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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Just imagine pushing a boulder up a hill. It requires more energy to push a rock up the hill by yourself than it does to push it up with 5 other people.
Higher gears = more people
You need more control than only the gas pedal can give. When starting up from stationary position, you need a lot of power but only little speed. Once you’re going and need to go faster, you need more speed and less power (since the car is already in motion, it takes less power).
The gears have those different priorities. First has a lot of power, but less speed. Second has a little less power, little more speed. It keeps going that way up until the highest gear, usually fifth or sixth.
You need more control than only the gas pedal can give. When starting up from stationary position, you need a lot of power but only little speed. Once you’re going and need to go faster, you need more speed and less power (since the car is already in motion, it takes less power).
The gears have those different priorities. First has a lot of power, but less speed. Second has a little less power, little more speed. It keeps going that way up until the highest gear, usually fifth or sixth.
Just imagine pushing a boulder up a hill. It requires more energy to push a rock up the hill by yourself than it does to push it up with 5 other people.
Higher gears = more people
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.
Just imagine pushing a boulder up a hill. It requires more energy to push a rock up the hill by yourself than it does to push it up with 5 other people.
Higher gears = more people
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.
You need more control than only the gas pedal can give. When starting up from stationary position, you need a lot of power but only little speed. Once you’re going and need to go faster, you need more speed and less power (since the car is already in motion, it takes less power).
The gears have those different priorities. First has a lot of power, but less speed. Second has a little less power, little more speed. It keeps going that way up until the highest gear, usually fifth or sixth.
instead of a round gear picture a lever under a load. If you push the lever to the ground the load goes up. If the fulcrum, the base the lever tips on, is close to the load, you can lift more weight. This is the same as having a small, low, gear. If the fulcrum is far from the load you can’t move as much weight but your motions are exagerated on the load side. You can move the load more with less movement on your end. This is like a large/high gear, less power but your engine needs to spin less times/slower to spin the tires more times/faster than the lower gears.
An internal combustion engine works best within a relatively narrow band of RPM. However a car needs to be able to go anywhere between 0-100MPH. The RPM of your wheels is obviously directly proportional to speed so the different gears adjust that to allow the engine to operate within its narrow RPM range.
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