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Speedo error



Sullivan, Perry writes:
 > 
 > On the average I would say that all of the new bikes have anywhere
 > from +6 to +10 mph error at 70 mph actual [...]. The weird thing is
 > the odometer and trip meter seems to be fairly close.  When I did my
 > SS 1000 my bike odometer read 1040 miles, map blast figured 1034 and
 > the IBA gave me 1030.  So the indicated mileage is closer to actual
 > mileage, than the speed is.

    Bike odometers work by counting wheel revolutions and have the
potential for being quite accurate, variations in tyre diameter with
speed notwithstanding.

    Mechanical speedos have no direct mechanical link to the wheel; a
revolving magnet acts on the needle to pull it around the dial against
the resistance of a spring.  So accuracy depends on the tolerance of the 
spring as well as tyre diameter, the strength of the magnet and probably 
other things.

    On top of all this, in the UK at least speedos are allowed
tolerances of -0% to +10%, that is they're allowed to overread but not
to underread.  This has the "benefit" of letting people think they're
speeding when they're not really.  A completely accurate mechanical
speedo is a rare beast.

    Digital speedos should be very accurate - isn't that what the RS
has?  Any comment from our RS owners?

 > The strange thing is my T - Bird Speedo is right on??

    Sometimes you get lucky...

                Jim
- -- 
       jim@       ,'_            I could almost visualise the 12 foot
  gillespie.org  / -.--.    ___  long crankshaft thrashing around like a
                _\_  ~-.`--'_.-' crazed conger eel in a bath of treacle.
               / /\\    \--'_ \\ 
 '99 Sprint ST \__/ `---'  \__/                         -- Neil Ronketti


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