Computer Calibration Result?

I recently acquired a new cycle computer. Leads broke on the old one.
There was a table in the manual relating tire size and calibration
setting, which I understand to be the distance the wheel travels in mm
in one revolution. The table for the new one had 2146 mm for 700x25
which is what I have. The setting for the old one was 2124 for that
size. I decided to measure it. I set up a piece of masking tape on the
ground along a wall in my garage for a track to follow, and made a mark
with a felt pen on the side of the tire. Then I got on the bike and
lined it up with the tape and had my s.o. make a mark on the tape when
the tire mark was bottom center and then rolled myself along the wall
staying next to the tape, until the tire mark was down again and another
mark was made on the tape. I figured I needed to be on the bike to
account for the flattening of tire due to my weight (tire was at my
usual ridding pressure, 100 psi, I weigh about 180). Anyway I got 2089
mm. This is 2-3% less than those table numbers. Is this a plausible
result? Has anyone else done this and got a similar result? Any problem
with my technique as described?

Mike

Mike McGuire wrote in news:docvh.16297$yx6.4269
@newsread2.news.pas.earthlink.net:
This is 2-3% less than those table numbers. Is this a plausible
result? Has anyone else done this and got a similar result? Any problem
with my technique as described?

Tire widths can vary up to 10% from their nominal size. The difference is
usually not very significant.

On Jan 28, 8:48 pm, Mike McGuire wrote:
Any problem
with my technique as described?

It is better if you measure over two or three revolutions of the wheel
as that will minimize the errors in marking the index points on the
ground. You should also repeat the process enough times that you get
repeatable results within a small margin of error.

Mike McGuire wrote:
I recently acquired a new cycle computer. Leads broke on the old one.
There was a table in the manual relating tire size and calibration
setting, which I understand to be the distance the wheel travels in mm
in one revolution. The table for the new one had 2146 mm for 700x25
which is what I have. The setting for the old one was 2124 for that
size. I decided to measure it. I set up a piece of masking tape on the
ground along a wall in my garage for a track to follow, and made a mark
with a felt pen on the side of the tire. Then I got on the bike and
lined it up with the tape and had my s.o. make a mark on the tape when
the tire mark was bottom center and then rolled myself along the wall
staying next to the tape, until the tire mark was down again and another
mark was made on the tape. I figured I needed to be on the bike to
account for the flattening of tire due to my weight (tire was at my
usual ridding pressure, 100 psi, I weigh about 180). Anyway I got 2089
mm. This is 2-3% less than those table numbers. Is this a plausible
result? Has anyone else done this and got a similar result? Any problem
with my technique as described?

Good methodology and, yes, that's a reasonable number.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Mike McGuire wrote:
I recently acquired a new cycle computer. Leads broke on the old one.
There was a table in the manual relating tire size and calibration
setting, which I understand to be the distance the wheel travels in mm
in one revolution. The table for the new one had 2146 mm for 700x25
which is what I have. The setting for the old one was 2124 for that
size. I decided to measure it. I set up a piece of masking tape on the
ground along a wall in my garage for a track to follow, and made a mark
with a felt pen on the side of the tire. Then I got on the bike and
lined it up with the tape and had my s.o. make a mark on the tape when
the tire mark was bottom center and then rolled myself along the wall
staying next to the tape, until the tire mark was down again and another
mark was made on the tape. I figured I needed to be on the bike to
account for the flattening of tire due to my weight (tire was at my
usual ridding pressure, 100 psi, I weigh about 180). Anyway I got 2089
mm. This is 2-3% less than those table numbers. Is this a plausible
result? Has anyone else done this and got a similar result? Any problem
with my technique as described?

Mike


I think 2089 mm is a little on the low side, but within 1%. I measured
my Michelin Pro Race 25 mm tire and the number 2115 mm came up.
Your method is OK. Do some more runs and average the results. I prefer
some touch up paint on the tire. The paint leave marks on the floor. I
find this more convenient.

Lou
--
Posted by news://news.nb.nu (http://www.nb.nu)

In article
.net
,
Mike McGuire wrote:

I recently acquired a new cycle computer. Leads broke on the old one.
There was a table in the manual relating tire size and calibration
setting, which I understand to be the distance the wheel travels in mm
in one revolution. The table for the new one had 2146 mm for 700x25
which is what I have. The setting for the old one was 2124 for that
size. I decided to measure it. I set up a piece of masking tape on the
ground along a wall in my garage for a track to follow, and made a mark
with a felt pen on the side of the tire. Then I got on the bike and
lined it up with the tape and had my s.o. make a mark on the tape when
the tire mark was bottom center and then rolled myself along the wall
staying next to the tape, until the tire mark was down again and another
mark was made on the tape. I figured I needed to be on the bike to
account for the flattening of tire due to my weight (tire was at my
usual ridding pressure, 100 psi, I weigh about 180). Anyway I got 2089
mm. This is 2-3% less than those table numbers. Is this a plausible
result? Has anyone else done this and got a similar result? Any problem
with my technique as described?

