The law isn't about telling you what gear you are in, it's about telling you when to shift up a gear (I'm not sure it's required to show downshifts, at least the few cars I've driven - all in the UK - only show up shift recommendations).
It's a little thing on your dashboard that pops up an up arrow and the number of the gear you should change to (and down arrow in cars that do support that).
And it's helpful because a) different cars have different engines/gear systems such that you can't learn a universal rule of "always move from gear 2 to 3 at X speed / Y RPM", and lots of people aren't good at knowing the most economical point to change into each gear even for their own car, so having the manufacturer program it in does help. I no longer pay attention to it in my car, as I've either shifted a second before it would have shown on the dashboard, or I've purposefully not gone up a gear because at that moment I care more about ability to accelerate for some reason than about being as economical as possible. But those tips were useful in helping me learn the ideal gear changes in my car without having to read up about its RPM sweet spots etc, and useful for anyone who I lend my car to who isn't familiar with the brand/model.
> "If, once in a while, you forget to shift next gear, the motor will scream at you sooner than you notice the indicator."
True if you're just thinking about not fucking up the engine, but not true if you're thinking about driving economically which is the point of the law. My car for example (a small hatchback, 1L turbo engine) gets best economy (and therefore suggests the gear changes) by upgearing when it's around about 2k RPM (not exactly, and varies by which gear), but the engine could comfortably go to 4k RPM without any screaming at all (iirc redlining is something like 6k-7k, and engine sounds fine until fairly close to that).
Upshifting at 2k RPM while accelerating is a fast way towards destroying the engine (especially the rod bearings and the dual-mass wheel) in less than 100 kkm. And I bet those upshift indicators don't take into account the temperature of the oil, do they?
Most car manufacturers don't care about longevity of their cars because they have no interest in that and EU doesn't care either. The manufacturer cares about you buying a new car every few years and EU cares about good results in some unrealistic emission tests in lab.
> "Upshifting at 2k RPM while accelerating is a fast way towards destroying the engine"
My professional driving instructor a few years ago, my car's manual and dashboard recommendations, and my two friends who work in (UK) car repair garages all disagree with you.
But I know very little about cars myself, so I can't really argue the point - but maybe there's a difference between the cars you're used to driving and my small 1L turbo engine 6 gear harchback?
My car is 9 years old with no problems yet so I can't speak to longevity of the engine beyond that, but have confirmed that following the car's guidance rather than letting the revs go higher before upshifting does give me much better petrol economy.
(And the dashboard recommendations definitely are more complex than "at X rpm recommend gear change", eg driving up steep hills the recommendations come later than when driving flat - no idea if it's taking oil temperature into control, but I also have no idea how to take that into control if I'm choosing when to gear shift...)
edit: oh, I have been told in the past that until the oil warms up from 10-15min driving that you shouldn't push the car, including not going to high revs, but nothing more specific than that general advice.
Two of my friends who had their bearings and double-mass wheel replaced in their cars around only as little as 100 - 150 kkm (one TSI another TDI) disagree with them.
The lower the RPM, the higher the momentum needed to keep the car accelerating nicely. High momentum = more vibration and faster wear. Low RPM means also worse lubrication. That's why turbo-charged and downsized "eco friendly" engines are way less durable than traditional NA engines. Not sure if they could be called "eco" at all because of this.
Assuming you aren't recommending always pushing to the red line before shifting up a gear, what makes you so confident that my car must have a higher ideal shift point than ~2000rpm, is there some rule of physics that prevents engines being made to optimise around that point?
Anecdotally I don't feel any difference in the gear shifting whether I upshift when the dashboard suggests or if I don't do it until, say, 4000rpm (though obviously do notice the different in the driving before the gear change), however if I shift up at lower revs than the dashboard suggests then I do feel a difference in the gear change itself and how easily the car seems to start in the next gear up.
Like I said, I'm not remotely qualified to speak on this subject but I'm also finding it very hard to believe you're correct (at least, correct universally for all manual cars), so I'm going to try to do some digging around for more info.
It's a little thing on your dashboard that pops up an up arrow and the number of the gear you should change to (and down arrow in cars that do support that).
And it's helpful because a) different cars have different engines/gear systems such that you can't learn a universal rule of "always move from gear 2 to 3 at X speed / Y RPM", and lots of people aren't good at knowing the most economical point to change into each gear even for their own car, so having the manufacturer program it in does help. I no longer pay attention to it in my car, as I've either shifted a second before it would have shown on the dashboard, or I've purposefully not gone up a gear because at that moment I care more about ability to accelerate for some reason than about being as economical as possible. But those tips were useful in helping me learn the ideal gear changes in my car without having to read up about its RPM sweet spots etc, and useful for anyone who I lend my car to who isn't familiar with the brand/model.
> "If, once in a while, you forget to shift next gear, the motor will scream at you sooner than you notice the indicator."
True if you're just thinking about not fucking up the engine, but not true if you're thinking about driving economically which is the point of the law. My car for example (a small hatchback, 1L turbo engine) gets best economy (and therefore suggests the gear changes) by upgearing when it's around about 2k RPM (not exactly, and varies by which gear), but the engine could comfortably go to 4k RPM without any screaming at all (iirc redlining is something like 6k-7k, and engine sounds fine until fairly close to that).