Torque and power ... in simple words?

[Ross]

All right, I give up! Can someone please explain what torque is and what power is in simple words that allow me to understand what the torque and power ratings for a bike actually mean in terms of top speed and acceleration and whatever else they say about the bike?

Many thanks in advance.

[TomL]

I understand that a bike has lots of torque if it pulls from low revs. That is you don't have to be revving the nuts off it for it to pull away smartly. Bigger engines generally have more torque and are easier to ride because they have a big rev range and the revs that you ride at are not so critical.

Smaller engines are not so torquey and have to be in the rev range to perform. They are more peaky. They are more difficult to ride because if you're not in the rev range and you give it a handful nothing much happens and you have to change down and try again. The rev range is very small and is normally just below the maximum revs.

[mutz_nutz]

Torque is a measure of the twisting force generated by the crankshaft and directly relates to accelaration.
Torque is a function of the pressure exerted on the piston by the combustion process, which in turn is related to the compression ratio - the higher the pressure, the higher the torque developed. Think petrol v. Diesel for example.

Power is a direct function of the peak RPM of an engine, thus size for size, a high revving IL4 should generate more power than the lower revving but torquier V-twin with a comparable compression ratio, but develops less torque as the pistons are smaller and less pressure is exerted.
Hope this helps

[Ross]

Thanks to you both!

Okay, given what you both have said, I may have gleaned a little bit more but am more than willing to stand corrected and learn some more:
It seems to me that a higher torque is, in effect, a greater force exerted on a drive shaft or chain cog. The higher the torque, the more effective each piston cycle is at pushing round the shaft drive or chain mechanism. Is this close enough?
On the power side, the higher the revs, the faster the piston cycle and therefore a greater number of turns of shaft or chain cog are achieved in a given time period. Is this correct?
If both the above are true, then a high torque and high revving engine would be the best for acceleration and top speed. Is this true?
I suspect that significant torque and high upper revs make for very high stresses on an engine and frame and that compromises are therefore sought to take account of of engineering materials limits and economics. Is this the reason for a tendency to go down either dominant power (e.g. in-line fours) or dominant torque (e.g. large capacity v-twins) design routes?

[mutz_nutz]

In a nutshell your comments are correct, however in real world terms, the line between high power and torque is becoming blurred by technology such as variable length inlet tracts, which improve airflow into the cyinder at low speeds to improve torque.
Other factors also come into play like rotating masses, gear ratios and overall weight, all of which can have an effect on the performance of a bike.
Ultimately, most road engine designs are a compormise to meet noise, emission, cost and performance requirements...try riding a MotoGP bike at 30 mph on the road!

[tigger]

Basic as I understand it is Torque gives you the acceleration and HP give the top speed.
If you look at most engine power/torque graphs, max hp is at higher revs than max torque. So max acceleration is achieved if you accelerate to just over max hp revs then change up allowing the revs to drop to just below max torque before accelerating again, simple!
Only problem is the closer the two peaks are the quicker you have to be, fractions of a second, hence quick shifters etc.

[gerdipp]

Hello Ross,
i found this explanation in der german Wikipedia:

Drehmoment

Marry Christmas and a happy new year from Germany
Gerhard