Calibrating a cyclocomputer

[Chad Waldman]

I just bought my first computer (Ascent Delta V) and I am confused on
how to calibrate it for my tires. I am riding a mtn bike with slick
tires (26 x 1.25).

The chart in the instructions does not include this tire size. I have
read other web sites to figure out what to enter in my computer (which
appears to take circumference in mm) however the numbers given on my
chart (and my friend's, who has a Bell) differs from the numbers given
on web sites and my other friend's computer (which is a Cateye). All
appear to use circumference in mm.

Example: Take the 26 x 1.5 tire size. I have listed on my chart: ATB 26
x 1.5 = 2030.
On http://www.sheldonbrown.com/cyclecomputer_calibration.html, it lists
for a 26 x 1.5, 1985. Why are they so far off? This concerns me.
Sheldon's site's chart also seems inaccurate. For example, for the 26 x
1.5 size tire, Group A (which is listed as circumference in inches)
lists 77.71in and for Group F (circumference in mm) lists 1985mm. Last
time I checked however, 77.71in = 1974 mm. Why the discrepancy?

After measuring and trying the rolling test to the best of my ability, I
got roughly 1975mm. On Sheldon's site for a 26 x 1.25 size tire, he
lists 77.44 in = 1967mm, or he lists (in Group F) 1953mm.

What should I enter? How much do these numbers make a difference in the
great scheme of things? I usually ride between 30 and 50 miles at a
time. How much could I possibly expect to be off if I am off by say
20mm?

Thanks,
Chad

 

[Leo Lichtman]

"Chad Waldman" wrote: (clip) I usually ride between 30 and 50 miles at a
time How much could I possibly expect to be off if I am off by say 20mm?
^^^^^^^^^^^^^^^^^^^
20 mm in 2000 is 1%, which is a half mile in 50 miles. That may seem like a
lot, but it's only about 50 ft per mile. Do you have a reason to need miore
accuracy than that?

 

[Sheldon Brown]

Chad Waldman wrote:
> I just bought my first computer (Ascent Delta V) and I am confused on
> how to calibrate it for my tires. I am riding a mtn bike with slick
> tires (26 x 1.25).
>
> The chart in the instructions does not include this tire size. I have
> read other web sites to figure out what to enter in my computer (which
> appears to take circumference in mm) however the numbers given on my
> chart (and my friend's, who has a Bell) differs from the numbers given
> on web sites and my other friend's computer (which is a Cateye). All
> appear to use circumference in mm.
>
> Example: Take the 26 x 1.5 tire size. I have listed on my chart: ATB 26
> x 1.5 = 2030.
> On http://www.sheldonbrown.com/cyclecomputer_calibration.html, it lists
> for a 26 x 1.5, 1985. Why are they so far off? This concerns me.
> Sheldon's site's chart also seems inaccurate. For example, for the 26 x
> 1.5 size tire, Group A (which is listed as circumference in inches)
> lists 77.71in and for Group F (circumference in mm) lists 1985mm. Last
> time I checked however, 77.71in = 1974 mm. Why the discrepancy?

If you would have looked immediately below the chart, you would have seen:

"Inconsistencies

"The calibration charts are to a large extent based on instruction
sheets provided with various cyclecomputers. Different manufacturers
would have used different brands of tires to calibrate, so there are
some areas where there is slight inconsistancy in values between one
group and another.
"If you requre greater accuracy than this chart provides, do a rollout
test or measured distance test."

The inch circumference values are used by Avocet cyclometers, and are
teh numbers provided by Avocet. My guess is that they used Avocet tires
to derive the values. Back in the day, Avocet made only slick tires,
with no knobs to inflate the numbers, and they also tended to run
narrower than marked.

Sheldon "The One Percent Solution" Brown
+------------------------------------+
| A good plan today is better than |
| a perfect plan tomorrow. |
| --David Mamet |
| (Wag the Dog, Bulworth) |
+------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

 

[Q]

I use a GPS to fine tune my calibration.

Q

 

[[email protected]]

I suggest trusting your rollout measurement rather than the
manufacturer guesstimate. To validate your rollout, measure the
diameter of your tire (outside tread to outside tread) in mm and
multiply by Pi (3.14159). This should be very close to your rollout
measurement. Probably won't be exact to the mm. You could use the
average of the two.

