Even if it took hours, so what? You can automate it. Still saves more energy than having a non-aero cabin.

The most "aerodynamic" shape is a teardrop, with a relatively flat front end, so they could probably do something with that.

The "roll down window" thing is relatively easy to solve if they want to; you either make a seat that can slide to the side or redesign the front end.

I expect a redesign of the cab when the truck isn't selling every single one they can make.

Not to mention skirts and tails on the trailer do more to improve aerodynamics than truck modifications. Still, every bit counts I guess.

And the only time I see those tails unfurled is when it's an owner-operator driving at 55 (they know they're getting paid by the mile and so run as fuel efficient as they can).

> make a seat that can slide to the side

I wonder if that would even be sufficient. The sloped sides mean that even if the driver can sit directly next to the window, there's still a hard limit on how close he can get to whatever he is next to.

A teardrop has a "relatively flat front end" just as every rounded shape has a point where its tangent plane is vertical, even a sphere, the "less flat" shape I can think of! It doesn't mean you can place a vertical windscreen in that point and still claim you're copying a teardrop's shape.

I think the issue is, they designed a truck being worried about aerodynamics than anything else. They made it aerodynamic and forgot to ask about how it actually should work in practice.

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