Crank Length Selection

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

Quoted message said:

In article <[email hidden]>,

ddog said:

Lou Holtman said:

It's 2.5 mm difference for Gods sake. Two different socks have the
same effect.

Lou

If God's sake does not include leverage, turning limits, and
biomechanical equilibrium, in a narrow minded overly simplistic
viewpoint you may be right. But because there are always limits that
effect different people differently, overly simplistic one liners are
always wrong and can hurt some people if they weigh your comments as
legitimate arguments.

Remaining agnostic on the god aspect, I'll chime in that "it's only a
2.5 mm difference." Now, in my case, with a measured leg-to-crotch
distance of 910 mm, that 2.5 mm difference is about 0.27% overall. That
seems unlikely to be a significant difference. Switching shoes can
easily result in that much difference. Wearing odd socks might provide
the same difference, as Lou points out. A couple of slices of bologna
in your shoe will also accomplish the same thing. Shouldn't be too
hard- this thread has plenty of bologna to go around.

After a few rides, the bologna might make a big difference....

Chas.

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

Quoted message said:

In article <[email hidden]>,

* * Chas said:

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

Quoted message said:

On Sun, 18 Feb 2007 14:36:05 -0500, John Forrest Tomlinson
<[email hidden]> wrote:

>On Sun, 18 Feb 2007 12:00:35 -0700, [email hidden] wrote:
>
>>A 175.0 mm pedal drops 2.5 mm lower than a 172.5 mm pedal, about
>>a tenth of an inch.
>>
>>The difference in length between your right and left leg is
>>probably twice that much (or more):
>>
>>"A majority of people have a measurable leg length difference of
>>1/4" or more."
>>
>
>So what? My leg length doesn't change much so I don't see what
>your point is.
>
>(My functional leg length did change a little over a long period
>of time due to some forms of soft tissue work. That affected my
>bike fit.)

Dear John,

In all likelihood, one of your legs is longer than the other by
1/4" or more, like most people's legs.

That's about twice as much as the difference in distance from your
hip to pedals attached to 175.0 and 172.5 mm cranks.

When walking or running, few of us can tell which of our legs is
shorter. Indeed, most of us don't even know if we're waddling
around on slightly mismatched legs, any more than we notice that
we're up to an inch shorter by the end of the day, due to the
compression of our spinal disks.

(The change in spinal length during the day says something about
how sensitive we really are to the distance from the seat to the
handlebars.)

Anyone sufficiently curious can ask a friend to swap four 175 and
172.5 crank arms randomly on a bike for a dozen rides, left and
right, and report how well he could tell the difference without
looking at the numbers on the cranks.

A more entertaining experiment would involve leaving the crank
unchanged and lying to a self-described sensitive rider, telling
him that his 175.0 mm cranks were being changed to 172.5 mm and
seeing if he detected the imaginary changes.

A lot of RBT posters have mentioned that they didn't notice what
turned out to be mismatched cranks.

Cheers,

Carl Fogel

The human body has an amazing capacity to compensate. It took me less
than 2 weeks to compensate for a 1 1/4" leg length difference pre and
post hip replacement surgery.

Wow, that's a big difference that far eclipses anything we've talked
about here.

Quoted message said:

There have been experiments using prism glasses where the subjects
view everything upside down all of the time. Within a short period of
time their visual perception flips and everything looks normal.

Well, not exactly, but they do adapt and when they take the prisms off
they have to readapt back to normal!

Quoted message said:

Remember the fairy tale about the princess and the pea?

Exactamundo.

The rehab people had me up and walking a little the next day after
surgery. After several days I noticed the length difference and mentioned
it to my doctor. He said don't worry about it, my body would adjust. After
several weeks it became less and less noticeable. I had to get the inseam
on some of my pants let down.

After 4 years of chronic pain with AVN it was great to not have to take
any medication. There was zero pain from day one. I didn't ride much
during that period so I can't tell what crank length differences would
have meant to me.

I should have mentioned the re-adaptation period after the prism
experiment.

One last note that no one has mentioned in this thread, with longer
cranks, your knee comes up higher and I've seen problems mentioned about
that issue.

Beware of bicycle size nazis who have the one and only correct way to set
up a bike.

Chas.

* * Chas said:

One last note that no one has mentioned in this thread, with longer
cranks, your knee comes up higher and I've seen problems mentioned about
that issue.

