Accurate calibration of cycle computers/cyclometers

Accurate calibration of cycle computer

I measure the distance convered by several revolutions of the wheel
that I am calibrating. Make a scratch mark on the surface with the
valve stem at the bottom of the wheel. Make several revolutions of
the wheel and make another scratch mark with the stem at the bottom
again. I usually use 10 wheel revolutions. Measure this distance and
record it. If the distance was measured in feet, you usually have to
convert it to centimeters to use it in setting your wheel
circumferance. First, find your wheel circumferance by dividing the
distance by the number of wheel revolutions. Then multiply this
answer 30.48 -- this will be the number you use to set the wheel
size. Some cyclocomputers require different inputs for KPH or MPH. -
If you need to use a conversion factor to change from KPM to MPH,
simply divide the kilometer wheel size number by 1.61 - this should
give you speed and distance in miles instead of kilometers.
The tables included with bicycle electronic speedometers work pretty
well, but I like to calibrate them accurately, so I inflate my tires
to working pressure and sit on the bike while doing the wheel
measurements so that they will be more typical of actual operation.

"Dex" wrote in message
news:1122470159.70c6ed5bb0271305fb5d1b10abb65485@t eranews...
Accurate calibration of cycle computer

I measure the distance convered by several revolutions of the wheel
that I am calibrating. Make a scratch mark on the surface with the
valve stem at the bottom of the wheel. Make several revolutions of
the wheel and make another scratch mark with the stem at the bottom
again. I usually use 10 wheel revolutions. Measure this distance and
record it. If the distance was measured in feet, you usually have to
convert it to centimeters to use it in setting your wheel
circumferance. First, find your wheel circumferance by dividing the
distance by the number of wheel revolutions. Then multiply this
answer 30.48 -- this will be the number you use to set the wheel
size. Some cyclocomputers require different inputs for KPH or MPH. -
If you need to use a conversion factor to change from KPM to MPH,
simply divide the kilometer wheel size number by 1.61 - this should
give you speed and distance in miles instead of kilometers.
The tables included with bicycle electronic speedometers work pretty
well, but I like to calibrate them accurately, so I inflate my tires
to working pressure and sit on the bike while doing the wheel
measurements so that they will be more typical of actual operation.

Do some cyclometers have more than one digit of accuracy? My Cateye only has
a single digit to the right of the decimal. I think there is going to be a
1% tolerance at best.





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bent_pilot wrote:

Do some cyclometers have more than one digit of accuracy? My Cateye
only has
a single digit to the right of the decimal. I think there is going to
be a 1% tolerance at best.

Cateye Astrale can be done to the nearest mm, as can the Trek Incite 11
which I have on my MTB after the Astrale which used to live there went to
sleep with the fishes. At the bottom of the canal. The Mity, however, can
only be set to the nearest cm. Don't know about any others, as it's been
ages since I've used anything else.

--
Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
A complimentary biro(tm) is /not/ to be sniffed at.

"Dave Larrington" wrote in message
...
bent_pilot wrote:

snippage

Cateye Astrale can be done to the nearest mm, as can the Trek Incite 11
which I have on my MTB after the Astrale which used to live there went to
sleep with the fishes. At the bottom of the canal.
--
Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
A complimentary biro(tm) is /not/ to be sniffed at.



I certainly hope you applied for the proper licenses for adding to the
detritis at the bottom of the canal.



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Dex wrote:
Accurate calibration of cycle computer

I measure the distance convered by several revolutions of the wheel
that I am calibrating. Make a scratch mark on the surface with the
valve stem at the bottom of the wheel. Make several revolutions of
the wheel and make another scratch mark with the stem at the bottom
again. I usually use 10 wheel revolutions. Measure this distance and
record it. If the distance was measured in feet, you usually have to
convert it to centimeters to use it in setting your wheel
circumferance. First, find your wheel circumferance by dividing the
distance by the number of wheel revolutions. Then multiply this
answer 30.48 -- this will be the number you use to set the wheel

Where does this number come from? The conversion I use is:
millimeters = Inches * 2.54

A 20 inch wheel should be in the range of 1400 - 1500 if your cyclometer takes
4 digits. If it only uses 3 digits it would be 140 - 150, and I'd toss it to
get a cyclometer that is some accuracy, not just a guess at speed and distance.

mike

"Mike" wrote in message
link.net...
Dex wrote:
Accurate calibration of cycle computer

