Maths genius required! (Bike related but long)

Discussion in 'UK Motorcycles' started by WavyDavy, Jul 20, 2004.

  1. WavyDavy

    WavyDavy Guest

    I *could* work it out, but can't tax the old brain too much at the moment as
    any brain work might unsettle my current 'unemployed and happy' mindset...

    Anyway, got the missus' R6 it's 4 year service recently and then had the
    thing finally set up on a dyno. It also needed new chain and sprockets so I
    asked the dyno bods to sort that.

    But they didn't get a standard set and the gearbox sprocket is now down by 1

    Although I didn't ask for this to be done and could, therefore, get a std
    size fitted, it's made the R6 everything it always should have been.

    The 98.9bhp (with over 95 from just over 11 to 15,000rpm) now makes the
    front lift on the throttle in 2nd (if you give it beans at 9k...) and it
    pulls strongly all the way through each gear.

    So it's load more fun, if a tad more nervous, to ride. But the R6 speedo is
    driven off the gearbox sprocket.

    So I want to know what kind of mental maths is required to work out actual
    speed.... I can't remember the std front/rear sprocket sizes so am guessing
    at an approximate 7-10% overread. And erring on the high side as I got an
    indicated 180mph yesterday which I know is way way too fast for an R6...

    So, anyway. In a nutshell, what speeds will the speedo be recording at 30,
    40, 60 and 70 mph etc now so I can ensure that when the bikes being ridden
    I/the missus ain't holding up the traffic cos we're well under the limit.


    WavyDavy, Jul 20, 2004
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  2. WavyDavy

    Eiron Guest

    If the standard sprocket is 15 teeth and you have a 14 then your speed
    will be 14/15 or 93.333% of the speedo reading, assuming the speedo was
    accurate to begin with.

    The speedo will read 15/14 or 107.14% of the actual speed.

    At 30 mph the speedo will read 32.14mph
    40, 42.86
    50, 53.57
    60, 64.29
    70, 75
    140, 150

    If the speedo was optimistic to start with, it will be even more so now.

    Better to ask Mr. Plod where the local measured half-mile is
    and calibrate it on that with a stopwatch.
    Eiron, Jul 20, 2004
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  3. WavyDavy

    Dr Zoidberg Guest

    A standard sprocket is apparently 16 teeth so your 15 tooth one will cause
    the speedo to overread by 6.67%
    32 , 43 , 64 , 75

    YZF 600

    "I laugh in the face of danger"

    "Then I hide until it goes away"
    Dr Zoidberg, Jul 20, 2004
  4. WavyDavy

    Eiron Guest

    On the other hand, if the standard front sprocket is 16 teeth
    you can do the calculations yourself....
    Eiron, Jul 20, 2004
  5. WavyDavy

    WavyDavy Guest

    But that means that the 180 *and_still_pulling* was around 168 on the old
    speedo readings..... So it must've been reading high to start with, yeah?
    I hope...
    WavyDavy, Jul 20, 2004
  6. Borrow a GPS and look for a constant speed in a straight line with
    that, check speedo at the given speed and bob's yer uncle.
    Ken McCulloch, Jul 20, 2004
  7. WavyDavy

    Spete Guest

    I'm thick, so I think, since the speedo is connected to the frontwheel, it
    doesn't really matter, does it. It reads the speed from the frontwheel and
    if the bike has to do less revs to get to speed, it's just that.....


    Occasionally, I'll be consistent
    Spete, Jul 20, 2004
  8. WavyDavy

    SteveH Guest

    The clue is in the question.
    SteveH, Jul 20, 2004
  9. WavyDavy

    Spete Guest

    Spete, Jul 21, 2004
  10. WavyDavy

    WavyDavy Guest

    "So it's load more fun, if a tad more nervous, to ride. But the R6 speedo is
    driven off the gearbox sprocket." is my giveaway line in the original post,
    I reckon.....

    WavyDavy, Jul 21, 2004
  11. WavyDavy

    Spete Guest

    Ah, right, missed that bit. As I were then...


    Occasionally, I'll be consistent
    Spete, Jul 21, 2004
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