Accurate Odometer

Jobst Brandt said:

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 said:

<[email hidden]> wrote in message
news:[email hidden]...
<>

Quoted message said:

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.

<>

Quoted message said:

Carl Fogel

Or variation in tire pressure

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

http://www.engineersupply.com/ProductInfo.aspx?productid=ES181&affid=7

<[email hidden]> 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 here:
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.

Quoted message said:

Quoted message said:

Quoted message said:

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?

Quoted message said:

Quoted message said:

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.

Quoted message said:

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.

Quoted message said:

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" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

I need some direction here:
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

Leo Lichtman said:

<[email hidden]> 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

Carl Fogel said:

Quoted message said:

Quoted message said:

>> As a cross-check, my $15 Nashbar odometer varies perhaps 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.

Quoted message said:

Quoted message said:

Quoted message said:

> Or variation in tire pressure

Quoted message said:

Quoted message said:

Quoted message said:

Possibly tire pressure is involved, but unlikely, since the tiny
odometer variation doesn't seem to go in one direction.

Quoted message said:

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Quoted message said:

That is, I don't see my distance slowly increasing (or decreasing)
until I remember to pump my tires up again.

Quoted message said:

Quoted message said:

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The variation could also be due to weight changes, since the
standard Fogel often varies by several chocolate doughnuts.

Quoted message said:

Quoted message said:

Don't rely on others reports if you don't believe them. Just measure
the rollout distance with different inflation pressures on your own
bicycle. I have done it and it isn't just a millimeter. I'm
satisfied that 2093mm is good enough for my Avocet 700-25 tires at
average inflation. I don't care if it changes a little with inflation
because the tires hold air to my satisfaction for more than a month.

Quoted message said:

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Many posters here on rec.bicycles.tech warn of the dangerous
inaccuracy of measuring an unloaded wheel, but I've never seen a
post that mentioned any measured difference in tire circumference
between a loaded and an unloaded bike. (Indeed, the warnings often
fail to mention which way they think the loading affects the
outcome.)

Quoted message said:

Quoted message said:

What dangers have been reported? As inflation pressure decreases, so
does the rollout distance for one revolution. As I pointed out, when
driving a car over Botts Dots on roads you'll notice the slamming
effect get harsher with increasing speed. That is because the change
in rolling radius causes a momentary acceleration of the wheel that
through inertia cannot occur at higher speeds as easily. Therefore,
the slamming effect bends wheel suspension. The bumps do not get
larger nor does wheel bounce but the the rolling radius changes almost
instantaneously. Since most car tires are radials (with a constant
circumference belt), I find that a dramatic demonstration of rolling
radius.

Quoted message said:

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I wouldn't be surprised if the difference was more theoretical than
measurable, but it would fun if someone posted the results of some
careful loaded and unload tire measurements.

Quoted message said:

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Be surprised!

Quoted message said:

Er, you need to read more carefully. Your unreported "dangers" are
not the same as my rather obviously tongue-in-cheek "dangerous
inaccuracy."

Quoted message said:

I'd be more surprised if you were to include the figures that you
say are dramatic. I can't even tell from your post whether you are
saying that the loaded tire produces a larger or smaller
circumference. I'd be willing to believe your figures if you'd
simply post them.

Quoted message said:

You find 2093mm a good average figure for your tires, presumably
measured loaded. What was the unloaded measurement? It "isn't just
a millimeter."

As I corrected in a followup. That was a typo. It is 2096mm.

Quoted message said:

If you reply with a 4-character post, it will be the first time that
I know of an actual difference appearing in this newsgroup.

Quoted message said:

I hope it's not a secret.

As I said, you should be aware of this difference if you measure
rollout distance. The difference per psi varies with weight of rider,
riding position and tire cross section. With my tires in my most
common position, hands on the bar tops (with drop bars), the
difference is 20mm reducing inflation pressure from my usual 100psi to
80psi. I took those pressures because they represent the limit with
which I ride and because it gives a repeatable and easily measured
distance.

The Botts Dots experiment should be obvious the next time you are on a
road that allows speeds up to 65mph. That these accelerations are
large are shown by the tire rubber that leaves skid marks in the
process. It is also why Elbert Botts invented the significant part of
these lane markers, the adhesive. Previously any glued devices were
readily knocked loose. It was his research in the adhesive that made
them possible.

http://www.dot.ca.gov/hq/paffairs/about/botts.htm

The first significant application of these lane markers was on
"Hospital Curve" on HWY101 in San Francisco, a long relatively sharp
curve for an 8-lane freeway around San Francisco General Hospital that
in wet weather, especially at night, was a challenge to not drift into
other lanes, the road stripes being invisible in the wet glare. There
were many serious crashes at that curve that did not have a median nor
a dividing crash-wall. Today, it is hard to visualize how drives
managed before Botts Dots.

http://tinyurl.com/5brzg

Jobst Brandt
[email hidden]

Arthur Harris said:

Quoted message said:

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

Quoted message said:

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?