 

[Hank Wirtz]

I live right on a state highway, and there's a mile marker on the corner.
When I want to calibrate, I ride from that mile marker to the next, then
adjust by whatever % I'm off. Works pretty well.

 

[Mike Reed]

[email protected] wrote:
> I suggest trusting your rollout measurement rather than the
> manufacturer guesstimate. To validate your rollout, measure the
> diameter of your tire (outside tread to outside tread) in mm and
> multiply by Pi (3.14159). This should be very close to your rollout
> measurement. Probably won't be exact to the mm. You could use the
> average of the two.

I would think the two measurements would differ significantly since the
tire is unweighted when measuring the diameter. I think it's still a
valid check to see that the rolling measurement is always less than the
diameter-measured circumference.

-Mike

 

[Michael Press]

In article
<[email protected]>,
[email protected] wrote:

> I suggest trusting your rollout measurement rather than the
> manufacturer guesstimate. To validate your rollout, measure the
> diameter of your tire (outside tread to outside tread) in mm and
> multiply by Pi (3.14159). This should be very close to your rollout
> measurement. Probably won't be exact to the mm. You could use the
> average of the two.

* Put a piece of masking tape on the front tire
transverse to the direction of travel.

* Put a piece of masking tape on the floor transverse to
the direction of travel.

* Match the two pieces of tape, the front of the tape on
the wheel at the center of the contact patch and justified
with the front of the piece of tape on the floor.

* Mount the bicycle and roll forward until the tape on
the wheel is again at the center of the contact patch, and
lock the front brake.

* Dismount and place a piece of tape on the floor
justified with the tape on the tire.

* Measure the distance between the pieces of tape on the
floor. This is your wheel roll out distance.

Do not average this number with any other number. This the
best you can do.

An assistant will aid tremendously in this measurement.

--
Michael Press

 

[Lou Holtman]

Michael Press wrote:
> In article
> <[email protected]>,
> [email protected] wrote:
>
>
>>I suggest trusting your rollout measurement rather than the
>>manufacturer guesstimate. To validate your rollout, measure the
>>diameter of your tire (outside tread to outside tread) in mm and
>>multiply by Pi (3.14159). This should be very close to your rollout
>>measurement. Probably won't be exact to the mm. You could use the
>>average of the two.
>
>
> * Put a piece of masking tape on the front tire
> transverse to the direction of travel.
>
> * Put a piece of masking tape on the floor transverse to
> the direction of travel.
>
> * Match the two pieces of tape, the front of the tape on
> the wheel at the center of the contact patch and justified
> with the front of the piece of tape on the floor.
>
> * Mount the bicycle and roll forward until the tape on
> the wheel is again at the center of the contact patch, and
> lock the front brake.
>
> * Dismount and place a piece of tape on the floor
> justified with the tape on the tire.
>
> * Measure the distance between the pieces of tape on the
> floor. This is your wheel roll out distance.
>
> Do not average this number with any other number. This the
> best you can do.
>
> An assistant will aid tremendously in this measurement.
>


It is not necessary to mount the bicycle. Just walk along the bike and
apply about the same pressure on the bar/hoods as you would on the bike.
That's accurate enough. No need to do acrobatics in the garage/driveway

Lou
--
Posted by news://news.nb.nu

 

[[email protected]]

anonymous writes:

> I suggest trusting your rollout measurement rather than the
> manufacturer guesstimate. To validate your rollout, measure the
> diameter of your tire (outside tread to outside tread) in mm and
> multiply by Pi (3.14159). This should be very close to your rollout
> measurement. Probably won't be exact to the mm. You could use the
> average of the two.

You can prove to yourself how wrong that it by measuring the rollout
distance by walking the bicycle through one revolution and doing it
again when seated on the bicycle in normal riding position. There is
a difference and it is the amount that people quibble about endlessly.

Sit on the bicycle next to a wall so you can start and stop accurately
and measure the distance with a Stanley (Powerlock) steel tape. Sight
down the axle to see when the valve stem is directly over the tire
contact center starting at a floor tile edge or crack in the sidewalk.

