What torque and horsepower mean for cars
 

I'm trying to understand what torque and horsepower are, and what they actually do for a car. Here's what I think I know.

Torque is rotational force. In high school physics we measured force in newtons, but that was for forces in a straight line. As a rotational force, torque is measured in newton meters, or pound feet.

If you use a wrench to turn a nut, and you apply 10 pounds of force at the end of the 1 foot handle, you're applying 10 pounds * 1 foot = 10 pound feet of torque. For a car, the torque is the rotational force applied to the engine's wiener. (What's the technical term?)

Power is a measure of how fast you're getting shit done. It's work / time, or force * distance / time. For cars the unit of power is the horsepower (1 hp = 550 foot pounds per second), and the term horsepower is often used interchangably with power even though one is a unit and one is a concept.

A handy formula relates torque to power:
Power (hp) = torque (lb-ft) * RPM / 5252

That formula works because power is force * distance / time, and torque is force, and RPM is not exactly distance / time, but I guess rotational force has to go with rotations / time?

But what do torque and power mean for a car's performance? I've always heard that torque gets you moving and horsepower keeps you moving, but that doesn't seem right.

It seems like power is what actually moves a car, and torque does nothing for you per se, but is important only because it's a big factor in determining power. A car with more torque can generate the same power at lower RPMs, but a car that allows higher RPMs can generate the same power with less torque.

So at the end of the day, horsepower is all that matters, whether it comes from torque or RPMs. Yes, no, maybe so?

Power equals torque x rpm. You cannot have one without the other except when rpm is zero.
Torquing about which is more important is meaningless; torque and power are 2 sides of the same coin.

having high torque at a given rpm mean you feel the push more

having high power means you end up going faster then the other car in the end. (*not counting aero/weight of the car)

And gearing

Yesssss!!

This is something that is usually not mentioned in these power vs torque threads.

@Johnny Horsepower
It reads like you've done some research. I'm guessing you would have seen a gazillion other posts about this subject.

Yes, aero/weight/gearing are certainly important, just not the focus of this particular thread.

They're definitely related, but I wouldn't say 2 sides of the same coin. Say you have car A and car B. Car A has more peak torque, but car B has more peak horsepower (due to a higher redline). Other things being equal, isn't car B going to accelerate faster and have a higher top speed?

I agree with this part...

...but also having high rpm at a given torque means you feel the push more. So high power means you feel the push more, right?

I have, but I've found them to be confusing and contradictory, and I'm not sure what to believe yet.

Horsepower is how fast you hit the wall; torque is how far you move it.

:popcorn:

You CAN NOT ignore these when trying to figure out how fast a car will accelerate. You just can't. You are trying to reduce a calculation involving several factors down to an A or B scenario and it doesn't work that way.
Horse power and torque are not two isolated things and you can not have acceleration without both AND all the other considerations.

Torque and horsepower are numbers. The bigger the numbers, the faster that car will go.

See how simple that was - :D


humfrz

Yeah, people say that, but then I see things like this: https://www.roadandtrack.com/car-cul...wer-vs-torque/

Sure, those other things are going to make a huge difference. But without some simplifying assumptions, no question could ever be answered. This is confusing enough already for a seemingly simple question.

I think it's reasonable to assume that cars A and B have the same weight, aerodynamics, and gearing, even if that's not quite realistic. (Like more torque might mean a bigger engine, which changes other things.) If that's too much to assume, then OK, let's say this is for entertainment purposes only, to provide a simple illustration of the concepts of power and torque.

If you want the real basics then you received the answer in the first reply to this thread. If you chose to ignore that then you will never get a true grasp of it.

The video in the link you gave explains it all perfectly. If you can't get it from that then I give up.