Any of the Specialized, Trek, Avocet, etc tubes that are labeled
700-28 or thereabouts. These are regular black butyl rubber and look
like they are made by the same supplier. I don't buy ultra light
tubes or ones that are several sizes smaller than the tire inside
cross section.

It all depends on what you find important for your ride.

Jobst Brandt
[email hidden]

On Mon, 14 Feb 2005 05:47:45 GMT,
[email hidden] wrote:

[snip]

Quoted message said:

With my tires in my most
common position, hands on the bar tops (with drop bars), the
difference is 20mm reducing inflation pressure from my usual 100psi to
80psi.

[snip]

Dear Jobst,

So with you sitting on the bike, your front 700c x 25 Avocet
rolls a measured 2096 mm in one spin at 80 psi, right?

Just to be sure that I'm following you, this is 20 mm less
than the same tire's single spin of 2116 mm with no rider,
just the bike rolling along a smooth floor, and the same 80
psi, a roughly 1% difference?

I've never seen any details, so I'm quite interested. If I
missed any details or have them wrong, please let us know.

Thanks,

Carl Fogel

Carl Fogel said:

Quoted message said:

With my tires in my most common position, hands on the bar tops
(with drop bars), the difference is 20mm reducing inflation
pressure from my usual 100psi to 80psi.

Quoted message said:

So with you sitting on the bike, your front 700c x 25 Avocet rolls a
measured 2096 mm in one spin at 80 psi, right?

Wrong. I said it measures 2096mm at 100psi and 20mm shorter (=2076mm)
at 80psi. I thought it was obvious that wheel rolling radius is
smaller under lower inflation pressure or for that matter, greater
load with constant inflation pressure rather than greater.

Quoted message said:

Just to be sure that I'm following you, this is 20 mm less than the
same tire's single spin of 2116 mm with no rider, just the bike
rolling along a smooth floor, and the same 80 psi, a roughly 1%
difference?

Quoted message said:

I've never seen any details, so I'm quite interested. If I
missed any details or have them wrong, please let us know.

You travel a shorter distance per wheel revolution, the closer
the axle is to the road (wheel radius).

Have you measured rollout distance to calibrate a Cyclometer?

Jobst Brandt
[email hidden]

RonSonic said:

I've learned to more or less aim for the squirrel. That little dance they do is
too unpredictable to anticipate, as it should be given the many millions of
years they've been working on it. On the other hand I feel I can trust them to
get out of my way, a thing they wish even more ardently than I. So I aim for
the point where he starts his juke maneauver. My thinking is that the squirrel
is going to act on the assumption that you are trying to get him, reasonable
enough at his end of the food chain, therefor he will act to avoid that, so if I
aim for him then we are both working from the same playbook.

Pretty much my philosophy as well, but I look at them like railroad
tracks - you want to be vertical and run over the things perpendicularly
with a good grip on the bars but not tense. I've rolled over two
squirrels and although they made some funny sounds, they both ran away
afterward with little sign of injury.

Much more likely to go down if you run over a snake in my vicarious
experience.
--
My bike blog:
http://diabloscott.blogspot.com/

On Mon, 14 Feb 2005 19:06:51 GMT,
[email hidden] wrote:

[snip]

Dear Jobst,

Let's try one more time.

You have an Avocet 700c x 25 front tire, right?

What does it measure at 100 psi with you on the bike?
a) 2116 mm
b) 2113 mm
c) 2096 mm
d) 2093 mm
e) 2076 mm
f) 2073 mm
g) other

What does it measure at 100 psi with no rider?
a) 2116 mm
b) 2113 mm
c) 2096 mm
d) 2093 mm
e) 2076 mm
f) 2073 mm
g) other

What does it measure at 80 psi with you on the bike?
a) 2116 mm
b) 2113 mm
c) 2096 mm
d) 2093 mm
e) 2076 mm
f) 2073 mm
g) other

What does it measure at 80 psi with no rider?
a) 2116 mm
b) 2113 mm
c) 2096 mm
d) 2093 mm
e) 2076 mm
f) 2073 mm
g) other

Carl Fogel