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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Here’s a different way to think of it: Your engine and wheels need different things. Gears let them both be happy.
Your tires are about two feet wide, so they’re about six feet around, and they turn once every six feet you drive. That means they turn about 900 times per mile, no matter how fast or slow you go. At 450 rotations per minute of the wheel, you’re going 30 mph. At 900 rotations per minute, you’re going 60 mph, a mile a minute. At 1800 rpm, you’d be going 120 mph.
Your engine, on the other hand, idles at about 600 rpm, and is healthiest around 2500-3000 rpm at highway speeds. It can’t really go slower than 600 rpm. Without gears, your minimum speed would be 600 wheel turns per minute, which about 45 miles per hour!
So, at low speeds, you may need to be able to spin your engine 5-10 times for each wheel turn. At higher speeds, that number shrinks, because the engine turn number and the wheel turn number are closer to each other.
Riding a bicycle up a hill would be the simplest most intuitive example. You have a fixed amount of force you can apply to the pedal. You need a higher gear ratio to gain leverage to have enough force to overcome the incline. The opposite is true when riding down the hill.
Look at a 10 speed bicycle. Gear ranges are ratios between the crank and wheel. Three turn of the crank is 1 turn on gear 1, 2 turns on gear 2, 1 turn on gear 3, etc. The engine cannot go below a minimum rpm without stalling or above a maximum rpm without damage. The gears allow the engine to be in it’s “happy place” and do meaningful work for the driver at all speeds.
Your engine has a narrow range of RPMs where it works. Too slow and it stalls out because friction slows it down before the next piston can fire, and too fast and it tears itself apart.
If you need to be able to go at a crawl in a drive thru or pulling into a parking spot (maybe 5km/h), and you set that for your lowest RPM (about 1000 RPM), you would top out at 5000 RPM being 25km/h. That’s not very useful.
So you need to add gearing in. Each gear in the car is a different ratio of engine turns to tire turns, letting you cover the entire range of speeds that your car needs to go.
As an added benefit, combustion engines are most efficient at lower RPMs, so you can also typically get to your cruising speed in an appropriate gear to minimize your RPM, which decreases fuel consumption.
You might notice that electric cars don’t have gears. Because their engines don’t have the same moving parts with pistons firing (only the actual driveshaft rotation), they don’t need gears because they can just directly drive the tires at different RPMs.
Riding a bicycle up a hill would be the simplest most intuitive example. You have a fixed amount of force you can apply to the pedal. You need a higher gear ratio to gain leverage to have enough force to overcome the incline. The opposite is true when riding down the hill.
Your engine has a narrow range of RPMs where it works. Too slow and it stalls out because friction slows it down before the next piston can fire, and too fast and it tears itself apart.
If you need to be able to go at a crawl in a drive thru or pulling into a parking spot (maybe 5km/h), and you set that for your lowest RPM (about 1000 RPM), you would top out at 5000 RPM being 25km/h. That’s not very useful.
So you need to add gearing in. Each gear in the car is a different ratio of engine turns to tire turns, letting you cover the entire range of speeds that your car needs to go.
As an added benefit, combustion engines are most efficient at lower RPMs, so you can also typically get to your cruising speed in an appropriate gear to minimize your RPM, which decreases fuel consumption.
You might notice that electric cars don’t have gears. Because their engines don’t have the same moving parts with pistons firing (only the actual driveshaft rotation), they don’t need gears because they can just directly drive the tires at different RPMs.
Look at a 10 speed bicycle. Gear ranges are ratios between the crank and wheel. Three turn of the crank is 1 turn on gear 1, 2 turns on gear 2, 1 turn on gear 3, etc. The engine cannot go below a minimum rpm without stalling or above a maximum rpm without damage. The gears allow the engine to be in it’s “happy place” and do meaningful work for the driver at all speeds.
Your engine has a narrow range of RPMs where it works. Too slow and it stalls out because friction slows it down before the next piston can fire, and too fast and it tears itself apart.
If you need to be able to go at a crawl in a drive thru or pulling into a parking spot (maybe 5km/h), and you set that for your lowest RPM (about 1000 RPM), you would top out at 5000 RPM being 25km/h. That’s not very useful.
So you need to add gearing in. Each gear in the car is a different ratio of engine turns to tire turns, letting you cover the entire range of speeds that your car needs to go.
As an added benefit, combustion engines are most efficient at lower RPMs, so you can also typically get to your cruising speed in an appropriate gear to minimize your RPM, which decreases fuel consumption.
You might notice that electric cars don’t have gears. Because their engines don’t have the same moving parts with pistons firing (only the actual driveshaft rotation), they don’t need gears because they can just directly drive the tires at different RPMs.
The engine is only likes to rotate at certain speeds. So to keep the engine at its happy speed while the car is moving at different speeds you need to change gears
The engine is only likes to rotate at certain speeds. So to keep the engine at its happy speed while the car is moving at different speeds you need to change gears
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