Wheelspin

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

Quoted message said:

Hi All,

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

Was your ride dead straight, including the normal miniscule weave due to
balancing?

cheers,
clive

Did you get off periodically to check that they weren't about to go out
of sync by a full revolution?

Clive George said:

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

Quoted message said:

Hi All,

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

Was your ride dead straight, including the normal miniscule weave due to
balancing?

Yes, nothing that would be considered "cornering".

Joseph

tiborg said:

Did you get off periodically to check that they weren't about to go out
of sync by a full revolution?

Nope.

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

Quoted message said:

Clive George said:

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

Quoted message said:

Hi All,

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

Was your ride dead straight, including the normal miniscule weave due to
balancing?

Yes, nothing that would be considered "cornering".

So you started in one place and ended up 60km away in a straight line? On
rolling hills? Were the romans anywhere near your road?
What about the normal weave due to balancing?

cheers,
clive

Quoted message said:

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

Same tire "roll out" front and rear with you on the bike? If you have
the same tires and same pressure front and rear, I'd expect a smaller
effective diameter on the rear wheel because of more weight on it
(therefore, more revolutions than the front).

As someone else mentioned, it would be necessary to check the valve
positions periodically to be sure that the relative positions didn't
change by more than a full 360 degrees. I'm guessing that would be the
case over 60 km.

An interesting puzzle though.

Art Harris

Quoted message said:

Clive George said:

<[email hidden]> wrote i

Quoted message said:

Hi All,

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

Was your ride dead straight, including the normal miniscule weave due to
balancing?

Yes, nothing that would be considered "cornering".

It's simply not possible for a bicycle to ride "dead straight", as
balancing the thing requires continuous corrections of the front wheel
to keep the center of mass over the contact patches.

For /all/ riders, the track of the front wheel is a sinusoidal repeating
curve which is always longer than the path of the rear wheel. It's easy
to observe this in the tracks of a bike's wheels in dirt or snow.

Another proof is to attempt to ride a bicycle with the headset adjusted
very tight, or welded, so that it cannot turn. The rider can go only a
few feet before toppling over hilariously.

--
Ted Bennett

Quoted message said:

Hi All,

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

My "guess" is that you can't tell, because the difference would be
greater than one revolution. But the rear will rotate a bit faster.

Differences in tire pressure and load change the effective
circumference (rollout) of the tire even when coasting. So your two
tires, with different loads, would not be expected to rotate exactly in
synch. That's even more true given that the rear tire is doing the
pushing, and would display some creep.

A related issue: My wife and I have different brands of cyclometers on
our bikes. I always calibrate them by rollout measurements at proper
tire pressure with proper weight on the bikes. Somehow, hers
invariably comes out measuring less mileage than mine, by a percent or
two. I have to fiddle with her calibration so she doesn't feel like
she was cheated!

- Frank Krygowski

Quoted message said:

Hi All,

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

Joseph

Dear Joseph,

Unpredictable would be my guess.

Photograph the front and rear wheel valve stems on one side of a car.

Drive it a few miles down the shoulder of a straight highway.

Stop and photograph the valve stems again.

Their relationship will almost certainly have changed.

Given identical tires and inflation, the effective diameter (roll-out)
of the more heavily loaded tire is slightly smaller.

Cheers,

Carl Fogel

Ted Bennett said:

Quoted message said:

Clive George said:

<[email hidden]> wrote i
> Hi All,
>
> Just for laughs today on my 60km ride, I started out with the valve
> stems in sync. This was a casual ride on rolling fills with fixed gear.
> No front braking, and only about 4 short downhill "slowings" with the
> rear. No discernible wheelslip. Any guesses as to what the difference
> was at the end of the ride?

Was your ride dead straight, including the normal miniscule weave due to
balancing?

Yes, nothing that would be considered "cornering".

It's simply not possible for a bicycle to ride "dead straight", as
balancing the thing requires continuous corrections of the front wheel
to keep the center of mass over the contact patches.

