Me monkey brain tried to do a google search on my own… me monkey brain didn’t understood a thing…me monkey brain need help
In: 1
You can imagine the car’s transmission as a set of gears. Gears mesh together with their teeth.
If the gears have the same (or similar) numbers of teeth (or the same size), the amount one turns will be the amount the other turns.
If a small gear (or gear with less teeth) meshes with a big gear (or with more teeth) and the small gear turns, it’ll take a lot of turns of the small one to make the big one turn once. This is a “slow” speed.
If a small gear (or gear with less teeth) meshes with a big gear (or with more teeth) and the big gear turns, it’ll take less turns of the big one to make the small one turn once. This is a “fast” speed.
Hope this helps!
To put it in very simple terms, the same amount of energy can be applied in two different ways– strong or fast. First gear is strong– it overcomes the car’s inertia to accelerate rapidly, but maxes out engine RPMs quickly too. Top gear is fast– it doesn’t have the same power of first gear, but doesn’t have to since it’s just overcoming mostly air resistance and internal friction to stay at cruising speed.
It’s easier to think about with a lever rather than gears and wheels IMO. When you push on the end of a lever, it moves more slowly, but with more torque(rotation strength) on the fulcrum. That’s first gear. Push on the lever closer to the fulcrum and you can move it faster, but your push won’t have the same torque. That’s like a higher gear.
Hope this cleared things up a bit.
It’s the same as riding a multi speed bicycle. Easy to take off from a stop in first gear but you start pedaling like crazy at a slow speed. Switch to a higher gear and it gets harder to pedal but you’re going faster without pedaling faster.
When attempt to explain this, many times the next comment is “I never rode a multi speed bike”.
Because car engines are TERRIBLE at low RPM, so terrible that it not only not produce nearly enough power as advertised to obtain decent acceleration, but also very likely to just stall altogether.
That’s why you need low gears to keep the engine RPM high enough at low speeds, in this way the driving force also gets amplified while the power keeps the same, meaning it has tons of force to accelerate the car, but only at low speeds.
Once the car starts moving, you shift into higher gears to use normal RPM at normal speeds.
This is why almost all conventional engines also need gearboxes, while EVs don’t. EV delivers max force all the way down to zero RPM and it doesn’t stall, making gearboxes totally unnecessary.
If the wheels go double the speed, then the engine must go double the speed. Going from 10 to 50 mph will take your engine from 2,000 to 10,000 rpm. If that doesn’t blow it up, it will run very inefficiently. So we use gears to allow the engine to run slower when the wheels are moving faster, and so save the engine.
I’m going to use made up numbers to keep the math easy.
Let’s say you have a gasoline engine whose slowest operating speed is 700 rpm (revolutions per minute – how many times the crankshaft spins each minute) and the fastest is 7000 rpm, which means the fastest speed is **10x** the slowest speed.
If you put a wheel about 28 inches in diameter on the end of that spinning shaft, the lowest speed is 5 mph, and 10x that is 50 mph top speed. But there’s a few problems with this. The nature of a gasoline engine is that it generally creates more power the faster it goes. The problem in this case is that you need more power at slower speeds so you can accelerate up to cruising speed where you need the least power. Another problem is that the engine wears out proportionally to the **square** of engine speed, so speeding it up 10x results in **100x** the wear. Not to mention that we need to go slower than 5 on occasion, and faster than 50.
This is what gears are for. Gears are effectively _multipliers_ of the engine rpm. You can multiply by numbers smaller than one to make it smaller, and higher than one to make it bigger. The auto engineer looks at the characteristics of the engine and determines the best rpm for cruising. Let’s say that our engine should do 75 mph but at only 3500 rpm (half the top speed). If the gear triples the top speed this would work. This becomes our top gear.
But now we definitely won’t have enough power to speed up to 75. So the engineer looks at the power the engine makes at each rpm and figures out what the ratio between the lowest and highest usable rpm’s are. Then you divide our final 1/3 ratio (one input rpm to three output rpm, 1/3 as a fraction) by this new calculated ratio to figure out what your second top-most gear should be. If this new gear is calculated to be a good fit for low-speed driving then you stop adding more gears. If it’s not a good low speed gear, repeat the calculations and keep adding gears until it works in a driveway or parking lot.
Because this depends on the characteristics of the engine, and technology changes all the time, the number of gears have changed over time. Most cars in the seventies had 3 gears. By the nineties it was 4 or 5 for regular cars, 6 for performance cars. Now, 7-10 gears is common in automatic transmissions.
Your transmission (the thing with gears in it) connects your engine to your wheels, but not directly. It uses gears to make the side connected to the wheels spin faster or slower than the engine.
Try picturing this in your head:
In 1st gear, your engine is connected to a small gear and your wheels are connected to a big gear. The small input gear (your engine) has to spin around lots of times (7-15ish times depending on the car) to make the big output gear (and your wheels) turn once.
In your highest gear, your engine is connected to a big gear and your wheels are connected to a small gear. So when the bigger input gear (your engine) spins once the smaller output gear (your wheels) will spin a few times. (In reality your engine will have to spin 2-3 times to make the wheels move once, there’s another gear reduction involved which is why it’s not a number lower than 1.)
If you’ve ridden a bicycle with gears before it’s the exact same concept but with the speed you pedal instead of engine rpm. That might also make it easier to understand.
Did this answer your question correctly? Your wording was a bit vague but it seemed like this is what you were asking.
Imagine you have a wheel next to you about as tall as you. It is like a giant bicycle wheel with lots of spokes. You are going to spin the wheel yourself with your own arm.
You would probably get it spinning by grabbing near the outer edge and pushing downwards right?
So that works, now try spinning it as fast as you can – you are going to eventually hit an upper limit as you keep pulling/pushing down as fast as you can near the outer edge
What if you want to go faster? Instead of applying force near the outer edge, you could go closer to the center of the wheel and spin it from there.
Hopefully if you can visualize this you can intuitively understand how the spokes near the center of the wheel are traveling slower than the outer edge of the wheel. Your arms can only go so fast but you could spin it faster by working near the center of the wheel.
You are like the engine in this case – utilizing mechanical leverage to spin a wheel faster than you could physically move your arm. That’s what gears are for.
Latest Answers