Wednesday, April 16, 2008

Metrics Gone Wrong: Horsepower at 100% Throttle

In the April issue of Bike magazine, Simon Hargreaves examines the myth of the dyno. The rise of the the Dynojet Dynamometer provided a cheap, standard way to measure motorcycle horsepower, allowing a common manner to rate the impact of your performance tweak. Roll your bike up to the rollers, and wind it up to full throttle. Moments later, the dyno spits out a pretty graph with torque and horsepower. (I recall a sweaty, restless July night at Texas World Speedway, the motorsport jewel of the Bryan/College Station where my buddy and I parked the VW camper van next to the dyno. Yosh pipes howling through 100% throttle get old after about the 15th carb rejetting, but the dyno truck's jam box pumping out interstitial "Give It Away" got old after the 5th round. )

None the less, Hargreaves cites the problem with a standard measure:

First, higher horsepower figures than the manufacturer next door sells more bikes than him, though - second - higher horsepower figures bring anti-biking legislation closer and closer, despite the fact that - third - accident figures aren't related to increased power, even though - fourth - the performance of your three 160hp models comfortably exceeds the ability of your customer to get anywhere near using it all without crashing.
The answer is measuring 40% and 20% throttle as well. The nebulous corner exit power that was measured only in sphincter tension or nebulous terms like "grunt" and "oomphus" is now a value that can be colored red, blue or green and plotted on a pretty graph. And a telling graph it is, as the GSX-R1000 appears to have dropped power at 20% throttle (to reduce highsideability) while maintaining the pornographic 160hp at top.

So, the top number, the easy number, the number of honorable tradition, means less and less once it is maxed. The tweaks underneath where there, and important. But you are stuck with your gut feeling until you plot it with a pretty blue line.

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