The road was a 20km loop that meanders in and out of glacial rock
formations. No Romans involved. So it was not "dead" straight. I only
meant that there was no turns involved where one would expect tire
scrub.

Quoted message said:

For /all/ riders, the track of the front wheel is a sinusoidal repeating
curve which is always longer than the path of the rear wheel. It's easy
to observe this in the tracks of a bike's wheels in dirt or snow.

As a matter of fact there was a light frost so I could see my tracks
(and those of others) on subsequent loops. Mine were the ones that
looked like a unicycle made them ;-). For fun I try to ride as straight
as I can, so usually the front wheel curve is within the total width of
the back track so it just looks like one line in the frost.

Quoted message said:

Another proof is to attempt to ride a bicycle with the headset adjusted
very tight, or welded, so that it cannot turn. The rider can go only a
few feet before toppling over hilariously.

Ah yes, the dreaded "indexed steering" that is a feature of some of my
bikes!

Joseph

Art Harris said:

Quoted message said:

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

Same tire "roll out" front and rear with you on the bike? If you have
the same tires and same pressure front and rear, I'd expect a smaller
effective diameter on the rear wheel because of more weight on it
(therefore, more revolutions than the front).

Same tires, different pressures. More in the back. My weight balance is
significantly rearward I think, so I'm sure there is a smaller rear
diameter despite the differing pressures.

Joseph

Quoted message said:

As someone else mentioned, it would be necessary to check the valve
positions periodically to be sure that the relative positions didn't
change by more than a full 360 degrees. I'm guessing that would be the
case over 60 km.

An interesting puzzle though.

Art Harris

Quoted message said:

Quoted message said:

Hi All,

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

Joseph

Dear Joseph,

Unpredictable would be my guess.

The answer is "no change". Exactly the same as when I left. I wonder
how many times it went 360 deg? I wonder how much was slip and how much
was diameter difference? I suppose I could test by using 2 identical
cycle computers calibrated by weighted roll-out, one on the front, one
on the back. If the rear measures more distance it slipped.

Joseph

Ted Bennett said:

Quoted message said:

Clive George said:

<[email hidden]> wrote i

>Hi All,
>
>Just for laughs today on my 60km ride, I started out with the valve
>stems in sync. This was a casual ride on rolling fills with fixed gear.
>No front braking, and only about 4 short downhill "slowings" with the
>rear. No discernible wheelslip. Any guesses as to what the difference
>was at the end of the ride?

Was your ride dead straight, including the normal miniscule weave due to
balancing?

Yes, nothing that would be considered "cornering".

It's simply not possible for a bicycle to ride "dead straight", as
balancing the thing requires continuous corrections of the front wheel
to keep the center of mass over the contact patches.

For /all/ riders, the track of the front wheel is a sinusoidal repeating
curve which is always longer than the path of the rear wheel. It's easy
to observe this in the tracks of a bike's wheels in dirt or snow.

Another proof is to attempt to ride a bicycle with the headset adjusted
very tight, or welded, so that it cannot turn. The rider can go only a
few feet before toppling over hilariously.

Really?! <pops out to bike shed with welding torch>

Quoted message said:

Quoted message said:

Hi All,

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

Joseph

Dear Joseph,

Unpredictable would be my guess.

Photograph the front and rear wheel valve stems on one side of a car.

Drive it a few miles down the shoulder of a straight highway.

Stop and photograph the valve stems again.

Their relationship will almost certainly have changed.

Given identical tires and inflation, the effective diameter (roll-out)
of the more heavily loaded tire is slightly smaller.

Cheers,

Carl Fogel

The rear may rotate faster due to more load and resulting reduced
effective wheel diameter but if there is any turning at all, the front
travels farther being on a larger radius with the rear tracking inside
on a shorter radius. Just balancing steers the front back and forth
while the rear travels a straighter line.