Wait, are you arguing that long cranks are bad (the comment above
seems to support that) or that long cranks can be noticed due to the
interfence above (which seems to contradict things you said earlier)?
--
JT
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Joel Mayes said:

On 2007-02-18, David L. Johnson <[email hidden]> wrote:

Quoted message said:

Quoted message said:

The last concern is overblown. Very few such conversions have less than
a 45-degree lean angle before the pedal contacts the road, and if you
are leaning over more than that you are on the way down, anyway. Lots
of people experience hitting a pedal and going down in a corner, but
wrongly infer that the pedal strike caused the fall. Usually it's the
other way around.

This also assumes that the corner you are in is perfectly flat, if the
road slopes upwards into the corner your pedal clearance can be
dramatically shortened.

That logic doesn't work, since if you are on a sloped road (negatively
sloped with respect to the corner, of course) you will still slide out
when your angle with the road is more than 45 degrees.

--

David L. Johnson

"What am I on? I'm on my bike, six hours a day, busting my ass. What
are you on?" --Lance Armstrong

John Forrest Tomlinson said:

Quoted message said:

John Forrest Tomlinson said:

On Sun, 18 Feb 2007 11:02:33 -0800, "* * Chas"
<[email hidden]> wrote:

>Look at a ruler. Now hold your thumb and forefinger 2.5mm (1/8"😉 apart and
>compare that gap with the length of your legs and feet combined.

Place your finger into the opening of a vise that is the same width as
your finger. Now tighten the vise 2.5mm. Do you notice anything?
Does it matter.

Take your brake pad and adjust them so they are rubbing just a little
on the rim on one side. I sure can't notice that. Can you? Does it
matter? I think it does.

Dear John,

I think that you're misunderstanding the scale involved.

It's approximately 1000 mm from your hip to the floor.

A 175 mm crank drops 2.5 mm lower than a 172.5 mm crank.

So the leg extension difference is about 997.5 mm versus 1000.0 mm, or
0.25%.

A finger is approximately 20 mm wide.

So for roughly the same scale effect, tighten the vise only about 0.05
mm, not 2.5 mm.

That 0.05 mm is only about two thousandths of an inch, the thickness
of a sheet of the thin paper used in telephone books.

Carl, I think you are misunderstanding the scale involved. Your joints
can move X distance. If you set up the bike so they are at the edge
of the range of motion, that is at X, and they are forced to move X
+2mm, they will hurt.

Hope that clears it up for you.

That's why if X is 1meter I couldn't tell the difference between 60cm
and 61cm -- they both will feel short. But I can tell the difference
between 1meter and 100.3cm -- one feels OK and the other too long.
And 101cm and 102cm wouldn't feel very different -- both would feel
too long.

Dear John,

If things were ever actually set up at the very farthest end of
comfortable motion, then they'd probabably start hurting within an
hour or less.

Riders commonly range in height from 64 inches to 76 inches (5'4" to
6'4"😉. That's a height and presumable leg length range in which the
tallest rider's leg is 19% longer than the shortest rider's leg.

But these rider pedal without noticeable discomfort using cranks that
commonly range from only 165 mm to 180 mm--the longest crank is only
about 9% longer than the shortest.

To match common notions about sensitive ranges of motion, a 76-inch
tall rider would need 196 mm cranks to match the motion of the 64-inch
tall rider riding comfortably with 165 mm cranks:

64/165 ~= 0.388 ~= 76/196

But few 6'4" riders are demanding 196 mm cranks. They're usually happy
with 175~180 mm cranks, 21 to 16 mm shorter.

Things aren't much better if we reverse them.

Suppose that the 76-inch rider's motion is ideal with 180 mm cranks.
Then the 5'4" rider needs 152 mm cranks to match that motion:

76/180 ~= 0.422 ~= 64/152

But hardly any 5'4" riders are demanding 152 mm cranks. They're
usually happy with 165~170 mm cranks, 13 to 18 mm longer.

The three joints--hip, knee, ankle--have little trouble accomodating
to a tenth of an inch difference in crank length. Human legs do not
function with tolerances of only a tenth of an inch of regular motion
at the ball of the foot.

It's mostly the minds of the riders that have trouble accomodating.

Posters often ruefully confess that they never noticed a crank with
mismatched 172.5 and 175.0 arm. Even more posters admit that they
can't tell what size cranks are mounted on an unfamiliar bicycle.

But I know of no blind tests in which riders have showed that they
could tell the difference between cranks that varied only 2.5 mm.

I don't doubt the sincerity of the belief that a tenth of an inch
makes a noticeable difference.

I just remain skeptical that riders can tell when someone else
randomly switches in a 175 mm arm for a 172.5 mm arm, much less
demonstrate a speed difference. I think that knowing there's a
difference is what matters, not the actual difference.

Of course, I could be wrong, so . . .

