Most of the manufacture instructions tell you to measure the wheel radius/diameter/circumference and enter some value related to the measured quantity. This is a good first step.
But you can improve on this. Most countries have a section of
road, usually an expressway, with a marked distance. Sometimes
taxis use this to check their meters. Using this and your trip
meter on your bicycle speedo you can obtain a correction that you
can use to do some Fine-tuning. The longer the distance the
better the result.
At the start of the marked section either reset your trip meter
to zero OR note the trip meter reading. Proceed to the end of the
marked distance and note the final reading. Calculate the correct
value to enter into your speedo by (present value entered) *
(actual distance)/(indicated distance).
OK? But at the end of the distance run my trip meter is just about to roll over another digit... Ah! Say your reading is 5.2, but about to go to 5.3... make your estimated reading 5.25 (or some estimated portion) and use this as your indicated value. Measurement people call this an interpolated reading (i.e. between two marks). The longer the distance the less this interpolation will matter.
You may want to do this adjustment at some speed, just do it using the above methods. The only special thing is that you may not be able to start your trip meter at zero, just note the reading as you pass the road marker and take that way from the final reading...
As speed is distance / time and we have only adjusted the
distance, the speed could be in error due to error in the
measurement of time. But the time, no the rate of time in not
adjustable on the speedo. Ah! But the time rate is governed by a
quartz crystal, and I don't think that will be in error by more
that 1 in 1000, or 1 mph in 1000 mph... no a great concern is
it?
OK, you still want to check. Record the present time indicated
and the actual time. Then come back in about a day and repeat
i.e. record the present time indicated and the actual time. No
you don't need to ride the motorcycle in-between, but if you need
an excuse then ok. Now calculate the (actual time between first
and last record)/(indicated time between first and last record).
Use the same units on both top and bottom, may be minutes is good
enough (1440 in a day). If your clock is perfect you should get
1. If you multiply the calculated value by 100 you have the
answer in percentage... 100% being perfect.
The quartz crystal is sensitive to temperature, so its rate may
vary over the seasons. Just move to a stable climate. Problem
fixed.
If you quote me I would like an acknowledgment.
back to my home page & start again
You can e-mail me at Yahoo. Dated 10 March 2001