Jobst Brandt

 

[[email protected]]

Lou Holtman writes:

>>> I suggest trusting your rollout measurement rather than the
>>> manufacturer guesstimate. To validate your rollout, measure the
>>> diameter of your tire (outside tread to outside tread) in mm and
>>> multiply by Pi (3.14159). This should be very close to your
>>> rollout measurement. Probably won't be exact to the mm. You could
>>> use the average of the two.

>> * Put a piece of masking tape on the front tire transverse to the
>> direction of travel.

>> * Put a piece of masking tape on the floor transverse to the
>> direction of travel.

>> * Match the two pieces of tape, the front of the tape on the wheel
>> at the center of the contact patch and justified with the front of
>> the piece of tape on the floor.

>> * Mount the bicycle and roll forward until the tape on the wheel is
>> again at the center of the contact patch, and lock the front brake.

>> * Dismount and place a piece of tape on the floor justified with
>> the tape on the tire.

>> * Measure the distance between the pieces of tape on the
>> floor. This is your wheel roll out distance.

>> Do not average this number with any other number. This the best you
>> can do.

>> An assistant will aid tremendously in this measurement.

> It is not necessary to mount the bicycle. Just walk along the bike
> and apply about the same pressure on the bar/hoods as you would on
> the bike. That's accurate enough. No need to do acrobatics in the
> garage/driveway

How to you say that with such certainty? I'm sure you haven't tried
it but your assertion is wrong. Load on the tire makes a difference.
Your weight on the saddle loads the front wheel in addition to the
hands on the bars. Try it.

Jobst Brandt

 

[Lou Holtman]

[email protected] wrote:
> Lou Holtman writes:
>
>
>>>>I suggest trusting your rollout measurement rather than the
>>>>manufacturer guesstimate. To validate your rollout, measure the
>>>>diameter of your tire (outside tread to outside tread) in mm and
>>>>multiply by Pi (3.14159). This should be very close to your
>>>>rollout measurement. Probably won't be exact to the mm. You could
>>>>use the average of the two.
>
>
>>>* Put a piece of masking tape on the front tire transverse to the
>>>direction of travel.
>
>
>>>* Put a piece of masking tape on the floor transverse to the
>>>direction of travel.
>
>
>>>* Match the two pieces of tape, the front of the tape on the wheel
>>>at the center of the contact patch and justified with the front of
>>>the piece of tape on the floor.
>
>
>>>* Mount the bicycle and roll forward until the tape on the wheel is
>>>again at the center of the contact patch, and lock the front brake.
>
>
>>>* Dismount and place a piece of tape on the floor justified with
>>>the tape on the tire.
>
>
>>>* Measure the distance between the pieces of tape on the
>>>floor. This is your wheel roll out distance.
>
>
>>>Do not average this number with any other number. This the best you
>>>can do.
>
>
>>>An assistant will aid tremendously in this measurement.
>
>
>>It is not necessary to mount the bicycle. Just walk along the bike
>>and apply about the same pressure on the bar/hoods as you would on
>>the bike. That's accurate enough. No need to do acrobatics in the
>>garage/driveway
>
>
> How to you say that with such certainty? I'm sure you haven't tried
> it but your assertion is wrong. Load on the tire makes a difference.
> Your weight on the saddle loads the front wheel in addition to the
> hands on the bars. Try it.
>
> Jobst Brandt


The question is what is good enough? I think within 0.5-1% is good
enough for me and I'm sure I get that result with this method. Yes I
tried sitting on the bike once and almost broke my neck ;-) Once I even
measured what the influence was of the tire pressure. I rode the same
course (27.6 km) once with the front tire inflated to 4 bar (cornering
was really scary) and the second time inflated to 8 bar. The measured
distance was exactly the same: 27.6 km (I still have the logging of that
test somewhere). From that moment I'm convinced that mounting the bike
is not necessary to get a result within 1% accuracy. YMMV though.