For a simple experiment, put a piece of tape with 1/10th inch lines on
your bike seat. Close your eyes, sit on the saddle a dozen times, and
have your wife note where your pants meet the tape. How much does that
end of the hip-knee-ankle complex move around?

For a more convincing experiment, have a friend or a local bike shop
randomly mount a pair of different length left crank arms of the same
brand on your bike with the same pedal, one of them your usual length
and the other 2.5 mm longer (or shorter--either way is fine).

Do it over two weeks. Try not to look at the cranks while you ride.
Have your friend or the local bike shop pick the crank to be mounted
by a coin flip.

Then compare your daily list of what you felt you were riding with the
daily list from your friend or local bike shop.

If you really can tell the difference, you'll have a very interesting
post for RBT.

Cheers,

Carl Fogel

On Sun, 18 Feb 2007 17:22:59 -0500, John Forrest Tomlinson
<[email hidden]> wrote:

[snip]

Quoted message said:

Quoted message said:

an inch shorter by the end of the day, due to the compression of our
spinal disks.

I don't change height anywhere nearly that amount.

[snip]

Dear John,

The cartilage disks between our vertebrae expand every night because
there's no weight compressing them. There are over two dozen of these
disks, with various widths and normal pressures on them. If only
twenty of them compresses an average of a twentieth of an inch, you'll
lose an inch of height.

Height measurements in the morning are routinely noticeably greater
than in the evening after a day spent upright. But height measurements
are rarely taken right after we get out of bed, so the phenomenon
isn't easily noticed.

The effect is even more pronounced for astronauts, who often gain two
inches in height during long missions.

http://www.unexplainable.net/artman/publish/article_599.shtml

As the page mentions, "a centimeter or two" of height difference is
quite common on earth, about half an inch to an inch.

(In space, the effect is even greater because our curved spines are
freed to straighten out more.)

Have your wife use a ruler to mark your height tomorrow morning
against a door jamb and then do the same thing again before you go to
bed. You may be surprised.

Cheers,

Carl Fogel

Quoted message said:

If things were ever actually set up at the very farthest end of
comfortable motion, then they'd probabably start hurting within an
hour or less.

Let's play word games. At the limit of range of motion at which the
activity can be repeated thousands of times w/o it hurting.

So. I'm not saying I can hope on a bike and instantly say "Oh, the
saddle is a couple mm too high. But after repeating the motion
beyound what if appropriate several thousand times I notice.

Quoted message said:

Riders commonly range in height from 64 inches to 76 inches (5'4" to
6'4"😉. That's a height and presumable leg length range in which the
tallest rider's leg is 19% longer than the shortest rider's leg.

But these rider pedal without noticeable discomfort using cranks that
commonly range from only 165 mm to 180 mm--the longest crank is only
about 9% longer than the shortest.

To match common notions about sensitive ranges of motion, a 76-inch
tall rider would need 196 mm cranks to match the motion of the 64-inch
tall rider riding comfortably with 165 mm cranks:

64/165 ~= 0.388 ~= 76/196

But few 6'4" riders are demanding 196 mm cranks. They're usually happy
with 175~180 mm cranks, 21 to 16 mm shorter.

This proves nothing about sensitivity to changes in crankarm length.
But it's a lot of words, so I guess you're trying to distract us.

Quoted message said:

Things aren't much better if we reverse them.

Suppose that the 76-inch rider's motion is ideal with 180 mm cranks.
Then the 5'4" rider needs 152 mm cranks to match that motion:

76/180 ~= 0.422 ~= 64/152

But hardly any 5'4" riders are demanding 152 mm cranks. They're
usually happy with 165~170 mm cranks, 13 to 18 mm longer.

The three joints--hip, knee, ankle--have little trouble accomodating
to a tenth of an inch difference in crank length. Human legs do not
function with tolerances of only a tenth of an inch of regular motion
at the ball of the foot.
It's mostly the minds of the riders that have trouble accomodating.

So how is it that I can set up a new frame, with the same seatpost and
seat from my old bike (and cranks, and BB and pedals), in the same
clothes that I rode on my old bike, ride it once and feel my knee is
tight at the end of the ride, then look really carefully at it and see
either the seatpost slipped or I made a tiny error in measurement.

Am I imaginging it?

Well I guess I must be, huh.

Quoted message said:

Posters often ruefully confess that they never noticed a crank with
mismatched 172.5 and 175.0 arm. Even more posters admit that they
can't tell what size cranks are mounted on an unfamiliar bicycle.

Posters in this group say all sorts of things.

But keep repeating things and writing longer and longer calculations
and I guess I'll get tired of it.

Quoted message said:

But I know of no blind tests in which riders have showed that they
could tell the difference between cranks that varied only 2.5 mm.

