Stewart Warner speedometer.

[Lenny]

I just built a 15 speed bike from old parts we had around here. I even
found my old SW speedometer which I had on my 26" Rudge back in the
60's. I installed it on this bike I just built and went out trail
riding with a friend. He brought his GPS along so that we'd make it
out of the woods but as an extra he also clocked our mileage. My
speedo which as I recall used to be dead on the money when it was on
my English bike, is indicating that we traveled farther than his GPS
indicates. Is this due to the fact that my present wheel is slightly
larger than the original? And if so is there any way to either
recalibrate the SW speedo or alter the installation? Thanks, Lenny
Stein

 

[LioNiNoiL_a t_Y a h 0 0_d 0 t_c 0 m]

> My speedo which as I recall used to be dead on the money
> when it was on my English bike, is indicating that we
> traveled farther than his GPS indicates. Is this due to
> the fact that my present wheel is slightly larger than
> the original?

A larger wheel will cause the speedo to read less distance travelled,
not more, because it turns fewer revolutions over the given distance.

--
"Bicycling is a healthy and manly pursuit with much
to recommend it, and, unlike other foolish crazes,
it has not died out." -- The Daily Telegraph (1877)

 

[Werehatrack]

On Tue, 07 Sep 2004 23:39:09 -0700, LioNiNoiL_a t_Y a h 0 0_d 0 t_c 0
m <[email protected]> wrote:

>> My speedo which as I recall used to be dead on the money
>> when it was on my English bike, is indicating that we
>> traveled farther than his GPS indicates. Is this due to
>> the fact that my present wheel is slightly larger than
>> the original?
>
>A larger wheel will cause the speedo to read less distance travelled,
>not more, because it turns fewer revolutions over the given distance.

And the SW may be closer than the GPS in terms of distance that the
wheel rotated through. A GPS produces its results via point-to-point
displacement calculation over the smallest granularity of measurement
space it supports, ignoring squiggles in the path between them; the
speedo sees just the wheel rotations, and ignores direction. The
result will often be different. I don't have a gps, but on the few
occasions that I've ridden with someone who did, its distance
measurement only agreed with speedos closely when the path was
relatively straight.

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