Why do manual cars/motorcycles stall if you don’t give them gas as you let go of the clutch?
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engines are built around using the inertia of the cylinders and crankshaft spinning to move them form power stroke to power stroke, and siphoning off the rest of the energy to do work. If you put too much load at once on the engine, you draw too much energy “out” of the system and then cylinders fail to properly compress the fuel to power the next cycle, dont ignite properly, and then theirs no more power for the next cycle.
modern engines use an electric starter to get them going, which is basically a small electric motor to spin the crankshaft and cylinders. other engines might use the ripcord for the same purpose, or even the old school hand crank.
Engines generate more power the faster they’re running (generally speaking).
In order to get the car rolling, you need enough power (torque) to overcome the cars inertia.
If you don’t give enough power the engine can’t complete its cycles and so it just stops running.
You can fix this by applying more gas and increasing the power output of your engine, or by lifting the clutch slower so that it slowly starts slipping and gradually bringing the car up to speed instead of dumping the entire weight of the car on the engine at once.
Let’s try a simpler explanation:
Imagine a small ferris wheel that’s powered by a person. This ferris wheel only has one handle attached to it that the person can use to push it. The person powering the wheel always needs to give the wheel enough of a push so it manages to complete a full rotation, so he can reach the handle again the next time.
If he doesn’t give it a strong enough push, the wheel would come to a stop while the handle is still somewhere in the air where he wouldn’t be able to reach it, so it’s effectively stalled. If there’s something slowing down the wheel, the risk of stalling increases.
Engines are quite similar. They can only give the spinning crankshaft a ‘push’ at certain points of the rotation, and releasing the clutch slows down the crankshaft because some energy is transferred to the wheels.
Let’s try a simpler explanation:
Imagine a small ferris wheel that’s powered by a person. This ferris wheel only has one handle attached to it that the person can use to push it. The person powering the wheel always needs to give the wheel enough of a push so it manages to complete a full rotation, so he can reach the handle again the next time.
If he doesn’t give it a strong enough push, the wheel would come to a stop while the handle is still somewhere in the air where he wouldn’t be able to reach it, so it’s effectively stalled. If there’s something slowing down the wheel, the risk of stalling increases.
Engines are quite similar. They can only give the spinning crankshaft a ‘push’ at certain points of the rotation, and releasing the clutch slows down the crankshaft because some energy is transferred to the wheels.
Let’s try a simpler explanation:
Imagine a small ferris wheel that’s powered by a person. This ferris wheel only has one handle attached to it that the person can use to push it. The person powering the wheel always needs to give the wheel enough of a push so it manages to complete a full rotation, so he can reach the handle again the next time.
If he doesn’t give it a strong enough push, the wheel would come to a stop while the handle is still somewhere in the air where he wouldn’t be able to reach it, so it’s effectively stalled. If there’s something slowing down the wheel, the risk of stalling increases.
Engines are quite similar. They can only give the spinning crankshaft a ‘push’ at certain points of the rotation, and releasing the clutch slows down the crankshaft because some energy is transferred to the wheels.
You don’t necessarily have to give it gas, but it does make it easier to get going.
Stalling happens when the engine slows down to a speed (RPM) that isn’t fast enough to get the piston to the next power stroke (when fuel is burned to generate power). The piston already has to work against exhaust and air-fuel pressure, releasing the clutch adds the load of moving the car to this
The clutch is a pair of plates that can be separated by pressing the pedal and releasing it lets them touch again. Releasing further increases the pressure between the plates, which increases friction, making them stick together more. This forces the speed of the engine and the input of the gearbox to match
Each gear in a gearbox has a movement speed associated to an engine speed (RPM) and when you change gear, you change the ratio between those 2 speeds. The input speed comes from the engine, it’s converted to the output speed, which determines how fast the car goes.