I measure the distance convered by several revolutions of the wheel
that I am calibrating. Make a scratch mark on the surface with the
valve stem at the bottom of the wheel. Make several revolutions of
the wheel and make another scratch mark with the stem at the bottom
again. I usually use 10 wheel revolutions. Measure this distance and
record it. If the distance was measured in feet, you usually have to
convert it to centimeters to use it in setting your wheel
circumferance. First, find your wheel circumferance by dividing the
distance by the number of wheel revolutions. Then multiply this
answer 30.48 -- this will be the number you use to set the wheel

Where does this number come from? The conversion I use is:
millimeters = Inches * 2.54

A 20 inch wheel should be in the range of 1400 - 1500 if your cyclometer
takes 4 digits. If it only uses 3 digits it would be 140 - 150, and I'd
toss it to get a cyclometer that is some accuracy, not just a guess at
speed and distance.

mike


A mm=1"/25.5 (.03937"/mm) so inches*25.4=mm. A centimeter is 10 mm,
cm*2.54=inches. These conversions come from Machinery's Handbook. Where do
your numbers come from, Mike? Either you made a typo, or your values are off
by a factor of 10. Dex, what's with the 30.48???



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"bent_pilot" wrote in message
...

"Mike" wrote in message
link.net...
Dex wrote:
Accurate calibration of cycle computer

I measure the distance convered by several revolutions of the wheel
that I am calibrating. Make a scratch mark on the surface with the
valve stem at the bottom of the wheel. Make several revolutions of
the wheel and make another scratch mark with the stem at the bottom
again. I usually use 10 wheel revolutions. Measure this distance and
record it. If the distance was measured in feet, you usually have to
convert it to centimeters to use it in setting your wheel
circumferance. First, find your wheel circumferance by dividing the
distance by the number of wheel revolutions. Then multiply this
answer 30.48 -- this will be the number you use to set the wheel

Where does this number come from? The conversion I use is:
millimeters = Inches * 2.54

A 20 inch wheel should be in the range of 1400 - 1500 if your cyclometer
takes 4 digits. If it only uses 3 digits it would be 140 - 150, and I'd
toss it to get a cyclometer that is some accuracy, not just a guess at
speed and distance.

mike


A mm=1"/25.5 (.03937"/mm) so inches*25.4=mm. A centimeter is 10 mm,
cm*2.54=inches. These conversions come from Machinery's Handbook. Where
do
your numbers come from, Mike? Either you made a typo, or your values are
off
by a factor of 10. Dex, what's with the 30.48???



There are 30.48 cm in a foot (12 * 2.54).

Jerry

This thread is timely for me because I just got in from doing a roll
out for my ScooterBike CLWB (16 x 1.75 front) to fit it for a new
computer. I'll post the results here in case it helps someone else. I
marked the start and rolled out 4 revolutions of the front tire
(sitting on the bike). I repeated the roll out 3 times and it came out
to 196 inches per roll out. So, one revolution comes out to: 196 / 4 =
49). 49 inches x 25.4 = 1244.6 mm. Let's call it 1245 even.

I use White-out on the concrete garage floor

"Dex" wrote in message
news:1122470159.70c6ed5bb0271305fb5d1b10abb65485@t eranews...
Accurate calibration of cycle computer

I measure the distance convered by several revolutions of the wheel
that I am calibrating. Make a scratch mark on the surface with the
valve stem at the bottom of the wheel. Make several revolutions of
the wheel and make another scratch mark with the stem at the bottom
again. I usually use 10 wheel revolutions. Measure this distance and
record it. If the distance was measured in feet, you usually have to
convert it to centimeters to use it in setting your wheel
circumferance. First, find your wheel circumferance by dividing the
distance by the number of wheel revolutions. Then multiply this
answer 30.48 -- this will be the number you use to set the wheel
size. Some cyclocomputers require different inputs for KPH or MPH. -
If you need to use a conversion factor to change from KPM to MPH,
simply divide the kilometer wheel size number by 1.61 - this should
give you speed and distance in miles instead of kilometers.
The tables included with bicycle electronic speedometers work pretty
well, but I like to calibrate them accurately, so I inflate my tires
to working pressure and sit on the bike while doing the wheel
measurements so that they will be more typical of actual operation.

bent_pilot wrote:

I certainly hope you applied for the proper licenses for adding to the
detritis at the bottom of the canal.

Yes, and sadly when British Waterways discovered that my bike does not
currently have a permanent mooring, they charged me extra for a Continuous
Cruising one :-)

--
Dave Larrington - http://www.legslarry.beerdrinkers.co.uk/
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