Lou
--
Posted by news://news.nb.nu

 

[Michael Press]

In article <[email protected]>,
Lou Holtman <[email protected]> wrote:

> Michael Press wrote:
> > In article
> > <[email protected]>,
> > [email protected] wrote:
> >
> >
> >>I suggest trusting your rollout measurement rather than the
> >>manufacturer guesstimate. To validate your rollout, measure the
> >>diameter of your tire (outside tread to outside tread) in mm and
> >>multiply by Pi (3.14159). This should be very close to your rollout
> >>measurement. Probably won't be exact to the mm. You could use the
> >>average of the two.
> >
> >
> > * Put a piece of masking tape on the front tire
> > transverse to the direction of travel.
> >
> > * Put a piece of masking tape on the floor transverse to
> > the direction of travel.
> >
> > * Match the two pieces of tape, the front of the tape on
> > the wheel at the center of the contact patch and justified
> > with the front of the piece of tape on the floor.
> >
> > * Mount the bicycle and roll forward until the tape on
> > the wheel is again at the center of the contact patch, and
> > lock the front brake.
> >
> > * Dismount and place a piece of tape on the floor
> > justified with the tape on the tire.
> >
> > * Measure the distance between the pieces of tape on the
> > floor. This is your wheel roll out distance.
> >
> > Do not average this number with any other number. This the
> > best you can do.
> >
> > An assistant will aid tremendously in this measurement.
> >
>
>
> It is not necessary to mount the bicycle. Just walk along the bike and
> apply about the same pressure on the bar/hoods as you would on the bike.
> That's accurate enough. No need to do acrobatics in the garage/driveway

I measured this. Did you?

A 622x25 tire is about 780 mm in diameter.

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

The relative change in roll out when the bicycle is loaded
from the unloaded state is about 25 parts in 2000, or
0.02.

--
Michael Press

 

[Michael Press]

In article <[email protected]>,
Lou Holtman <[email protected]> wrote:

> [email protected] wrote:
> > Lou Holtman writes:
> >
> >
> >>>>I suggest trusting your rollout measurement rather than the
> >>>>manufacturer guesstimate. To validate your rollout, measure the
> >>>>diameter of your tire (outside tread to outside tread) in mm and
> >>>>multiply by Pi (3.14159). This should be very close to your
> >>>>rollout measurement. Probably won't be exact to the mm. You could
> >>>>use the average of the two.
> >
> >
> >>>* Put a piece of masking tape on the front tire transverse to the
> >>>direction of travel.
> >
> >
> >>>* Put a piece of masking tape on the floor transverse to the
> >>>direction of travel.
> >
> >
> >>>* Match the two pieces of tape, the front of the tape on the wheel
> >>>at the center of the contact patch and justified with the front of
> >>>the piece of tape on the floor.
> >
> >
> >>>* Mount the bicycle and roll forward until the tape on the wheel is
> >>>again at the center of the contact patch, and lock the front brake.
> >
> >
> >>>* Dismount and place a piece of tape on the floor justified with
> >>>the tape on the tire.
> >
> >
> >>>* Measure the distance between the pieces of tape on the
> >>>floor. This is your wheel roll out distance.
> >
> >
> >>>Do not average this number with any other number. This the best you
> >>>can do.
> >
> >
> >>>An assistant will aid tremendously in this measurement.
> >
> >
> >>It is not necessary to mount the bicycle. Just walk along the bike
> >>and apply about the same pressure on the bar/hoods as you would on
> >>the bike. That's accurate enough. No need to do acrobatics in the
> >>garage/driveway
> >
> >
> > How to you say that with such certainty? I'm sure you haven't tried
> > it but your assertion is wrong. Load on the tire makes a difference.
> > Your weight on the saddle loads the front wheel in addition to the
> > hands on the bars. Try it.
> >
> > Jobst Brandt
>
>
> The question is what is good enough? I think within 0.5-1% is good
> enough for me

How about 2% ? That is the the relative difference that I measured.

> and I'm sure I get that result with this method. Yes I
> tried sitting on the bike once and almost broke my neck ;-)

So sad.

> Once I even
> measured what the influence was of the tire pressure. I rode the same
> course (27.6 km) once with the front tire inflated to 4 bar (cornering
> was really scary) and the second time inflated to 8 bar. The measured
> distance was exactly the same: 27.6 km (I still have the logging of that
> test somewhere). From that moment I'm convinced that mounting the bike
> is not necessary to get a result within 1% accuracy. YMMV though.

--
Michael Press

 

[Leo Lichtman]

"Michael Press" wrote: (clip) The relative change in roll out when the
bicycle is loaded from the unloaded state is about 25 parts in 2000, or
0.02.
^^^^^^^^^^^^
Um...it's closer to .01, Michael.