Plausible. Technique as described is faultless. What is
the tire pressure and your weight? Tire pressure
difference can generate a 20 mm difference. If you are
150 lb and running 120 psi, I would recommend you redo
the measurement and rethink all the details or your
procedure. Measure again anyway and see if your number
is reproducible.

--
Michael Press

In article
.net
,
Mike McGuire wrote:

I recently acquired a new cycle computer. Leads broke on the old one.
There was a table in the manual relating tire size and calibration
setting, which I understand to be the distance the wheel travels in mm
in one revolution. The table for the new one had 2146 mm for 700x25
which is what I have. The setting for the old one was 2124 for that
size. I decided to measure it. I set up a piece of masking tape on the
ground along a wall in my garage for a track to follow, and made a mark
with a felt pen on the side of the tire. Then I got on the bike and
lined it up with the tape and had my s.o. make a mark on the tape when
the tire mark was bottom center and then rolled myself along the wall
staying next to the tape, until the tire mark was down again and another
mark was made on the tape. I figured I needed to be on the bike to
account for the flattening of tire due to my weight (tire was at my
usual ridding pressure, 100 psi, I weigh about 180). Anyway I got 2089
mm. This is 2-3% less than those table numbers. Is this a plausible
result? Has anyone else done this and got a similar result? Any problem
with my technique as described?

One way to improve the method is to put masking tape on
the wheel, a piece of tape on the ground, match the
edges of the masking tape exactly, roll out, then have
your laboratory assistant put a piece of tape on the
ground to match the registration edge of the tape on
the wheel.

--
Michael Press

On Tue, 30 Jan 2007 21:27:25 GMT, Michael Press
wrote:

In article
k.net
,
Mike McGuire wrote:

I recently acquired a new cycle computer. Leads broke on the old one.
There was a table in the manual relating tire size and calibration
setting, which I understand to be the distance the wheel travels in mm
in one revolution. The table for the new one had 2146 mm for 700x25
which is what I have. The setting for the old one was 2124 for that
size. I decided to measure it. I set up a piece of masking tape on the
ground along a wall in my garage for a track to follow, and made a mark
with a felt pen on the side of the tire. Then I got on the bike and
lined it up with the tape and had my s.o. make a mark on the tape when
the tire mark was bottom center and then rolled myself along the wall
staying next to the tape, until the tire mark was down again and another
mark was made on the tape. I figured I needed to be on the bike to
account for the flattening of tire due to my weight (tire was at my
usual ridding pressure, 100 psi, I weigh about 180). Anyway I got 2089
mm. This is 2-3% less than those table numbers. Is this a plausible
result? Has anyone else done this and got a similar result? Any problem
with my technique as described?

This works even better if you do it for more than one revolution..
For instance measure out and do it for ten revs..
I have a measured 100 feet on the road in front of my house
and by counting the revs to the nearest turn, I can reduce the
possible error even further..

Bob

Mike McGuire wrote:

There was a table in the manual relating tire size and calibration
setting, which I understand to be the distance the wheel travels in mm
in one revolution. The table for the new one had 2146 mm for 700x25

Here's what I did: I put tape (non-stretching type) around the
wheel and cut it off at the exact length. Then take the tape off,
put it on the ground (some flat surface) and measure its length.
It was interesting to see how different the results were for
different wheels/tires.

Bob Flumere wrote:
On Tue, 30 Jan 2007 21:27:25 GMT, Michael Press
wrote:

In article
nk.net
,
Mike McGuire wrote:

I recently acquired a new cycle computer. Leads broke on the old one.
There was a table in the manual relating tire size and calibration
setting, which I understand to be the distance the wheel travels in mm
in one revolution. The table for the new one had 2146 mm for 700x25
which is what I have. The setting for the old one was 2124 for that
size. I decided to measure it. I set up a piece of masking tape on the
ground along a wall in my garage for a track to follow, and made a mark
with a felt pen on the side of the tire. Then I got on the bike and
lined it up with the tape and had my s.o. make a mark on the tape when
the tire mark was bottom center and then rolled myself along the wall
staying next to the tape, until the tire mark was down again and another
mark was made on the tape. I figured I needed to be on the bike to
account for the flattening of tire due to my weight (tire was at my
usual ridding pressure, 100 psi, I weigh about 180). Anyway I got 2089
mm. This is 2-3% less than those table numbers. Is this a plausible
result? Has anyone else done this and got a similar result? Any problem
with my technique as described?

This works even better if you do it for more than one revolution..
For instance measure out and do it for ten revs..
I have a measured 100 feet on the road in front of my house
and by counting the revs to the nearest turn, I can reduce the
possible error even further..

Bob

Find mile markers and use them. I have a stretch of about 8 miles w/
markers every mile. If the computer says you've done more than a mile
when you hit the marker increase circumference. You can get it so you
can pick a tire model/size, consider the pressure (I vary according to
type of ride, and whether I'm sore) and the tire wear and know exactly
how to set the computer. My computer measures by 1/100'th, and in 8
miles I can set it so I'm within about 2/100'ths mile, which is what,
about 2/800'th (=.0025) or about .25% accuracy

Bill Westphal