With these 3 bits of information, we can put it together:
When the clutch is completely released, the engine and gearbox input speeds are forced to be the same. This results in an output speed that moves the car. If we have a stationary car, which would do 10km/h at idle in first gear, then the moment you drop the clutch, it should instantly be moving at that 10km/h speed. What happens instead is that the resistance coming from the car stops the engine. You can stall in a moving car too, if the engine is forced to turn slower than it needs to reach the next power stroke.
The way slowly releasing the clutch helps is by decreasing the pressure between the clutch plates. This allows them to have a speed difference, essentially converting some of the engine’s power to heat instead of movement. This also means that part of the force that would stop the engine is converted to heat, letting the engine keep turning easier. While the clutch is allowed to slip, the car is less efficient and wears the clutch out, but with normal operation, this wear takes decades to become noticeable. Pressing the gas while getting moving gives more power to the engine, letting you put more load on it but heating the clutch up more in the process (which is fine if you don’t go crazy with the gas). If your engine is more powerful than the grip of your tires, then at high enough RPM, it will be able to handle the clutch being dropped instantly, but in that case the wheels will spin (which also converts mechanical resistance to heat, just on the tires instead of the clutch) and the whole drivetrain will get a shock and can be damaged, so again, not a good idea.
All this works pretty much the same way on a bike as well. They use slightly different gearboxes which can shift without using the clutch at high speeds, but the rest is the same
You don’t necessarily have to give it gas, but it does make it easier to get going.
Stalling happens when the engine slows down to a speed (RPM) that isn’t fast enough to get the piston to the next power stroke (when fuel is burned to generate power). The piston already has to work against exhaust and air-fuel pressure, releasing the clutch adds the load of moving the car to this
The clutch is a pair of plates that can be separated by pressing the pedal and releasing it lets them touch again. Releasing further increases the pressure between the plates, which increases friction, making them stick together more. This forces the speed of the engine and the input of the gearbox to match
Each gear in a gearbox has a movement speed associated to an engine speed (RPM) and when you change gear, you change the ratio between those 2 speeds. The input speed comes from the engine, it’s converted to the output speed, which determines how fast the car goes.
With these 3 bits of information, we can put it together:
When the clutch is completely released, the engine and gearbox input speeds are forced to be the same. This results in an output speed that moves the car. If we have a stationary car, which would do 10km/h at idle in first gear, then the moment you drop the clutch, it should instantly be moving at that 10km/h speed. What happens instead is that the resistance coming from the car stops the engine. You can stall in a moving car too, if the engine is forced to turn slower than it needs to reach the next power stroke.
The way slowly releasing the clutch helps is by decreasing the pressure between the clutch plates. This allows them to have a speed difference, essentially converting some of the engine’s power to heat instead of movement. This also means that part of the force that would stop the engine is converted to heat, letting the engine keep turning easier. While the clutch is allowed to slip, the car is less efficient and wears the clutch out, but with normal operation, this wear takes decades to become noticeable. Pressing the gas while getting moving gives more power to the engine, letting you put more load on it but heating the clutch up more in the process (which is fine if you don’t go crazy with the gas). If your engine is more powerful than the grip of your tires, then at high enough RPM, it will be able to handle the clutch being dropped instantly, but in that case the wheels will spin (which also converts mechanical resistance to heat, just on the tires instead of the clutch) and the whole drivetrain will get a shock and can be damaged, so again, not a good idea.
All this works pretty much the same way on a bike as well. They use slightly different gearboxes which can shift without using the clutch at high speeds, but the rest is the same
You don’t necessarily have to give it gas, but it does make it easier to get going.
Stalling happens when the engine slows down to a speed (RPM) that isn’t fast enough to get the piston to the next power stroke (when fuel is burned to generate power). The piston already has to work against exhaust and air-fuel pressure, releasing the clutch adds the load of moving the car to this
The clutch is a pair of plates that can be separated by pressing the pedal and releasing it lets them touch again. Releasing further increases the pressure between the plates, which increases friction, making them stick together more. This forces the speed of the engine and the input of the gearbox to match
Each gear in a gearbox has a movement speed associated to an engine speed (RPM) and when you change gear, you change the ratio between those 2 speeds. The input speed comes from the engine, it’s converted to the output speed, which determines how fast the car goes.