To keep the wheels in sync, ride perfectly straight until the rear is
ahead, then wobble back and forth until the front catches up. Stop every
km to check.

Dan said:

To keep the wheels in sync, ride perfectly straight until the rear is
ahead, then wobble back and forth until the front catches up. Stop every
km to check.

Sounds like a plan. I'll report back with results tomorrow.

"But Honey, of course I have to take another long ride today too. It's
for science, and lots of people are counting on me!"

Joseph

Let's assume that the two wheels are identical in size.
Assume the path of the front wheel is a sinusoid with
wavelength Lw and amplitude A. We can approximate
the distance traveled by the wheel as

(1) L = Lw*(1 + (pi*A/Lw)^2).

From Bicycling Science, 3rd edition, p. 269, the
amplitude of the rear wheel is

(2) B = A/sqrt(q + (2*pi*Lb/Lw)^2).

N.B. My Lw is D in the book, and my Lb is Lw in the book.

From these we can compute the difference in travel
between front and rear wheels for a given straight distance,
set this equal to the wheel circumference, and solve for
the total distance. I get

(3) Lt = Dw*Lw^2*(Lw^2 + 4*pi^2*Lb^2)/4/pi^3/A^2/Lb^2

Assume that

Dw = wheel diameter = 27 inch
Lb = wheel base = 36 inch
A = amplitude of wobble = 2 inch
Lw = wavelength of wobble (guess) = 240 inch

then the distance required for the front wheel to
turn one more revolution than the rear is about
4 miles. Note, however, that this is a fourth-power
of Lw (wavelength of wobble) so your mileage may vary.

--
Joe Riel

Joe Riel said:

(2) B = A/sqrt(q + (2*pi*Lb/Lw)^2).

typo. q should be 1.

(2) B = A/sqrt(1 + (2*pi*Lb/Lw)^2).

--
Joe Riel

Joe Riel said:

Let's assume that the two wheels are identical in size.
Assume the path of the front wheel is a sinusoid with
wavelength Lw and amplitude A. We can approximate
the distance traveled by the wheel as

(1) L = Lw*(1 + (pi*A/Lw)^2).

From Bicycling Science, 3rd edition, p. 269, the
amplitude of the rear wheel is

(2) B = A/sqrt(q + (2*pi*Lb/Lw)^2).

N.B. My Lw is D in the book, and my Lb is Lw in the book.

From these we can compute the difference in travel
between front and rear wheels for a given straight distance,
set this equal to the wheel circumference, and solve for
the total distance. I get

(3) Lt = Dw*Lw^2*(Lw^2 + 4*pi^2*Lb^2)/4/pi^3/A^2/Lb^2

Assume that

Dw = wheel diameter = 27 inch
Lb = wheel base = 36 inch
A = amplitude of wobble = 2 inch
Lw = wavelength of wobble (guess) = 240 inch

then the distance required for the front wheel to
turn one more revolution than the rear is about
4 miles. Note, however, that this is a fourth-power
of Lw (wavelength of wobble) so your mileage may vary.

That is very interesting. I wonder if this can be quantified in terms
of "wasted" effort. In other words, how much time can one (if at all)
save by minimizing amplitude and wavelength of wobble. I'm thinking
more in terms of resistance from scrub or other factors rather than
increased distance covered (unless the object is RAAM...).

Joseph

Quoted message said:

Hi All,

Just for laughs today on my 60km ride, I started out with the valve
stems in sync. This was a casual ride on rolling fills with fixed gear.
No front braking, and only about 4 short downhill "slowings" with the
rear. No discernible wheelslip. Any guesses as to what the difference
was at the end of the ride?

Joseph

Random. If they are at all near each other it's because the front has
lapped the rear - or more. As Sherlock Holmes noted, the front path
describes a wider radius. Repeatedly. The constant series of corrections
means the valve positions end up randomly aligned.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971