Horsepower - The Power of the Bike


Despite the fact that anyone who has any enthusiasm for the performance of motorcycles refers to 'horsepower', European regulations say that manufacturers must quote power outputs in kilowatts (or kW), which if you want to compare the output of latest sportsbike to grand dad's old big bike it might be of some use, I suppose... though I doubt the average grand dad wants to know that your latest sportsbike is about eighty times more powerful than his old two-wheeler...

A 'proper' mechanical horsepower is somewhere around 750 Watts (0.75kW) if you want some sort of basis for comparison. While I'm at it, you might see power outputs quoted in PS, DIN, SAE or even CV, so what's that all about? Well, PS is from the German 'pferdestärke' which literally means 'horse power'; CV is an abbreviation of the French 'cheval-vapeur', the Italian 'cavalli vapore', the Spanish 'caballos de vapeur', and the Portuguese 'cavalo-vapor', all of which pretty much translate as 'horse steam'. DIN and SAE are German and American standards, so horsepower quoted as DIN is almost inevitably PS, and if it's quoted in SAE, it's just smaller American horses to make things sound bigger than they actually are.
If you're making comparisons between similar outputs, then you really need to make sure that you're comparing like for like, but the maximum difference between units is somewhere around 85 percent I seem to recall. So while 85 of one unit might be the same as 100 of another, 300 of any of them is always going to be more than 200 of any of the others. That said, some standards don't allow for the fact that the some of the horsepower is used doing things like driving the alternator, water-pump and the gearbox, and only measure horsepower at the crankshaft, while other standards are measured at the driving wheel, telling you how much horsepower there is to actually move the motorcycle along the road. Somewhere around 25 percent of the crankshaft horsepower will be absorbed in driving the transmission and engine ancillaries with most things, which is where 400 horsepower measured at the crank without an alternator isn't necessarily more than 300 horsepower measured at the driving wheel.

So, armed with some idea of who there are all those different numbers and how they stack up against each other, there remains the question of just what is horsepower anyway?
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