Live data from Hacker News

The Physics and Economics of Moving 44 Tonnes at 56mph

mikeayles.com

11–20 of 123 posts

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

#11
> This isn’t advisory. It’s a physical limiter in the engine’s ECU. The truck cannot go faster.

I live in Latvia (in the EU) and see a significant part of our ARTICs on the roads go well past 90km/h daily. I presume their fleets do monitor the speed and alert the driver if speeding for a prolonged period of time but they are obviously not physically limited. Maybe the limits do come from the factory but get disabled? I really couldn't say.

A recent journalistic investigation uncovered a problem with the weight limit not being followed on a mass scale too. Specifically by our lumber industry whos drivers are incentivized to break the law. Even if you see a dangerous overloaded truck on the road and call the Police, it is likely no action will be taken because there only a couple of units in the country that are equipped to weigh a freight truck out in the field.

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

#13

I was reading the NASA truck aerodynamics thread earlier and realised that commercial freight is one of those fields that touches everyone's daily life (everything you own arrived on a truck) but sits in a complete knowledge blindspot for most people. I work in fleet fuel efficiency and wrote up the foundational mental model, covering why trucks weigh what they weigh, why they're all doing exactly 56mph, why diesel i…

A very well written article! I'd add a few things though.

> Every kilogram you add to the vehicle is a kilogram you can’t carry as freight.

That is only relevant when hauling bulk loads, think ore, soil and the likes, or you're carrying a trailer full of IBC liquid containers. I worked in stage lighting stuff, our trailers were at least 3/4 foam by volume, they didn't even come close to maxing out their weight.

> A battery pack storing equivalent energy would weigh on the order of 16 tonnes at current lithium-ion energy densities.

You don't need to haul a fully equivalent battery. Drivers have to have their mandatory rest breaks of 30+15 minutes here in Germany - that's enough to charge 300-400km of range. Additionally, they can be charged at loading docks, provided the freight base or the customer have chargers set up.

> For a driver paid by the mile, or on a delivery schedule measured in minutes, that overtake is rational.

Payment by mileage is illegal in Germany, as a trucker you need to be paid by the hour and you need to be paid under German minimum wage law as long as you're physically on German roads. Trucker companies from Eastern Europe are infamous for evading that, but as our customs enforcement (who also do the road inspections for rest breaks and minimum wage) ramps up, it's getting better.

The remaining problem are the dispatchers, quite a few of them hand out routes to their drivers that are barely achievable when operating legally (i.e. trucks with working speed governors, drivers taking their rest breaks). Competition is fierce, there used to be talks about passing laws to force dispatchers to not give barely-legal orders but I'm not sure where these went following our government's collapse last year.

> An electric drivetrain achieves around 90%, so you only need roughly 1,600 kWh of battery capacity for equivalent range.

Yup, and most importantly, you mentioned regenerative braking cutting down on brake wear - but it's not just cutting down there, the truck can actually save a fair amount of energy as well, at least outside of highways where the truck is mostly just coasting along.

Trucks, given the right infrastructure, are also viable for running them electrically in the mid-range nowadays as a result.

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

#16
post #6

Is this correct — HGVs can go faster on dual carriageways than motorways? "UK speed limits for heavy vehicles are also more complex than most car drivers realise. Articulated trucks over 7.5 tonnes: 60 mph on dual carriageways, 50 mph on single carriageways, 56 mph (limiter) on motorways" Not able to find a source that verifies that

[deleted]

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

#17
post #4

Why is fuel consumption 5x more per mile but 10x more per hour, if the trucks are moving more slowly than cars?

Yeah the numbers in this article are all over the place. "291 seconds" also got rounded off to "over a minute", when it's closer to 5 minutes

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

#18
post #7

I was reading the NASA truck aerodynamics thread earlier and realised that commercial freight is one of those fields that touches everyone's daily life (everything you own arrived on a truck) but sits in a complete knowledge blindspot for most people. I work in fleet fuel efficiency and wrote up the foundational mental model, covering why trucks weigh what they weigh, why they're all doing exactly 56mph, why diesel i…

this is well written. thank you - you broke down the economics nicely. I do think maybe with a hub & spoke model - big trucks move loads to hubs -- then smaller electrified trucks cover the less than 200 miles from hub to spoke. electrified smaller trucks and vans are already economical today. you get to benefit from using diesel for long haul routes - while also - better economics on the electrified front i.e a hybr…

Trains for longer distances and then electric trucks for last mile

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

#19
post #14

.

They mention this later in the article. It's still about 6 tonnes for the battery to store as much effective energy as the diesel tank.

It seemed like the author had moved on from EVs so I thought he was done, but okay. Should've finished I guess.

The article still never accounts for the fact that motors+inverters are ~2 tonnes lighter than an engine+transmission.

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

#20
post #14

Earlier quoted context omitted.

They mention this later in the article. It's still about 6 tonnes for the battery to store as much effective energy as the diesel tank.

It seemed like the author had moved on from EVs so I thought he was done, but okay. Should've finished I guess. The article still never accounts for the fact that motors+inverters are ~2 tonnes lighter than an engine+transmission.

Or your reading comprehension is not good enough. I didn't have any problem finding the paragraph where he author goes into extra detail. Who can say.
Post reply on HN