Speed and fuel consumption, some calculations...
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Thread: Speed and fuel consumption, some calculations...

  1. #1
    Registered User Array michael's Avatar
    Join Date
    May 2005
    Under the radar. Hopefully.
    Honda. Still. Again.

    Speed and fuel consumption, some calculations...

    I've plagiarized this from another (private) list, which may be of some interest.
    (Yes, the author is an engineer. Automotive actually)

    The relationship between fuel economy and speed for the ST1300 will be
    similar to that for other motorcycles of similar power. As speed
    increases, power demand increases exponentially because aerodynamic drag
    is related to the square of velocity. At 70 mph, a typical sport
    touring bike requires about 12.3 horsepower at the rear wheel, which
    translates to about 14.5 hp at the crankshaft after accounting for
    drivetrain and tire loss. At 90 mph, the rear wheel power increases to
    about 25 hp and the crankshaft power is about 29.4 hp.

    Even at 90 mph, the crankshaft power required in only about 20% of rated
    engine power, so the engine is still heavily "throttled" and the
    throttling losses reduce its efficiency to about 0.60 lbs of
    fuel/brake-horsepower-hour. At 70 mph, the engine has even higher
    throttling losses and its efficiency is reduced to about 0.64

    Doing the math, the fuel economy at 70 mph is about 45 mpg and the fuel
    economy at 90 is about 31 mpg. That's representative of steady speed
    cruising over level terrain at sea level with no wind. On a bike with
    an exhaust gas oxygen sensor, fuel economy increases at higher altitudes
    and over slightly rolling terrain. Fuel economy obviously decreases
    with net elevation increases or headwinds.

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  3. #2
    ninja machinist Array Darkcbr's Avatar
    Join Date
    Apr 2004
    RC-51, KX250
    Cool! What I'd like to know is how much of an effect the secondary injectors on my bike have on fuel economy. When I was in alberta I made the trip from Calgary to Lethbridge in exactly two hours at an average speed of about 145-150 km/h. And I got the same fuel mileage that I usually get from stop and go riding. I think I just barely squeezed out 235kms from my tank.

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