Cayeye tire size chart for cycle computers

Quoted message said:

Rik O'Shea said:

Yes, I've always used the tire rollout method when calibrating my
cycle computer but today out of curiosity I took a straw poll among
some of the commuter friends at work who use a cycle computer and
guess what, 4/4 used the chart that came with their cycle computer!

Yes? How large is your sample, and what conclusion do you expect
others to draw from that?

He states that fact: sample size of 4.

Jasper

Benjamin Lewis said:

I get significantly better precision in my rollout measurements than my
cycle computer allows (I can only enter rim circumference to the nearest
centimeter, but can accurately measure to within a mm or so). I could, of
course, use this additional measurement precision to obtain a corrective
factor for my computer's readout, but readings within the +/- 0.25% accuracy
given by the 1 cm calibration limit are already good enough for my
purposes.

OK, if you were to ride a course of a mile or so that you were certain
had been precisely measured, and you found your computer's distance
function to be off by an amount within its capacity to be adjusted,
would you adjust it or not?

In article <[email hidden]>,

Diablo Scott said:

Benjamin Lewis said:

I get significantly better precision in my rollout measurements than my
cycle computer allows (I can only enter rim circumference to the nearest
centimeter, but can accurately measure to within a mm or so). I could, of
course, use this additional measurement precision to obtain a corrective
factor for my computer's readout, but readings within the +/- 0.25% accuracy
given by the 1 cm calibration limit are already good enough for my
purposes.

OK, if you were to ride a course of a mile or so that you were certain
had been precisely measured, and you found your computer's distance
function to be off by an amount within its capacity to be adjusted,
would you adjust it or not?

No. My roll out measurement is accurate to the precision
of the cyclocomputer. As calculated in another article in
this thread,

<[email hidden]>

the difference in arc length between a straight line and
the track described by a bicycle wheel as ridden by a
typical rider going straight is negligible. Nevertheless,
if the difference were something to consider, I would
still use my roll out measurement. I want to measure the
distance the the wheel rolls, not the map distance.

--
Michael Press

On Tue, 17 Jan 2006 00:32:09 GMT, "Mike Jacoubowsky"
<[email hidden]> wrote:

[---]

Quoted message said:

Anyway, like I said, it's simply "fun" to have a spon-on accurate bike
computer.

What's the effect of varying tyre pressure on its accuracy?

Quoted message said:

Quoted message said:

Anyway, like I said, it's simply "fun" to have a spon-on accurate bike
computer.

What's the effect of varying tyre pressure on its accuracy?

Within the narrow range of pressure that I ride, not much at all. But I
wonder what happens with a 38c hybrid customer, where you might get a range
between 35 & 90psi? But my guess is that the degree to which it matters to
that customer is in direct relation to the degree to which they're fanatical
about tire pressure.

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA

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

Quoted message said:

On Tue, 17 Jan 2006 00:32:09 GMT, "Mike Jacoubowsky"
<[email hidden]> wrote:

[---]

Quoted message said:

Anyway, like I said, it's simply "fun" to have a spon-on accurate bike
computer.

What's the effect of varying tyre pressure on its accuracy?

In article <[email hidden]>,

Andrew Price said:

On Tue, 17 Jan 2006 00:32:09 GMT, "Mike Jacoubowsky"
<[email hidden]> wrote:

[---]

Quoted message said:

Anyway, like I said, it's simply "fun" to have a spon-on accurate bike
computer.

What's the effect of varying tyre pressure on its accuracy?

A 622x25 tire is about 780 mm in diameter. The roll out
decreases by ~ 3 mm for each millimeter the tire deforms
at the contact patch. We can estimate the contact patch
size and estimate the deformation under load also, but,
hey, let's measure it.

Rider and bicycle mass: 80 kg
Wheel circumference: 2125 mm
Roll out, 120 psi: 2107 mm
Roll out, 90 psi: 2099 mm

A fractional difference of ~ 0.004 between 90 psi and 120.

--
Michael Press

Diablo Scott said:

Benjamin Lewis said:

I get significantly better precision in my rollout measurements than my
cycle computer allows (I can only enter rim circumference to the nearest
centimeter, but can accurately measure to within a mm or so). I could,
of course, use this additional measurement precision to obtain a
corrective factor for my computer's readout, but readings within the +/-
0.25% accuracy given by the 1 cm calibration limit are already good
enough for my purposes.

OK, if you were to ride a course of a mile or so that you were certain
had been precisely measured, and you found your computer's distance
function to be off by an amount within its capacity to be adjusted, would
you adjust it or not?

That depends. If that occurred outside of the precision of my computer, I
would have to figure out how to change my model to account for the
difference before I could answer your question. I don't know what I'd do
if I *couldn't* find a way to account for the difference, but fortunately
this has not occurred, because my computer is indeed accurate.

--
Benjamin Lewis

Now is the time for all good men to come to.
-- Walt Kelly

Mike Jacoubowsky said:

Quoted message said:

Quoted message said:

Anyway, like I said, it's simply "fun" to have a spon-on accurate bike
computer.

What's the effect of varying tyre pressure on its accuracy?

Within the narrow range of pressure that I ride, not much at all. But I
wonder what happens with a 38c hybrid customer, where you might get a
range between 35 & 90psi? But my guess is that the degree to which it
matters to that customer is in direct relation to the degree to which
they're fanatical about tire pressure.

Anyone interested in determining the answer could plot the results for ten
different tire pressures during ten commercial breaks. How many breaks are
there in the average TV hour? 🙂

--
Benjamin Lewis

Now is the time for all good men to come to.
-- Walt Kelly

In article
<[email hidden]>,

Michael Press said:

In article <[email hidden]>,

Andrew Price said:

On Tue, 17 Jan 2006 00:32:09 GMT, "Mike Jacoubowsky"
<[email hidden]> wrote:

[---]

Quoted message said:

Anyway, like I said, it's simply "fun" to have a spon-on accurate bike
computer.

What's the effect of varying tyre pressure on its accuracy?

A 622x25 tire is about 780 mm in diameter. The roll out
decreases by ~ 3 mm for each millimeter the tire deforms
at the contact patch. We can estimate the contact patch
size and estimate the deformation under load also, but,
hey, let's measure it.

Rider and bicycle mass: 80 kg
Wheel circumference: 2125 mm

^^^^
Correction: 2127 mm

Quoted message said:

Roll out, 120 psi: 2107 mm
Roll out, 90 psi: 2099 mm

A fractional difference of ~ 0.004 between 90 psi and 120.

--
Michael Press

Sandy said:

Not being overly interested in the expense of one of these GPS thingies, I
can't figure out what they do, if not give you mileage and position. Why
would you care what a separate bike computer says, if you trust in the GPS.
Don't they offer the same info as a bike computer ?

GPS isn't so hot at accurate speed, especially speed profile over time
etc. GPS is for position and not getting lost, not for mileage and speed.

Jasper