Torque and RPM relation

[Greg Locock]

justafan, how can you claim torque is (more) fundamental?

P=T*N

T=P/N

N=P/T

are all identical equations except for some algebraic diddling about. None looks more fundamental than another. You always need 2 of the three variables to work out the third.

[bhall II]

A recent addition to my list of favorite quotes:

"Power comes from speed; torque without speed is nothing." ~ Mauro Forghieri

[Just_a_fan]

Greg, I was just being silly and countering Ringo's post

[xpensive]

No, torque is fundamental. Power is derived from it.

Give it a name, I guess most things in life can be labeled "fundamental" if you wish, but engine torque itself has zip to do with a car' performance, that's all power and sometimes power-curve. Give me a decent pipe wrench and I can produce more torque than any Formula 1 engine with my bare hands, but without angular speed it's nothing as Mauro Forghieri was quoted above.

[gruntguru]

http://en.wikipedia.org/wiki/Main_Page

There is a lot of conjecture over which "quantities" are fundamental and which are derived. The link above is the SI interpretation. Note the derivation of torque is ML^2/T^2 and Power is ML^2/T^3. (Mass, Length, Time)

There is no system that considers either Torque or Power to be fundamental.

[Jersey Tom]

A recent addition to my list of favorite quotes:

"Power comes from speed; torque without speed is nothing." ~ Mauro Forghieri

I like that. One of my former coworkers had some good stories working with Mauro back in the day.

[xpensive]

Forghieri's last F1 engine, as I recall, it was at the launch of this gem he made the above quote on why he opted for a V12.



Just imagine if Ron had walked this way rather than listening to Corrado Provera's fairy tales?

[strad]

torque is what gets you off the line and moving
Horsepower is calculated from torque
Torque is the basis of power and the transmission is just a torque multiplier
you do not get a horsepower reading off the dyno you get a torque reading from which you can calculate HP at different RPMs

[xpensive]

Power equals Propulsion force times Speed, which is why you get wheelspin at standstill, the engine torque itself is irrelevant.

Not to be patronizing at all, but there are books on Dynamics that xplains it better than I ever can.

[gruntguru]

Torque is the thing that magically appears (converted from combustion to pressure to force to torque ) at the flywheel end of the crankshaft and increases or decreases as you move down the drivetrain then disappears when it hits the road (converted to force).

Power is the stuff that lurks potentially in the fuel tank (as energy) and becomes power the moment it starts to flow towards the engine. Still measurable at every stage, converting to heat energy, some converting to work and heading off down the driveline, never increasing, always decreasing as little bits get covered to heat. Still there when it hits the road, still measurable as it gets converted to kinetic energy, potential energy and finally heat energy.

Torque is the thing that is useful to know in engines and machines that have wheels and shafts.

Power is the thing that is essential to engines and machines of every kind - whether they be electric motors or linear accelerators, steam locomotive or steam catapult, piston aero engine or rocket engine.

[strad]

obviously none of you are drag racers

[gruntguru]

I run a Jet powered dragster. Zero torque but pretty quick.

[xxChrisxx]

the engine torque itself is irrelevant.

I neg voted you for this on the basis that it's factually wrong for the following reasons.

By saying engine output torque is irrelevant, you are effectively saying we don't care about the shape of the torque curve and by extension we don't care about the shape of the power curve (as the two are intrinsically linked)

As i said in an earlier post; in maths world you are fine to use a power figure and force x speed, as we don't need to worry about fixed gearing. Your tractive effort curve would asymptote at 0rpm and decay away to zero at infinite speed.

All would be well, and you would get a pretty decent, though optimistic, approximation the the car's performance.



When you do need to worry about fixed gearing (such as selecting appropriate ratios and designing gears), the engine torque output (ie the shape of the torque and power curves) becomes very, very relevant.

As you say, power is force X speed. In the real world this force is tractive effort applied at the wheels. The shape of this tractive effort curve is the engine torque curve multiplied by a ratio.

You can also select ratios by using the power curve (though it's less intuitive). You are still considering the shape of the power curve, which by extension you are considering the shape of the torque curve.

[wuzak]

As i said in an earlier post; in maths world you are fine to use a power figure and force x speed, as we don't need to worry about fixed gearing. Your tractive effort curve would asymptote at 0rpm and decay away to zero at infinite speed.

You can work out the tractive force by knowing power and speed, without needing to know the gear ratios or what gear the car is in.

[bhall II]

Oh, for ---'s sake, people, have we forgotten already? Torque is energy!







:-"