system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why is torque an important aspect in automobiles, how does it relate to horsepower and top speed?
gpt
Taking a different approach to the other explanations here, explaining it LY5:

You know how inside your car engine, petrol/gas is being burned in lots and lots of big explosions each second?

**"Torque"** is how much one of those explosions is worth. If you were holding it in your hand, how much it would hurt; more petrol exploding is more torque.

For an engine with really big cylinders, each explosion is bigger. For an engine with the *same displacement* but more cylinders, each cylinder is smaller, so each explosion is smaller.

**"Horsepower"** is how many of those explosions you can do every second, multiplied by how strong those explosions are. It's like the total effort your car can do over time, as opposed to how much torque it can deliver instantaneously. That's really all there is to it.

As for **top speed**: first you need to understand air resistance. The faster you go, the more air resistance there is. Like when you're walking, you can't really feel the wind. On your bicycle, you can feel the wind as you go really fast. That's air resistance.

Horsepower is what overcomes air resistance; air resistance is happening all the time while you're driving, so horsepower overcomes it because horse power is in "explosions per second" unlike torque which is "one explosion".

There comes a point, as you go faster, where air resistance and horsepower are the same; horsepower is driving forward, and air resistance is pushing backward, and you stop being able to go any faster. That's your top speed.

When you're pulling tree stumps out of the ground, you don't care how long it takes, you care how hard you can pull each time you drive a little. That's why tractors have lots of torque but no horsepower.

EDIT: And some extra thoughts, LY10:

* For the same displacement, more cylinders means each cylinder is smaller. Because they're smaller, they can spin faster [because there's simply less piston weight to move around]. Talking about motorcycles, because there's lots of good case studies:

* Harleys have two big cylinders. They get lots of torque, but very little horsepower. Those big pistons just can't go very fast [say, redline at 6k rpm]. They make slow "burble burble" noises.

* On the other hand, a four cylinder sportbike delivers very little torque, but you can spin the engine super fast because the pistons are pretty small. That's why sportbikes always ride around sounding like they're ripping the engine out of the casing: they just can't deliver much power to the wheels until you spin them up. [eg, an R6 redlines at 17500 RPM; it's spinning at literally three times the speed of a harley engine].