I haven't set up blinds tests but I've noticed errors in bike set up
after the fact and I've noticed differneces in orthotics that I
believed were the same. Please write some long long stuff explaning
why that is invalid.

Quoted message said:

I don't doubt the sincerity of the belief that a tenth of an inch
makes a noticeable difference.

So it's just random that I notice the knee tightness after riding
orthotics that were a little thicker than I thought. I'm sincere in
deluding myself that I happened to notice a difference that I didn't
think existed earlier, but does exist.

WTF are you rambing about?

Quoted message said:

I just remain skeptical that riders can tell when someone else
randomly switches in a 175 mm arm for a 172.5 mm arm, much less
demonstrate a speed difference. I think that knowing there's a
difference is what matters, not the actual difference.

I know you remain skeptical. You keep right it over and over again.
Thanks,

Quoted message said:

Of course, I could be wrong, so . . .

Quoted message said:

For a simple experiment, put a piece of tape with 1/10th inch lines on
your bike seat. Close your eyes, sit on the saddle a dozen times, and
have your wife note where your pants meet the tape. How much does that
end of the hip-knee-ankle complex move around?

This is irrelevant. I notice the problem in riding, not in sitting
statically.

Quoted message said:

For a more convincing experiment, have a friend or a local bike shop
randomly mount a pair of different length left crank arms of the same
brand on your bike with the same pedal, one of them your usual length
and the other 2.5 mm longer (or shorter--either way is fine).

I've done the experiments in an unplanned way with bike set-up error
or seatpost slipping, and with a change in orthotics. Please rather
than rambling on and on, explain the problem with those experiences.
They were unplanned.

Quoted message said:

Do it over two weeks. Try not to look at the cranks while you ride.
Have your friend or the local bike shop pick the crank to be mounted
by a coin flip.

You dumbass -- did you read any of the two examples I gave that were
really blind about tiny changes in saddle height?

Please just write and write and write but don't read and think about
what I say. I expect that from you.
--
JT
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Quoted message said:

On Sun, 18 Feb 2007 17:22:59 -0500, John Forrest Tomlinson
<[email hidden]> wrote:

[snip]

Quoted message said:

Quoted message said:

an inch shorter by the end of the day, due to the compression of our
spinal disks.

I don't change height anywhere nearly that amount.

[snip]

Dear John,

The cartilage disks between our vertebrae expand every night because
there's no weight compressing them. There are over two dozen of these
disks, with various widths and normal pressures on them. If only
twenty of them compresses an average of a twentieth of an inch, you'll
lose an inch of height.

Do you actually think or do you just repeat things you read once.
I've meaured myself many times and there are small changes but not
that much over the course of the day. I'm comparing measurements
standing after being awake for ten or fifteen minutes and after being
awake for ten or so hours.

Oh yeah, I didn't measure myself in a double-blind study, so the
measurements I've made are invalid and the generalization you make is
completely true.

Baloney dear Carl.

--
JT
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On Feb 18, 2:15 pm, [email hidden] wrote:

<snipped>

- on leg length differences, and so on -

Quoted message said:

When walking or running, few of us can tell which of our legs is
shorter. Indeed, most of us don't even know if we're waddling around
on slightly mismatched legs, any more than we notice that we're up to
an inch shorter by the end of the day, due to the compression of our
spinal disks.

About "an inch shorter" has been my experience in early AM v. PM
height measurments. The first few times I tried this, the results,
just a bit less than an inch of "shrinkage", really surprised me.

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

Quoted message said:

* * Chas said:

One last note that no one has mentioned in this thread, with longer
cranks, your knee comes up higher and I've seen problems mentioned

about

Quoted message said:

Quoted message said:

that issue.

Wait, are you arguing that long cranks are bad (the comment above
seems to support that) or that long cranks can be noticed due to the
interfence above (which seems to contradict things you said earlier)?
--
JT

PLEASE re-read what I said in 2 or 3 messages.

What I said was that while some people are probably able to detect a
difference in crank lengths of 2.5mm most people probably couldn't.

I said nothing pro or con about specific crank lengths.

I suggested that no one in this thread had addressed the issue of longer
cranks coming up higher at the top of the rotation and that I had
heard/read comments that this can be a problem for some riders:

180mm cranks are 3/8" lower at the bottom of the rotation but they are
also 3/8" higher at the top of the rotation.

I can appreciate that you came up with a solution for your physical
problems.

I had my own cycling problem that I found a solution for. In 1978 I got
started about 5-10 minutes late on a century ride. I was hammering to
catch up to some friends. About 25 miles out my knees started killing me.
I had to abandon the ride and work my way back home.

