So what is bhp.
BHP is Brake Horse Power. So its clear that its a unit of power.
Now what is power. Power is energy. Or in other words, Power is the rate at which Work is Done.
Power = Force X Velocity
We can strip this down more;
Since Velocity is distance/time,
Power = Force X Distance / Time
So as said earlier, power is the rate at which work is done; And so depends on both
* The Work done
* The Rate at which work is done
This is a key point. A cheetah can claim a Large bhp because it can carry its body at a rate of 110kmphr. And reach there within an incredible 4 seconds; Here its the second factor, the rate, that predominates.
Now the elephant - Its rate may by max 30kmphr. But it can claim a huge bhp too; because the weight it displaces is many many times huge compared to a cheetah. Here the first factor, the work, predominates.
Now in the bike story, we introduce the term Torque.
Torque is nothing but work.
And bhp = torque X rpm.
This does not conflict with the above equations since rpm is equivalent to (1/time).
Now when we say that say shogun puts out 13.8 bhp@8500rpm, what we mean is that the maximum bhp shogun puts out is 13.8, and this happens at 8500 rpm. If you look at the torque-rpm curve of a bike, you can see the Torque peaking at a certian point, then slipping down. This is the peak-torque point, and generally is ensured that this comes close before the Max-bhp point.
This in fact has a solid reason - Both the torque peak and the power peak can be felt by the rider. Now how is that. Basically these two peaks translate to two peak pleasure points which you are acutely aware of when you push a bike through the band. Now all riders need not be aware of both; But both are there.
When you open up the bike and move up the torque curve, the feeling of pleasure you get derives from your tasting the acceleration. This grows to peak as you hit the torque curve. The velocity is not yet a factor here and the pleasure centers are activated purely by acceleration. Now you are past the torque peak and you begin to realize that the pleasure had peaked; Now its gonna drop actually, and it does, a bit. Something has to done abt it so we have set up the bhp peak to follow soon:
Now its the turn of the power to peak; You begin to sample more and more the factor of velocity; And you begin to derive pleasure from both acceleration and velocity - remember the bike is still accelerating though at a lesser rate; its just that the velocity also joins the game. Now you reach another pleasure peak where you derive a maximum kick out of the total response of the bike - to which both velocity and acceleration contribute - this is the peak power point. You feel the first peak as a solid physical forward surge which pulls your arms out of their sockets and slides your bum up the seat; while the second one is a more intricate feeling - what you taste is a total feeling of terrific displacement; You sense that you are covering ground real fast, real quick.
So in other words you rip through the torque band, reach a pleasure high as the torque peaks, continue through the powerband, and hit another peak of pleasure as the bhp peaks.
No wonder people stress the importance of a broad power band...
Once you are past the peak bhp point, acceleration nears zero and the pleasure
you derive is totally from the constant velocity of your bike...