Why is it so hard for people to understand torque vs power??
Discussion
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.
RH
Horsepower is calculated from torque (* revs etc.). To "compare" them is absurd.
The problem is perpetuated by journalists (from car mags as well) saying a given engine is "torquey". What they are really trying to convey (but rarely do) is that car X has a lot of power a low revs. How "torquey" is your TDi at 9000rpm? It's not at all as it can't rev that high, let alone produce power there!
The problem is perpetuated by journalists (from car mags as well) saying a given engine is "torquey". What they are really trying to convey (but rarely do) is that car X has a lot of power a low revs. How "torquey" is your TDi at 9000rpm? It's not at all as it can't rev that high, let alone produce power there!
Edited by Dracoro on Monday 16th January 16:22
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.
c7xlg said:
1) A cars acceleration is directly linked to the torque AT THE WHEELS and the mass of the car.
Wrong!!!!!A cars acceleration is linked to the thrust at the wheels (tyre contact patch), which can be calculated from either flywheel torque or flywheel power (multiplied by transmission efficiency) and gearing. As Dracoro has said, torque, horsepower and revs are inter-related and can be multiplied up and down by gearing. To talk about one factor in isolation is almost meaningless.
...but acceleration is not just linked to the thrust at the tyre contact patch and the mass of the car. First you have to subtract the rolling resistance and aerodynamic drag from that thrust; what's left over is what causes you to accelerate - otherwise you'd still be accelerating briskly past your Vmax in accordance with F=MA!
Dracoro said:
Horsepower is calculated from torque (* revs etc.). To "compare" them is absurd.
The problem is perpetuated by journalists (from car mags as well) saying a given engine is "torquey". What they are really trying to convey (but rarely do) is that car X has a lot of power a low revs.
That's an interesting point.The problem is perpetuated by journalists (from car mags as well) saying a given engine is "torquey". What they are really trying to convey (but rarely do) is that car X has a lot of power a low revs.
There was a discussion in the General TVR secion a few months ago about rolling road power readings that had been achieved. Now I'm not that familiar with TVR engine capacities but they are presumably in the 4-5 litres region and typical powers were 250-300BHP.
I didn't want to piss on their chips and mention the modified K Series engine in my ex-Caterham that produced 230bhp from 1800cc.
However it does illustrate how important torque is because my Caterham only produced 150lb.ft whilst those TVRs would have been producing monster torque (translated into thrust at the tyre contact patch) which is what really turns them into the beasts that they are.
I didn't want to piss on their chips and mention the modified K Series engine in my ex-Caterham that produced 230bhp from 1800cc.
However it does illustrate how important torque is because my Caterham only produced 150lb.ft whilst those TVRs would have been producing monster torque (translated into thrust at the tyre contact patch) which is what really turns them into the beasts that they are.
MitchyRS said:
Horsepower is how fast you hit the wall, torque is how far you take the wall with you. Simples
...and revs is how much noise you were making at the time! 
In a simplistic way perhaps, I draw a parallel with volts, amps, and watts. Volts with no amps are useless except for a puny spark, and likewise amps with no volts won't do a lot either. Volts AND amps are watts. Revs of a rubber band motor can be spectacular but wouldn't move a decent sized cat, and torque with no revs might lever a boulder up a bit but no more. Grab hold of a lathe chuck, switch it on, and when you land you'll understand that the revs that the motor rose to combined with the torque that forced you over the lathe bed equate to how far you flew! The there's heat and hotness, aka kilocalories and degrees Centigrade. A spark from a grinder is very high on the Centigrade scale but won't burn you, but a bucket of warm water has far more heat in it. There's so much heat in the Thames even in winter as it passes the Royal Festival Hall (or is the Queen Elizabeth Hall?) that with a clever 'heat lever' (heat pump) a Centigrade degree can be amplified to enough degrees to heat the entire building.
Sam_68 said:
c7xlg said:
1) A cars acceleration is directly linked to the torque AT THE WHEELS and the mass of the car.
Wrong!!!!!A cars acceleration is linked to the thrust at the wheels (tyre contact patch), which can be calculated from either flywheel torque or flywheel power (multiplied by transmission efficiency) and gearing.
"Thrust" at the tyre contact patch is directly linked to torque at the wheel hub, so I would say c7xlg's statement is correct - "A car's acceleration is directly linked to the torque AT THE WHEELS".
Edited by deeen on Monday 16th January 18:32
MrKipling43 said:
Torque: measure of work.
Power: rate of work.
No need for it to be any more complicated than that.
This. All those sayings about winning races or walls or whatever are silly. Both numbers are characteristics of an engine, and both are useless in isolation. Comparing them makes even less sense, since they describe different (albeit linked) properties.Power: rate of work.
No need for it to be any more complicated than that.
deeen said:
...I would say c7xlg's statement is correct - "A car's acceleration is directly linked to the torque AT THE WHEELS".
Go figure out what is happening at Vmax, then....You have lots and lots of torque at the wheel hub/thrust at the tyre contact patch, but strangely, the car isn't accelerating at all.
...all the work (horsepower) being produced by the engine is absorbed by rolling resistance and aerodynamic drag. Acceleration is directly linked to the amount of effort left over after you've subtracted these factors. You can use either torque or power to do the sums - they're inter-related, anyway - but if you've got the gearing right what ultimately matters is the amount of work the engine is capable of doing (ie. horsepower).
Another pre-GCSE go figure question for you... steam engines produce maximum torque at zero rpm: how fast would a steam car accelerate if the engine isn't revolving?
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