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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As an extended example: the gear that is connected to the engine has 20 teeth. You have two gears connecting to the wheels: one with 10 teeth and one with 40 teeth. The teeth of the gears interlock with each other and move together, tooth-by-tooth. Each rotation of the wheel-gears means one rotation of the wheels.
If you’re on the 40-tooth gear, your engine needs to spin twice for the wheel to spin once (engine gear has 20 teeth, you need to spin the wheel gear by 40 teeth, so that’s two spins of the engine gear). That means you’re either traveling slowly (wheels spinning slowly) or you’re traveling quickly and revving the engine very fast.
If you switched to the 10-tooth gear, the reverse is true; each time your 20-tooth engine gear spins once, your wheel gear has spun twice (20 = 10 x 2). So you can travel much more quickly than you could on the 40-tooth gear (4 times as fast, for the same engine speed).
The point of this is that combustion engines are most efficient at a narrow range of speed, so you choose different gears to suit the speed that you want to travel at. Cruising through the neighborhood at a kid friendly speed is probably 2nd or 3rd gear, with lots of teeth on the wheel gears; cruising down the highway with the music blasting and no traffic is probably a higher gear like 5th or 6th, with fewer teeth on the wheel-gears.
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