Brake horsepower
Brake horsepower (bhp) is the measure of an engine's horsepower without the loss in power caused by the gearbox, generator, differential, water pump, and other auxiliary components such as alternator, power steering, and AC compressor. Thus the prefix "brake" refers to where the power is measured: at the engine's output shaft, as on an engine dynamometer. The actual horsepower delivered to the driving wheels is less. An engine would have to be retested to obtain a rating in another system. The term "brake" refers to the original use of a band brake to measure torque during the test (which is multiplied by the engine RPM and a scaling constant to give horsepower).
Si je comprends bien, c'est la même chose que la différence de mesure sur une moto entre la puissance à la roue arrière et la puissance en sortie de boite.
c'est la difference entre la puissance reelle sortie arbre moteur et puissance effective utilisée
la difference est la perte de puissance liée a un frottement (l'eau par ex) ou les differents renvois d'angle