Off and on for the next 15 years I had to give up riding and cross
country/telemark skiing because of knee pain. I have bone spurs under my
knee caps.

I tried different crank lengths and toeclip lengths seat heights an a
bunch of other things with no success. I saw a number of specialists and
went through physical therapy but nothing helped except giving up my
sports activities.

A friend who was a serious racer suggested that I stood pigeon toed with
my toes pointing out and my heels in and that I should adjust my toeclips
so that my heels were angled inward. I made the change and it helped the
problem.

I started riding wide Sakae LowFat MTB pedals on all of my bikes. That
made a big difference too.

Chas.

On Sun, 18 Feb 2007 21:54:17 -0500, John Forrest Tomlinson
<[email hidden]> wrote:

[snip]

Quoted message said:

So how is it that I can set up a new frame, with the same seatpost and
seat from my old bike (and cranks, and BB and pedals), in the same
clothes that I rode on my old bike, ride it once and feel my knee is
tight at the end of the ride, then look really carefully at it and see
either the seatpost slipped or I made a tiny error in measurement.

Am I imagining it?

Well I guess I must be, huh.

[snip]

Dear John,

Yes, you probably are. No, you probably won't believe it.

A classic sign of princess-in-the-pea syndrome is the belief that a
different pair of pants or slightly thicker socks could cause knee
problems.

Doctors are used to patients who insist that tinier and tinier changes
have amazingly large effects.

It's hard to remember that these hypochondriac patients are sincere.
They're so busy trying to identify tiny changes in how they feel that
they both magnify whatever they happen to feel and equate it with
whatever recent change they happen to have made.

The basis of most snake oil remedies is that the patients who happen
to improve quite naturallly give all the credit to whatever elixir or
therapy they were using at the time.

Poor Eddy Mercx can be seen in videos, stopping to fiddle with his
seat height during Paris-Roubaix. Given the pain of his back injuries,
it's understandable that he constantly adjusted his seat height in
hopes that something would help.

But it's just an example of what W. Edwards Deming illustrated with
his funnel-and-marble demonstration.

If you set up a funnel on a stand and drop one marble through it, you
can see where the marble lands near a target after it rattles through
the wide nozzle of the funnel.

If you move the funnel-stand after every drop to try to make the next
marble hit the target, you get a much worse result than you would if
you averaged a dozen marbles.

You simply can't do any better than the average determined by how wide
the funnel is. Each marble hits randomly somewhere inside a ring.

Chasing each random hit only widens the average concentration. Any
target shooter is painfully aware of this.

Unfortunately, that's what we often do because of practical limits. We
want to ride faster or do something about knee pain, so we try a
different [seat/crank/handlebar/frame/gear/shoe/pedal/whatever].

Normal random variation means that in the next two weeks we're likely
to have a [sore-back/fast-time/tight-knee/happy-ride].

We mistakenly attribute the random result that would have happened
anyway to whatever we happened to be adjusting at the time, and we
refuse to test long enough to eliminate random variation.

It's much quicker to do things this way than to spend months
collecting data, and it's very satisfying to know that we are [very
sensitive/slightly faster/avoiding injury/better equipped].

The process works best where things matter least.

No one is immune to this sort of thing. No matter what I think, I
can't imagine using anything except 175 mm cranks--anything shorter
would surely be inefficient, while anything longer would undoubtedly
flex my joints painfully!

(Luckily, I never looked at the cranks on the bikes that I rode for my
first 50,000 miles--they probably had 172.5 mm or even 170 mm cranks
and must have been terrible.)

To complicate things, chasing random variation and self-exaggerated
illnesses can turn out to be right--there's a faint possibility that
your knee is so delicate that a crank a tenth of an inch longer will
ruin it. But normal knees happily accept much larger variations.

People who fit things are cursed by this problem. Any small change
that they make may well get the blame or credit for something
completely unrelated.

An awful lot of bike-fit theories suggest Langmuir's laws of bad or
pathological science:

1. The maximum effect that is observed is produced by a causative
agent of barely detectable intensity, and the magnitude of the effect
is substantially independent of the intensity of the cause.

2. The effect is of a magnitude that remains close to the limit of
detectability; or, many measurements are necessary because of the very
low statistical significance of the results.

3. Claims of great accuracy.

4. Fantastic theories contrary to experience.

5. Criticisms are met by ad hoc excuses thought up on the spur of the
moment.

6. Ratio of supporters to critics rises up to somewhere near 50% and
then falls gradually to oblivion

http://www.cs.princeton.edu/~ken/Langmuir/langB.htm#Characteristic%20Symptoms

Most people are quite comfortable with left and right shoes of the
same size, even though they have left and right feet that are
measurably different in length and width on a shoe-store scale.