With these 3 bits of information, we can put it together:
When the clutch is completely released, the engine and gearbox input speeds are forced to be the same. This results in an output speed that moves the car. If we have a stationary car, which would do 10km/h at idle in first gear, then the moment you drop the clutch, it should instantly be moving at that 10km/h speed. What happens instead is that the resistance coming from the car stops the engine. You can stall in a moving car too, if the engine is forced to turn slower than it needs to reach the next power stroke.
The way slowly releasing the clutch helps is by decreasing the pressure between the clutch plates. This allows them to have a speed difference, essentially converting some of the engine’s power to heat instead of movement. This also means that part of the force that would stop the engine is converted to heat, letting the engine keep turning easier. While the clutch is allowed to slip, the car is less efficient and wears the clutch out, but with normal operation, this wear takes decades to become noticeable. Pressing the gas while getting moving gives more power to the engine, letting you put more load on it but heating the clutch up more in the process (which is fine if you don’t go crazy with the gas). If your engine is more powerful than the grip of your tires, then at high enough RPM, it will be able to handle the clutch being dropped instantly, but in that case the wheels will spin (which also converts mechanical resistance to heat, just on the tires instead of the clutch) and the whole drivetrain will get a shock and can be damaged, so again, not a good idea.
All this works pretty much the same way on a bike as well. They use slightly different gearboxes which can shift without using the clutch at high speeds, but the rest is the same
#ELI5
The car is at idle. You’re not giving it any gas.
The engine’s output is low, because you’re not giving it gas.
The engine has to keep the air conditioner working, and power steering, power brakes, and generate electricity for the lights, radio … *the engine has WORK to do*.
And it’s able to do only so much work while idling.
Now you let out the clutch, and you’re asking the engine to move the car too! You’re asking it to do more work than before!
But at idle, it doesn’t have any more “oomph”. It’s using up all the work it can produce, to run fan belts, power steering, air conditioner. It can’t move the car forward too!
So you have to give it more gas, which makes it rev higher, which makes it able to do more WORK.
………… Follow-on …………
Take any car (manual or not), and sit in it, with car in park, at idle. Give it no gas. Make sure your air conditioner is OFF.
Listen to the sound of the engine. Maybe there’s a tachometer so you can see the RPMs.
Be very quiet …..
Now turn on the AC.
You might notice that the car is now revving just a teensy bit higher. The RPMs may be going a teensy bit higher.
That’s because the car said “Oh my, Fun-Juice wants to run the air conditioner now too?? I better rev higher all by myself, so that I can do more work.”
#ELI5
The car is at idle. You’re not giving it any gas.
The engine’s output is low, because you’re not giving it gas.
The engine has to keep the air conditioner working, and power steering, power brakes, and generate electricity for the lights, radio … *the engine has WORK to do*.
And it’s able to do only so much work while idling.
Now you let out the clutch, and you’re asking the engine to move the car too! You’re asking it to do more work than before!
But at idle, it doesn’t have any more “oomph”. It’s using up all the work it can produce, to run fan belts, power steering, air conditioner. It can’t move the car forward too!
So you have to give it more gas, which makes it rev higher, which makes it able to do more WORK.
………… Follow-on …………
Take any car (manual or not), and sit in it, with car in park, at idle. Give it no gas. Make sure your air conditioner is OFF.
Listen to the sound of the engine. Maybe there’s a tachometer so you can see the RPMs.
Be very quiet …..
Now turn on the AC.
You might notice that the car is now revving just a teensy bit higher. The RPMs may be going a teensy bit higher.
That’s because the car said “Oh my, Fun-Juice wants to run the air conditioner now too?? I better rev higher all by myself, so that I can do more work.”
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