P
Paul
Guest
I have been using the cycle computer setting provided in the instruction manual chart for my size
tyres for a while now. Recently whilst checking a couple of routes on a map and computer route
finder I have found that the cycle computer is giving slightly longer distances than actual.
Using the information from Sheldon Brown's article on cycle computers I have come up with a range of
values. My cycle computer requires circumferance in
mm. The tyres are semi-slick with a lightly pimpled centre tread and outer knobs and measure 26x1.95
(53-559), they're pumped to approx. 55psi.
The problem that I'm having is that I am coming up with quite a range of values. I'm not worried
about spot on accuracy but would like to get things as close as possible.
The computer manual's suggested setting is 2089 Using Sheldon Brown's ISO formula gives 2088 Hand
measuring the circ. with a tape measure gives 2070 Hand measuring the diamater and multiplying by
3.14 gives 2070
All these values are pretty close, however when doing a roll out test (marking a point on the ground
and then marking a second one wheel revolution away using the valve as a reference point) I
regularly get a value of 2020 to 2030. The value is pretty similar whether I simply roll the bike or
sit on it at the time.
I appreciate that any of the hand measured approaches have scope for human error and the fact that
the old fabric tape measure might have stretched a bit and that the bike must travel in a completely
straight line for the roll out test but still the difference seems slightly odd.
So my question is, which setting to use?
Thanks for any thoughts
Paul.
tyres for a while now. Recently whilst checking a couple of routes on a map and computer route
finder I have found that the cycle computer is giving slightly longer distances than actual.
Using the information from Sheldon Brown's article on cycle computers I have come up with a range of
values. My cycle computer requires circumferance in
mm. The tyres are semi-slick with a lightly pimpled centre tread and outer knobs and measure 26x1.95
(53-559), they're pumped to approx. 55psi.
The problem that I'm having is that I am coming up with quite a range of values. I'm not worried
about spot on accuracy but would like to get things as close as possible.
The computer manual's suggested setting is 2089 Using Sheldon Brown's ISO formula gives 2088 Hand
measuring the circ. with a tape measure gives 2070 Hand measuring the diamater and multiplying by
3.14 gives 2070
All these values are pretty close, however when doing a roll out test (marking a point on the ground
and then marking a second one wheel revolution away using the valve as a reference point) I
regularly get a value of 2020 to 2030. The value is pretty similar whether I simply roll the bike or
sit on it at the time.
I appreciate that any of the hand measured approaches have scope for human error and the fact that
the old fabric tape measure might have stretched a bit and that the bike must travel in a completely
straight line for the roll out test but still the difference seems slightly odd.
So my question is, which setting to use?
Thanks for any thoughts
Paul.