I hope that's enough words for you.

Cheers,

Carl Fogel

John Forrest Tomlinson said:

Quoted message said:

On Sun, 18 Feb 2007 17:22:59 -0500, John Forrest Tomlinson
<[email hidden]> wrote:

[snip]

Quoted message said:

>an inch shorter by the end of the day, due to the compression of our
>spinal disks.

I don't change height anywhere nearly that amount.

[snip]

Dear John,

The cartilage disks between our vertebrae expand every night because
there's no weight compressing them. There are over two dozen of these
disks, with various widths and normal pressures on them. If only
twenty of them compresses an average of a twentieth of an inch, you'll
lose an inch of height.

Do you actually think or do you just repeat things you read once.
I've meaured myself many times and there are small changes but not
that much over the course of the day. I'm comparing measurements
standing after being awake for ten or fifteen minutes and after being
awake for ten or so hours.

Oh yeah, I didn't measure myself in a double-blind study, so the
measurements I've made are invalid and the generalization you make is
completely true.

Baloney dear Carl.

Dear John,

I happily repeat what doctors have repeatedly tested and agree on.

In this case, I was startled to have a doctor measure my height at
more than it normally is. At the age of thirty, I doubted that I was
growing.

Out of curiosity, why were you measuring yourself repeatedly during
the course of the day if you were unaware of the phenomenon?

When can we expect to read your paper on how mistaken medical science
is about your spine?

Cheers,

Carl Fogel

In article <[email hidden]>,

Ben C said:

Tim McNamara said:

In article <[email hidden]>,

ddog said:

On Feb 18, 7:40 am, Lou Holtman <[email hidden]> wrote:
> It's 2.5 mm difference for Gods sake. Two different socks have
> the same effect.
>
> Lou

If God's sake does not include leverage, turning limits, and
biomechanical equilibrium, in a narrow minded overly simplistic
viewpoint you may be right. But because there are always limits
that effect different people differently, overly simplistic one
liners are always wrong and can hurt some people if they weigh
your comments as legitimate arguments.

Remaining agnostic on the god aspect, I'll chime in that "it's only
a 2.5 mm difference." Now, in my case, with a measured
leg-to-crotch distance of 910 mm, that 2.5 mm difference is about
0.27% overall. That seems unlikely to be a significant difference.
Switching shoes can easily result in that much difference.

Actually since you point that out, different shoes _do_ feel
different, even similar shoes with only a very small change in sole
thickness. It feels like the saddle is too high or too low, although
you quickly forget about it after riding off.

In my case, I have shoes with about an 8 mm range of sole thickness.
It's mildly noticeable for a few pedal strokes. Over 75-80 mile rides,
it makes no difference that I can notice.

Each of my bikes probably has more difference in position than 2.5 mm in
most dimensions of fit. I've not really put a whole lot of time and
energy into micromanaging fit across all my bikes. As long as it's
comfortable and close enough, it's close enough.

In article <[email hidden]>,

John Forrest Tomlinson said:

Quoted message said:

If things were ever actually set up at the very farthest end of
comfortable motion, then they'd probabably start hurting within an
hour or less.

Let's play word games. At the limit of range of motion at which the
activity can be repeated thousands of times w/o it hurting.

YMMV, everybody's different, and other boiler plate disclaimers.
Frankly that sounds like a poor way to set up your bike. I haven't seen
you on your bike, so I can't comment about your fit. And frankly, it's
your bike and if it works for you, then that's what counts rather than
the armchair opinion of a guy 1000 miles away.

Quoted message said:

So. I'm not saying I can hope on a bike and instantly say "Oh, the
saddle is a couple mm too high. But after repeating the motion
beyound what if appropriate several thousand times I notice.

Interestingly enough, that the exact opposite from what would be normal
and runs counter to a well established body of experimental data
regarding motor perception. You'd expect the difference to be
noticeable immediately, and to quickly disappear as your motor cortex
adapts to the new situation.

From a personal experience, I am sure I can notice a saddle height
change of 1 cm, e.g. from a slipping seat post. I also know that I've
gotten on the bike and it has felt different- saddle too high or too
low- and I haven't changed anything and nothing has slipped. If I ride
one bike one day and another bike the next day, it feels immediately
different- but noticing that difference has gone way in a block or two.
But even big changes like that can go unnoticed, since I'm riding along
and talking with my friends, looking at the scenery, trying not to get
run over by the latte-sipping-cell phone talking-idiot in the land
missile, etc.

