Why is it so hard for people to understand torque vs power??
Discussion
Just reading the M-diesel thread and it still amazes me how so many people who one assumes to think of themselves as 'into' cars can't understand the relationships between torque, power, acceleration and topspeed.
My physics education stopped at A-level but to me it is pretty obvious in simple terms that:
1) A cars acceleration is directly linked to the torque AT THE WHEELS and the mass of the car.
2) A cars top-speed is directly linked to the engines power and the drag (air resistance primarily). (this assume the gearing is such that the engine power is limiting factor.. ie not running into rev limiter).
So why do so many people see a large engine torque figure and forget to ask at what revs it is produced? You need to know this to guestimate the torque at the wheels.
For example, if you installed two engines with the following figures in the same car, with gearing adjusted appropriately:
A) Max torque of 200lb/ft in an engine range of 2000-4000 rpm
B) Max torque of 100lb/ft in an engine range of 4000-8000 rpm
You'd end up with a car that accelerates at exactly the same rate. It is just that the engine in car B will be revving twice as fast, but will have gearing 'half as short' to allow for it.
Why do so many people find this so hard to understand?
My physics education stopped at A-level but to me it is pretty obvious in simple terms that:
1) A cars acceleration is directly linked to the torque AT THE WHEELS and the mass of the car.
2) A cars top-speed is directly linked to the engines power and the drag (air resistance primarily). (this assume the gearing is such that the engine power is limiting factor.. ie not running into rev limiter).
So why do so many people see a large engine torque figure and forget to ask at what revs it is produced? You need to know this to guestimate the torque at the wheels.
For example, if you installed two engines with the following figures in the same car, with gearing adjusted appropriately:
A) Max torque of 200lb/ft in an engine range of 2000-4000 rpm
B) Max torque of 100lb/ft in an engine range of 4000-8000 rpm
You'd end up with a car that accelerates at exactly the same rate. It is just that the engine in car B will be revving twice as fast, but will have gearing 'half as short' to allow for it.
Why do so many people find this so hard to understand?
I hope this is right because I'm sticking my head out here but the best terminology I use to describe it to people is it's like a spanner.
Your hand and arm is how much power the spanner has when you twist it and the torque is where you place your hand on the spanner, either further away or closer to the pivot point.
Your hand and arm is how much power the spanner has when you twist it and the torque is where you place your hand on the spanner, either further away or closer to the pivot point.
kambites said:
c7xlg said:
A) Max torque of 200lb/ft in an engine range of 2000-4000 rpm
B) Max torque of 100lb/ft in an engine range of 4000-8000 rpm
Because they are producing the same power, which is what actually matters. B) Max torque of 100lb/ft in an engine range of 4000-8000 rpm
As an example, my mother drives a diesel. I was with her driving my father's petrol (with 50% more power) and she changed gear at the same RPM. I'm sure if you asked her she would say her car is "easier" to drive at a given acceleration rate. To make the petrol move optimally you have to use an extra 3000rpm. Many people think higher RPM is more work/aggressive.
Personally I don't know why, power is power at whatever RPM.
DanielC4GP said:
I hope this is right because I'm sticking my head out here but the best terminology I use to describe it to people is it's like a spanner.
Your hand and arm is how much power the spanner has when you twist it and the torque is where you place your hand on the spanner, either further away or closer to the pivot point.
No, the torque is how much force you can exert on the spanner, power is how quickly you can repeatedly apply that force.Your hand and arm is how much power the spanner has when you twist it and the torque is where you place your hand on the spanner, either further away or closer to the pivot point.
MrKipling43 said:
DanielC4GP said:
I hope this is right because I'm sticking my head out here but the best terminology I use to describe it to people is it's like a spanner.
Your hand and arm is how much power the spanner has when you twist it and the torque is where you place your hand on the spanner, either further away or closer to the pivot point.
No, the torque is how much force you can exert on the spanner, power is how quickly you can repeatedly apply that force.Your hand and arm is how much power the spanner has when you twist it and the torque is where you place your hand on the spanner, either further away or closer to the pivot point.
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