Re: What circumference did you enter into your Coker cycle computer?
“Cubby01” <firstname.lastname@example.org> wrote:
>No Coker here but an alternative way of measuring. Mark off exactly 100
>meters in a straight line. I have a 50 meter measuring tape that makes this
>fairly easy. Start, noting pedal position, on first mark. Count full pedal
>strokes to end mark. Estimate amount of last rotation. An average
>circumference measure, taking into account rider weight, wheel wobble, etc
>would be 100000mm / rotations. example 100000/36.25=2759mm. If you can
>estimate that last bit to within a quarter rotation your accuracy is within
>0.6% for that wheel size. Much more than meets my needs. I personally just
>do the role it in a straight line next to a meter stick method. I repeat a
>couple times and I put weight on it.
Thanks Cubby! This is an excellent method and description.
For those of us who do want that elusive extra measure of precision, we
could have someone else estimate the final fraction of a rotation by
putting a strip of masking tape on the sidewall parallel to the valve
stem. Doing a flying start, one person could estimate the initial
fractional rotation with respect to the masking tape mark on the tire
and a second could estimate the final fractional rotation.
>Even though you’ve been talking about coker tires that should come out close
>to the same. Measuring down to the mm sounds like overkill. The
>measurements are likely to change by several mm as the tire warms up, cools
>down, wears, goes across different road surfaces, etc.
It truly is overkill for anyone who is primarily interested in a
computer record of their daily and total mileage. However, when one is
interested in serious training for time trials or other racing, it is
very important that their computer be calibrated as precisely as
We should know that riders that demand precision will have to
recalibrate their computer periodically as the tire wears down.
Cubby also makes an interesting point about the circumference changing
as the tire heats up and cools down. Would be interesting to compare
the circumference of a Coker tire at -20 C versus 30 C for example
(could be done in the winter where outside temperatures dip below -20 C
versus the warmest room in a house, 30 C).
Concerning road surfaces: Touring unicyclists may ride on paved,
gravel, sand, clay, etc. Unicyclists doing time trials will likely
restrict themselves to primarily smooth paved surface, which a computer
should accurately measure if precisely calibrated on the same surface.
Cubby, thanks also for your points about temperature related tire
expansion/contraction and varying road surfaces effects on computer
Ken Fuchs <email@example.com>