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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One more example. Have you ever used a car jack to lift up your car (or something similarly heavy?) You have to do a LOT of pumping or spinning to lift it a few inches. All that pumping movement over a long distance is gear ratioed down (via hydraulics or screw gears) to a tiny but extremely strong force able to lift thousands of pounds a few inches, where you had to move a few pounds thousands of inches.
Your engine is constantly moving but only able to apply so many hundred pounds of force, which can be converted into a tiny force across many miles, or a large force across a few feet to get up a hill for example.
You know how when you push a wheelbarrow full of heavy stuff, you have to lean into it and push hard, but slowly? And once you get going you can walk along fast, just lifting the handles lightly with your fingertips?
All right. Now imagine walking fast, with your fingers lightly on the handles, right into the back of a heavy wheelbarrow that’s standing still.
Did you stub your fingers and faceplant into the wheelbarrow? Well, that’s like trying to start a car in fifth gear (fast and light) instead of first (slow, powerful).
Equally incomprehensible is imagining yourself really bearing down and putting your back into it when the wheelbarrow is already rolling down a hill. If you can even manage that, you’d be wasting energy like crazy and wear yourself out. That would be redlining your car trying to drive 55 in first.
Gears are basically so you can vary the amount/quality
of driving force you apply in response to hills, speed changes, stop/start and the need to accelerate/decelerate. You do this naturally while walking. A car ain’t got no brain so it either needs you to do it manually, or it needs an automatic transmission which senses the load required of it and reacts by changing gears as needed.
source, drove stick for 12 years.
>Or they start talking about ratios and it just goes over my head.
So what if they start talking about ratios?
How do you expect someone to explain how a gear box works without mentioning ratios?
Why do ratios stop you from understanding the article?
To start with, gears are basically spiny levers. When you’re change sizes, you’re changing levers. Imagine you have a see saw, with the pivot in the middle. If you put a 10 pound weight on either end, it’ll be balanced and not move. Now move the pivot so it’s not in the middle. One side will be longer than the other, this is your large gear. Now if you put a 10 pound weight on the short end, you can balance it with a 5 pound weight. Of course, there’s no free lunch. If you try to move the 5 pound weight, you’ll notice that it moves a lot less than the other weight. As you shift the pivot around, the length of the levers changes and you can vary the amount of weight needed to hold that 10 pound weight steady. We already looked at a case where you need a lighter weight, but you can set it up where you need a heavier one as well( that would allow you to move it more instead of less).
So why do we need these levers in cars? Well, your engine is only capable of supplying so much torque or spinning so fast (and to make it even harder these are linked). Gears allow you to trade between speed and torque. If your car is having trouble supplying enough torque, you can trade speed for torque. If you’re having trouble spinning fast enough, you can make it spin faster by giving up torque.
One more example. Have you ever used a car jack to lift up your car (or something similarly heavy?) You have to do a LOT of pumping or spinning to lift it a few inches. All that pumping movement over a long distance is gear ratioed down (via hydraulics or screw gears) to a tiny but extremely strong force able to lift thousands of pounds a few inches, where you had to move a few pounds thousands of inches.
Your engine is constantly moving but only able to apply so many hundred pounds of force, which can be converted into a tiny force across many miles, or a large force across a few feet to get up a hill for example.
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.
>Or they start talking about ratios and it just goes over my head.
So what if they start talking about ratios?
How do you expect someone to explain how a gear box works without mentioning ratios?
Why do ratios stop you from understanding the article?
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.
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.
One more example. Have you ever used a car jack to lift up your car (or something similarly heavy?) You have to do a LOT of pumping or spinning to lift it a few inches. All that pumping movement over a long distance is gear ratioed down (via hydraulics or screw gears) to a tiny but extremely strong force able to lift thousands of pounds a few inches, where you had to move a few pounds thousands of inches.
Your engine is constantly moving but only able to apply so many hundred pounds of force, which can be converted into a tiny force across many miles, or a large force across a few feet to get up a hill for example.
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