 

[Michael Press]

In article
<[email protected]>,
"Leo Lichtman" <[email protected]> wrote:

> "Michael Press" wrote: (clip) The relative change in roll out when the
> bicycle is loaded from the unloaded state is about 25 parts in 2000, or
> 0.02.
> ^^^^^^^^^^^^
> Um...it's closer to .01, Michael.

Drat! So it is.

--
Michael Press

 

[[email protected]]

Lou Holtman writes:

>>>>> I suggest trusting your rollout measurement rather than the
>>>>> manufacturer guesstimate. To validate your rollout, measure the
>>>>> diameter of your tire (outside tread to outside tread) in mm and
>>>>> multiply by Pi (3.14159). This should be very close to your
>>>>> rollout measurement. Probably won't be exact to the mm. You
>>>>> could use the average of the two.

>>>> * Put a piece of masking tape on the front tire transverse to the
>>>> direction of travel.

>>>> * Put a piece of masking tape on the floor transverse to the
>>>> direction of travel.

>>>> * Match the two pieces of tape, the front of the tape on the
>>>> wheel at the center of the contact patch and justified with the
>>>> front of the piece of tape on the floor.

>>>> * Mount the bicycle and roll forward until the tape on the wheel
>>>> is again at the center of the contact patch, and lock the front
>>>> brake.

>>>> * Dismount and place a piece of tape on the floor justified with
>>>> the tape on the tire.

>>>> * Measure the distance between the pieces of tape on the
>>>> floor. This is your wheel roll out distance.

>>>> Do not average this number with any other number. This the best
>>>> you can do.

>>>> An assistant will aid tremendously in this measurement.

>>> It is not necessary to mount the bicycle. Just walk along the
>>> bike and apply about the same pressure on the bar/hoods as you
>>> would on the bike. That's accurate enough. No need to do
>>> acrobatics in the garage/driveway

>> How to you say that with such certainty? I'm sure you haven't tried
>> it but your assertion is wrong. Load on the tire makes a difference.
>> Your weight on the saddle loads the front wheel in addition to the
>> hands on the bars. Try it.

> The question is what is good enough? I think within 0.5-1% is good
> enough for me and I'm sure I get that result with this method. Yes
> I tried sitting on the bike once and almost broke my neck ;-) Once I
> even measured what the influence was of the tire pressure. I rode
> the same course (27.6 km) once with the front tire inflated to 4 bar
> (cornering was really scary) and the second time inflated to 8 bar.
> The measured distance was exactly the same: 27.6 km (I still have
> the logging of that test somewhere). From that moment I'm convinced
> that mounting the bike is not necessary to get a result within 1%
> accuracy. YMMV though.

Well, that's a nice dodge but if "good enough" is your choice, then
just use the number in the user's manual and be done with it. Your
mileage WILL vary and advising others to do likewise is presumptuous.

Jobst Brandt

 

[Lou Holtman]

<[email protected]> wrote in message
news:[email protected]...
> Lou Holtman writes:
>>
> > The question is what is good enough? I think within 0.5-1% is good
> > enough for me and I'm sure I get that result with this method. Yes
> > I tried sitting on the bike once and almost broke my neck ;-) Once I
> > even measured what the influence was of the tire pressure. I rode
> > the same course (27.6 km) once with the front tire inflated to 4 bar
> > (cornering was really scary) and the second time inflated to 8 bar.
> > The measured distance was exactly the same: 27.6 km (I still have
> > the logging of that test somewhere). From that moment I'm convinced
> > that mounting the bike is not necessary to get a result within 1%
> > accuracy. YMMV though.
>
> Well, that's a nice dodge but if "good enough" is your choice, then
> just use the number in the user's manual and be done with it. Your
> mileage WILL vary and advising others to do likewise is presumptuous.


Dodge? Presumptuous? Jobst, I'm not arguing that the roll out measement
sitting on the bike, the tires inflated to the proper pressure and pushed
around by an assistent gives the best possible result. I'm just give an
alternative when you have to do it by your own and find balancing the bike
in your garage is to much of a hassle. I did some measurements and
experiments and came to the conclusion that by just applying some force on
the handlebar instead of sitting on the bike gives you a result within 1%
accuracy; problably better. The measurements Michel Press presented show
that too. Let the readers decide.
Jobst how do you know at what accuracy you have calibrated your computer?
Does sitting on the saddle all the time or riding out of the saddle a lot
has a significant influence?
Why o why did I measure the same distance at 4 bar and 8 bar?

