Accurate Odometer

On Sun, 13 Feb 2005 08:05:09 +0000, Zog The Undeniable
wrote:

wrote:

My cheap cyclocomputers come up with the same distance for a
15.25 mile daily ride +/ 0.03 miles, or +/- 0.2% accuracy.

I get the same distance to within 1/100 mile when riding to work. It's
always 5.57 miles there and 5.60 miles back. The reason for the
difference is that I have to make a right turn at a roundabout on the
way back, which is the long way round if you're riding on the LH side of
the road.

Dear Zog,

Sounds reasonable.

When my normal route up the north side of the Arkansas River
is too icy, I use the other bank, with all sorts of hills
and curves.

Either way, it turns out to be 6.00 miles from the second
crack in my driveway to the curb at the ticket hut below the
dam.

At first I was suspicious, but then I decided that the gods
may be anal retentive, too.

Carl Fogel

Jobst Brandt wrote:
I don't care if it changes a little with inflation
because the tires hold air to my satisfaction for more than a month.

I'm curious what inner tubes you're using that maintain air pressure that
well. Also, how much pressure do you lose over a month?

Art Harris

Dan wrote:
wrote in message
...

As a cross-check, my $15 Nashbar odometer varies perhpas
0.03 miles on either side of 15.25 miles on my daily ride,
which may say more about how much I swerve and how tight I
cut my corners than it says about the accuracy of the
speedometer.


Carl Fogel

Or variation in tire pressure

Maybe you could rent something like this which is made for measuring
distances:

http://www.engineersupply.com/Produc...=ES181&affid=7

wrote in message
...

Dear Dan,

To cut to the chase . . .

My cheap cyclocomputers come up with the same distance for a
15.25 mile daily ride +/ 0.03 miles, or +/- 0.2% accuracy.

Carl Fogel


Carl-

Repeatability does not guarantee accuracy. Consider a machinist who has some
plastic rulers in his toolbox. He got them for free from salesmen. One day
he uses a ruler to measure a part and determines that it is 11-1/8 inches
long. Every day he measures it and gets the same result. He cannot correctly
report the dimension as 11.125 inches as this would imply that his
measurement is accurate to the nearest 0.001 inch. Your various bike
computers may result in the same distance but are they just measuring
rotations of the same wheel?

To state that the measurement of your ride is accurate to the nearest 0.03
miles, we need to know that your calibration is that accurate. It is ok to
state that your measurement varies buy about 160 feet but probably not ok to
say that your measurement is 15.25 miles. I am willing to accept that a
careful person can get 1% accuracy from a bike computer without
verification. If you want to claim 0.1% accuracy, you need to document
calibration against an equally accurate standard and you will probably need
to record secondary influences - tire pressure before and after ride, speed
during ride, etc.

Using highway mileposts as a calibration standard may be useful but you need
to research the method and accuracy their deployment. Are they horizontal
projection or rolling distance? Center of roadway or center of right of way?

There are PhD's who spend their whole careers studying the accuracy of
measurements.

wrote: (clip) Either way, it turns out to be 6.00
miles from the second crack in my driveway to the curb at the ticket hut
below the dam.
^^^^^^^^^^^^^
If you want to achieve a really accurate measurement, don't neglect to
"zero" your wheel magnet. By this I mean, you must stop on the second crack
in your driveway, and, by hand, position the wheel so the magnet is just
past the sensor. In that same position, reset the digital display to zero,
so they start together. A higher order refinement, in which you actually
calibrate the distance of the magnet past the sensor is probably of only
academic interest. :-)

On Sat, 12 Feb 2005 19:47:30 GMT, "Lloyd Hanning"
may have said:

I need some direction he
I'm a runner, and to do some "active recovery" I bought a used mountain
bike. What I'm looking for is an ACCURATE odometer that I can mark the park
roads with 1/4 mile splits, as the local HS track is becoming off limits.
I've done a search on odometers, and can't find any data as to how accurate
the odometers are. Can some one recommend an odometer/speedometer?