Carl Fogel wrote, to John Forrest Tomlinson:

Quoted message said:

Have your wife use a ruler to mark your height tomorrow morning
against a door jamb and then do the same thing again before you go to
bed.

Wife? I though JFT was a bicycle racer.

Tim McNamara said:

I don't know if this has been studied. The question is whether a leg
extension difference of 2.5 mm would be haptically discernible. I
rather tend to doubt it and suspect that the difference would fall below
the threshold of least discernible difference.

However, there are certainly individual differences in sensory acuity,
so I also wouldn't rule it out with confidence.

Rather than put a piece of tape on the seat post to mark the location as
some do, I record the height of the exposed part of the seat post. Over the
years, I have had about two occasions where, because the seat post was
removed or moved for whatever reason, I've had to fiddle with my saddle
height on the road until it felt right to me. The seat post is unmarked, so
positioning was essentially blind. Both times, when I got home and measured
the exposed section of seat post, it matched what was in my records exactly
to the nearest millimeter. Dumb luck? I don't think so.

Similarly, last year, I decided that the saddle height on my mountain bike
didn't feel quite right since I swapped out the pedals with clips and straps
with clipless pedals a couple of years ago. I had also deliberately kept
the saddle a bit low to help deal with bumps, but was re-thinking that idea.
I went out on a ride and fiddled with the height. I was surprised at how
small the difference was between feeling a bit too high and not quite high
enough. I think I started out moving the post up about 5-7 mm (just eyeing
it), but that was too much and I went up and down in smaller increments
about three more times before I quit. When I was using clips and straps, I
could feel the difference in height between using my running shoes and my
slotted cleat road shoes.

I can definitely feel the difference between the 175s on my mountain bike
and the 170s on my road bike. I use a lower saddle relative to the bottom
bracket with the 175s because it feels better to have the bottom of the
stroke similar to the shorter cranks. But then the top part of the stroke
is 1 cm higher, and there is more knee bend. I like the 170s a lot more.
If my mountain bike cranks ever break, 170s will go on.

Because of the greater knee bend required, I see longer cranks as similar to
doing deeper one-legged squats vs. shallower one-legged squats. It's
personal preference within the safe range, but at some point, deeper squats
and long enough cranks are more likely to case injury.

I won't argue that being able to feel the difference in height means that
there is also a performance difference except that I think I can perform
better when I'm more comfortable.

On Feb 18, 5:27 pm, "David L. Johnson" <[email hidden]>

Quoted message said:

Joel Mayes said:

David L. Johnson said:

The last concern is overblown. Very few such conversions have less than
a 45-degree lean angle before the pedal contacts the road, and if you
are leaning over more than that you are on the way down, anyway. Lots
of people experience hitting a pedal and going down in a corner, but
wrongly infer that the pedal strike caused the fall. Usually it's the
other way around.

Quoted message said:

This also assumes that the corner you are in is perfectly flat, if the
road slopes upwards into the corner your pedal clearance can be
dramatically shortened.

That logic doesn't work, since if you are on a sloped road (negatively
sloped with respect to the corner, of course) you will still slide out
when your angle with the road is more than 45 degrees.

My fixed gear conversion, which is pretty typical
for a low-BB road bike, has only 30 degree cornering
clearance, I just measured it. (270mm BB height, 170mm
cranks, Ritchey MTB clipless pedals). I've definitely
clipped a pedal on it, although I've never fallen down as
a result. I also have a Cannondale that was originally a
touring bike (lowish BB) and converted from 27" to 700c
(lowers by ~5mm) and has 175mm cranks. This is not a fixie,
but I've clipped pedals on it while pedaling around corners,
often enough to think that I should really swap the cranks
for the identical 170mm ones on my MTB. I'll probably get
to doing it after falling down someday.

I have noticed that the pedal clipping happens more on
reverse banked corners like Joel mentioned - for the
Norcal crowd, I clipped a pedal more than once going
around the 120 deg hairpin in the Santa Cruz Criterium.
I think this is psychological: because I am not crazy/skilled
enough to be at the limits of traction, I'll go into a
reverse banked corner at about the same speed as a flat
corner, so at a greater effective lean angle.

Ben

In article
<[email hidden]>,

Scotty said:

What is the theory behind picking a crank arm length ?
So many factors are involved. Frame size, leg length, or femur length, shoe
size, riding style. Everyone put in their opinions if they wish.

Guys who are much taller notice immediately how much
better they are when switching to 180-190-200 mm
cranks. Shorter women notice immediately how much
better they are with 155-160 mm cranks. Nobody else
notices.