Lou

 

[[email protected]]

Chad Waldman wrote:
> I just bought my first computer (Ascent Delta V) and I am confused on
> how to calibrate it for my tires. I am riding a mtn bike with slick
> tires (26 x 1.25).
>
> The chart in the instructions does not include this tire size. I have
> read other web sites to figure out what to enter in my computer (which
> appears to take circumference in mm) however the numbers given on my
> chart (and my friend's, who has a Bell) differs from the numbers given
> on web sites and my other friend's computer (which is a Cateye). All
> appear to use circumference in mm.
>
> Example: Take the 26 x 1.5 tire size. I have listed on my chart: ATB 26
> x 1.5 = 2030.
> On http://www.sheldonbrown.com/cyclecomputer_calibration.html, it lists
> for a 26 x 1.5, 1985. Why are they so far off? This concerns me.
> Sheldon's site's chart also seems inaccurate. For example, for the 26 x
> 1.5 size tire, Group A (which is listed as circumference in inches)
> lists 77.71in and for Group F (circumference in mm) lists 1985mm. Last
> time I checked however, 77.71in = 1974 mm. Why the discrepancy?
>
> After measuring and trying the rolling test to the best of my ability, I
> got roughly 1975mm. On Sheldon's site for a 26 x 1.25 size tire, he
> lists 77.44 in = 1967mm, or he lists (in Group F) 1953mm.
>
> What should I enter? How much do these numbers make a difference in the
> great scheme of things? I usually ride between 30 and 50 miles at a
> time. How much could I possibly expect to be off if I am off by say
> 20mm?
>
> Thanks,
> Chad

A private email complained that RBT was debating the
effects of inflation and load on tire roll-out without much
actual data and asked me to post my data again.

Again?

I was tempted to reply that I never posted any such data,
but . . .

I bored a hole through the middle of a 2x4, banged a
short piece of pipe through it, roped it to the handlebars
of a spare bicycle lurking in my dungeon, found some old
weights, armed myself with a nicely calibrated tire pump,
and played tailor to the front tire with a measuring tape.

The tire was an old 700x25C on a 622 rim, inflated first to
90 and then to 125 psi.

"No load" means the weight of the bicycle with no rider, a
few pounds of 2x4 and rope, and the slight pressure of the
experimenter's hands pushing the bike around.

The 60-lb test load on the handlebars is less than a typical
front-wheel load, but stacking too many weights on a badly
designed rig turns out to be a bad idea.

(It was determined that an ordinary front wheel and tire can
withstand without damage the impact of five 15-lb weights
toppling forward off the handlebars. Watch your toes.)

On a smooth concrete floor, rollout was measured to 1/16th
of an inch (~1.6mm) three times for each value.

The tests averaged to suspiciously round values:

psi load #1 #2 #3 average
--- ------- -- -- -- -------
125 no load 83 & 08-07-06/16ths = 83 & 07/16ths
125 60 lb 82 & 15-15-15/16ths = 82 & 15/16ths
90 no load 83 & 02-04-03/16ths = 83 & 03/16ths
90 60 lb 82 & 09-10-11/16ths = 82 & 10/16ths

There appears to be no pattern of bias in the variation,
which is either a tribute to the experimenter's impartiality
and objectivity, or else evidence of a well-camouflaged
conspiracy whose goals are too terrible to contemplate.

125psi 125psi 90psi 90 psi
roll-out no load 60 lbs no load 60 lbs
---------- ---------- ---------- ----------
16ths 83 & 07/16 82 & 15/16 83 & 03/16 82 & 10/16
decimal 83.4375 82.9375 83.1875 82.6250
mm 2119.3 2106.6 2113.0 2098.7
mm change 0.0 -12.7 -6.3 -20.6

Roll-out shrank a small but measurable amount with increased
load. Adding a modest load of 60 lbs reduced roll-out roughly
13-14mm, about 0.6%.

Lowering tire pressure also reduced roll-out, roughly 6-8mm
for the drop from 125 to 90 psi, about 0.3%.

Cheers,

Carl Fogel

 

[john]

My God! Look who just popped up from Colorado's frozed snow! He's alive
& still devising experiments :-0