Many digital bike odometers, properly clibrated to the tire
circumference, will give you a result to within 5.28 ft plus or minus
one wheel revolution; they read in thousandths of a mile, plus or
minus one wheel revolution. If you can work in metric, many will read
in 1 meter increments (again, plus/minus). For better accuracy than
that, you need to use a distance wheel (often available at rental tool
outlets, used for estimating construction jobs among other things) or
a long tape measure.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

My cheap cyclocomputers come up with the same distance for a
15.25 mile daily ride +/ 0.03 miles, or +/- 0.2% accuracy.

Carl Fogel

Carl: Over a distance of 15.25 miles, a variation of 158 feet doesn't seem
like more than might be accounted for due to normal minor deviations
during
the ride. For example, do you consistently approach and pass through each
intersection in the exact same manner, regardless of the presence of
traffic
or the condition (color) of the light? Might there be a stop sign you come
up to where, with cross-traffic present, you might make a right turn for a
bit and then cut across when safe to do so?

I can't think of any place where my line varies as much as
three feet to either side, other than when I pass cars in a
20 mph zone on a one-way street through the city park.

It's so ridiculously regular that I've thought that slower
days have led to slightly longer odometer readings and
theorized that at lower speeds, there's more swerving.

Unlike the distance, the scenery varies quite a bit. So does
the wildlife--squirrels...

OK, let's stop right there. On some rides, trying to avoid squirrels alone
might add up to a considerable number of feet!

Just about got nailed by one today. Shot out in front of me, then, as
they're known to do (and please somebody tell me why), once they're a foot
or so clear on the other side, they STOP on a dime and either reverse course
*or* make it appear they're about to.

The amazing thing is how fast they can change direction. The one this
morning... it was so close... I actually notice the tail moving completely
from one direction to the other, instantaneously. Which got me thinking...
do they throw their tails to help flip them in the other direction, or is
the tail following? I suspect the former.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

Hey, Thanks guys, for all your input! What would be interesting is to do an
MSA and specifically a Gage R & R. Now the only thing I have to do is get an
odometer that measures to MM.
Thanks again, you were all helpful!

Lloyd Hanning

"Lloyd Hanning" wrote in message
m...
I need some direction he
I'm a runner, and to do some "active recovery" I bought a used mountain
bike. What I'm looking for is an ACCURATE odometer that I can mark the
park roads with 1/4 mile splits, as the local HS track is becoming off
limits. I've done a search on odometers, and can't find any data as to how
accurate the odometers are. Can some one recommend an
odometer/speedometer?

Thanks

Lloyd Hanning

On Sun, 13 Feb 2005 20:06:06 GMT, "Mike Jacoubowsky"
wrote:

[snip]

Unlike the distance, the scenery varies quite a bit. So does
the wildlife--squirrels...

OK, let's stop right there. On some rides, trying to avoid squirrels alone
might add up to a considerable number of feet!

[snip]

"You talk back."
--Calvin Coolidge on how he finished with White House
visitors by 5pm when his successor as governor of
Massachusetts was still seeing people at 9pm

"You swerve for squirrels."
--Carl Fogel on why some riders see more variation on their
odometers

On Sun, 13 Feb 2005 17:00:58 GMT, "Leo Lichtman"
wrote:


wrote: (clip) Either way, it turns out to be 6.00
miles from the second crack in my driveway to the curb at the ticket hut
below the dam.
^^^^^^^^^^^^^
If you want to achieve a really accurate measurement, don't neglect to
"zero" your wheel magnet. By this I mean, you must stop on the second crack
in your driveway, and, by hand, position the wheel so the magnet is just
past the sensor. In that same position, reset the digital display to zero,
so they start together. A higher order refinement, in which you actually
calibrate the distance of the magnet past the sensor is probably of only
academic interest. :-)

Dear Leo,

I hate to admit it, but . . .

Magnet straight up, just past sensor on fork.

Gives you a slight jump to get rolling before the first
click of the reed switch triggers the sleeping
cyclocomputer.

Naturally the speedometer is zeroed.

I'm sure that this differs from superstition in some crucial
way.

Academically,

Carl Fogel