I get that low gears > more power but low speed. I get that high gears >low power but high speed.
But can someone give me the brain dead intuition of why you need to change gear “sizes”? A single sentence if possible.
I’ve tried Googling it but they always use a bike example. I’ve never ridden a bike. Or they start talking about ratios and it just goes over my head.
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Maybe the best way to think about it is by thinking of levers — as you’re probably aware different gear sizes give you different amounts of leverage. The other consideration here is engine life and damage — running the engine at too high and rpm will shorten its lifetime and possibly permanently damage it.
A low gear is like a really long lever — gives you a lot of leverage and force; but because it’s long, you have to move it across a longer arc. This analogy equates to the engine spinning at a higher speed with more power.
A high gear is like a really short lever — easier to move because it’s shorter, but it provides less leverage because of it. So the engine isn’t turning as quickly, which is good, but it’s also providing less power to the wheels.
The other piece of this to consider is that the engine and the wheels are mechanically linked, which is why the wheel speed and the engine speed are important considerations — it’s great to have the wheels spinning really fast, but that necessitates the engine spinning really fast as well, which usually isn’t ideal.
The reason you can’t just use the high gears all the time is because of the “leverage:” the high gears just can’t move the car from a standstill. However, they’re really good at *keeping the car moving,* because once you’ve got the car rolling, you need less energy to keep it rolling. Using a high gear to deliver all that energy can be done of course, but as you probably know, using a low gear at high speeds makes the engine spin really hard. So the trade off is using a higher gear at higher speeds, which allows the engine to still provide some power (because you need less at speeds than you do when starting) but also allow the engine to spin slower.
(There is of course a lot more to this — as you go faster, air resistance begins to become a real problem and even high gears will struggle to provide power to overcome that resistance while also keeping engine rpm low, but that’s for really extreme examples)
The point of having the gears is to select which “lever” is ideally suited to the task at hand — you want something that will deliver enough power for what you want, but won’t unnecessarily wear the engine.
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