The Physics and Economics of Moving 44 Tonnes at 56mph • Hacker News Board

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#91

Post by paganel » Thu, Feb 26, 2026, 11:29 PM UTC

secult wrote: post #28

For people that want to make the calculation: A truck does not need a 15 ton battery. In Europe, we have mandatory breaks for truck drivers. So you need a battery pack for max 400km of range, let's say 500km. When you have a break, you charge. For this, you need like 1500kWh battery pack, which weigths like ... wait, 15 tons. But this is not entirely correct, the real values reported are between 120-150Kwh/100km, tha…

> When you have a break, you charge.

You cannot do that, because there will never be that many charging places around. Never. The situation is so bad now that there are barely enough places for trucks to get parking spots, let alone parking spots with electric charges. I'm talking about Europe, my brother is a truck driver (right now is on a ride to Morocco, he picked something up with his truck from Hungary), I know those stories about parking spots from him.

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#92

Post by pinkmuffinere » Thu, Feb 26, 2026, 11:38 PM UTC

> Driver training that closes the 15–20% gap between the best and worst operators in a fleet.

As a naive non-trucker, I'm surprised to hear that the difference between the best and worst operator is this significant. I realize it's a bad look, and shows I thought this was a low-skill job, but I'll be honest and try to call out my own prejudice. It's cool that skill actually does have a large impact here.

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#93

Post by throwaway198846 » Thu, Feb 26, 2026, 11:53 PM UTC

HPsquared wrote: post #35

RobotToaster wrote: post #23

Earlier quoted context omitted.

From a commercial perspective, you would think the fuel savings from slipstreaming would more than make up for those five minutes.

There's a diffuse, but I suspect large, economic cost to delaying other vehicles.

You just made me imagine switching lanes microtransactions as a solution which made my soul shudder in a deep seated disgust, so I had to share it.

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#94

Post by mhandley » Thu, Feb 26, 2026, 11:53 PM UTC

It seems like trucks are a use case where battery swapping would make a lot of sense. Unlike with cars, the battery doesn't need to be a structural element, and there's much less need for it to be a strange shape, as in some cars.

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#95

Post by lazyjones » Fri, Feb 27, 2026, 1:06 AM UTC

These large trucks must go. While the mentioned numbers make some economic sense (cost per tonne transported etc.), the road wear is excessive due to the fourth power law. Most cargo can be split into smaller chunks.

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#96

Post by schiffern » Fri, Feb 27, 2026, 1:10 AM UTC

ben_w wrote: post #76

schiffern wrote: post #51

Earlier quoted context omitted.

Right. If 0.5 mph is so valuable (which I believe), how do we explain the slow trucks? How do we fix the slow trucks?

IIRC, the difference in radius between fresh tires and those worn down to just before they need replacing, changes the actual speed at any given speedometer reading by about 2%. C=πD and all that.

Makes sense.

Nowadays you could apply a long-term trim using the GPS speed, including correcting for variations due to steering inputs and elevation.

Mandatory for new trucks and grandfather old ones, like how most new vehicle standards are adopted.

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#97

Post by andrewflnr » Fri, Feb 27, 2026, 1:36 AM UTC

HPsquared wrote: post #35

RobotToaster wrote: post #23

Earlier quoted context omitted.

From a commercial perspective, you would think the fuel savings from slipstreaming would more than make up for those five minutes.

There's a diffuse, but I suspect large, economic cost to delaying other vehicles.

You mean like delaying all the people trying to go full speed in the fast lane?

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#98

Post by [deleted] » Fri, Feb 27, 2026, 1:52 AM UTC

dgacmu wrote: post #69

jjk166 wrote: post #58

Earlier quoted context omitted.

Those mandatory breaks are 45 minutes long. You're not charging 750 kWh in 45 minutes. With a fast charger 750 kWh is 2 to 7 hours. At the far more common level 2 chargers it's 18 hours. Either mandatory breaks need to be substantially longer, you need a substantially larger battery than just that required to go between breaks, or you need some sort of specialized technology for dramatically speeding up charging rate…

Tesla is, in theory, deploying a handful of 1.2MW charger sites: https://electrek.co/2026/02/24/tesla-megacharger-64-location... Assuming some amount of tesla over-hyping there, Tellus is doing 600kW chargers: https://chargedevs.com/features/inside-tellus-powers-600-kw-... So _if_ your route had those, you could charge in somewhere around 1.25h. Not enough for break time, but you can imagine starting with, say, a 1.1…

[deleted]

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#99

Post by SigmundA » Fri, Feb 27, 2026, 2:31 AM UTC

> An electric drivetrain achieves around 90%, so you only need roughly 1,600 kWh of battery capacity for equivalent range. At 0.25 kWh/kg, that’s still about 6.4 tonnes of battery — roughly 18 times heavier than the 350 kg diesel tank and fuel it replaces

This misses the fact that the motor and transmission on an electric truck is lighter than the diesel. This doesn't completely negate the issue but it does help and is not mentioned.

The 15 liter diesel engine is about 3500 lbs and the transmission with many gears is another 700 lbs.

The Tesla Semi has 3 model S motors with single speed transmissions each one is about 300 lbs with inverter so there are at least 2-3000 lbs weight savings in the drivetrain to consider.

In the US Electric semis get an extra 2000 lbs payload allowance too too so they can be 82k lbs total rather than 80.

Re: The Physics and Economics of Moving 44 Tonnes at 56mph

#100

Post by noah_buddy » Fri, Feb 27, 2026, 2:42 AM UTC

RobotToaster wrote: post #23

dmurray wrote: post #8

> At 0.5 mph differential, the overtake takes 291 seconds — over a minute of blocking the outside lane. Annoying, but it gains the driver 5.0 extra miles across a working day. The driver gets there 5 minutes earlier in exchange for causing a 7-km tailback multiple times per day? That seems like exactly the kind of thing that should be regulated away: the truck in front is limited to 90 km/h, you're limited to 90 km/h…

From a commercial perspective, you would think the fuel savings from slipstreaming would more than make up for those five minutes.

At proper breaking distance, it’s probably negligible.