--
Michael Press

In article <[email hidden]>,

A Muzi said:

Quoted message said:

Lou Holtman said:

How can anybody find out scientific that a 2.5 mm change in cranklength
make a difference? Do the people who say they can
feel that difference also adjust there saddle height every time they
wear different shorts with different paddings or different shoes? I
think there is an upper and a lower limit (there has to be) and I am
convinced that for most people 2.5 mm is within those limits.

John Forrest Tomlinson said:

Lou, if you can't feel something does that mean it doesn't matter?

That's a very good question, the answer to which is not at all clear to me.

Certainly most riders cannot tell. I doubt there's any objective
performance, comfort or other significant difference. That to one side,
as I noted earlier, some riders insist it is a crucial dimension.
Whether that effect is real or imagined, a rider who believes his
equipment is better, or better suited, performs better. I'm sure you
noticed that in your years of competition.

At the end of the day there's no harm. If a rider insists that he'll be
faster with 177.5 than 175 he's welcome to that opinion. If you swapped
+/-2.5mm cranks under most riders, they would not know.

I notice this much difference in saddle height, so I
might notice +2.5 mm in the cranks.

--
Michael Press

In article
<[email hidden]>,

Quoted message said:

John Forrest Tomlinson said:

Quoted message said:

On Sun, 18 Feb 2007 14:37:40 -0500, John Forrest Tomlinson
<[email hidden]> wrote:

>On Sun, 18 Feb 2007 11:02:33 -0800, "* * Chas"
><[email hidden]> wrote:
>
>>Look at a ruler. Now hold your thumb and forefinger 2.5mm (1/8"😉 apart and
>>compare that gap with the length of your legs and feet combined.
>
>Place your finger into the opening of a vise that is the same width as
>your finger. Now tighten the vise 2.5mm. Do you notice anything?
>Does it matter.
>
>Take your brake pad and adjust them so they are rubbing just a little
>on the rim on one side. I sure can't notice that. Can you? Does it
>matter? I think it does.

Dear John,

I think that you're misunderstanding the scale involved.

It's approximately 1000 mm from your hip to the floor.

A 175 mm crank drops 2.5 mm lower than a 172.5 mm crank.

So the leg extension difference is about 997.5 mm versus 1000.0 mm, or
0.25%.

A finger is approximately 20 mm wide.

So for roughly the same scale effect, tighten the vise only about 0.05
mm, not 2.5 mm.

That 0.05 mm is only about two thousandths of an inch, the thickness
of a sheet of the thin paper used in telephone books.

Carl, I think you are misunderstanding the scale involved. Your joints
can move X distance. If you set up the bike so they are at the edge
of the range of motion, that is at X, and they are forced to move X
+2mm, they will hurt.

Hope that clears it up for you.

That's why if X is 1meter I couldn't tell the difference between 60cm
and 61cm -- they both will feel short. But I can tell the difference
between 1meter and 100.3cm -- one feels OK and the other too long.
And 101cm and 102cm wouldn't feel very different -- both would feel
too long.

Dear John,

If things were ever actually set up at the very farthest end of
comfortable motion, then they'd probabably start hurting within an
hour or less.

Riders commonly range in height from 64 inches to 76 inches (5'4" to
6'4"😉. That's a height and presumable leg length range in which the
tallest rider's leg is 19% longer than the shortest rider's leg.

But these rider pedal without noticeable discomfort using cranks that
commonly range from only 165 mm to 180 mm--the longest crank is only
about 9% longer than the shortest.

To match common notions about sensitive ranges of motion, a 76-inch
tall rider would need 196 mm cranks to match the motion of the 64-inch
tall rider riding comfortably with 165 mm cranks:

64/165 ~= 0.388 ~= 76/196

But few 6'4" riders are demanding 196 mm cranks. They're usually happy
with 175~180 mm cranks, 21 to 16 mm shorter.

Things aren't much better if we reverse them.

Suppose that the 76-inch rider's motion is ideal with 180 mm cranks.
Then the 5'4" rider needs 152 mm cranks to match that motion:

76/180 ~= 0.422 ~= 64/152

But hardly any 5'4" riders are demanding 152 mm cranks. They're
usually happy with 165~170 mm cranks, 13 to 18 mm longer.

The three joints--hip, knee, ankle--have little trouble accomodating
to a tenth of an inch difference in crank length. Human legs do not
function with tolerances of only a tenth of an inch of regular motion
at the ball of the foot.

It's mostly the minds of the riders that have trouble accomodating.

Posters often ruefully confess that they never noticed a crank with
mismatched 172.5 and 175.0 arm. Even more posters admit that they
can't tell what size cranks are mounted on an unfamiliar bicycle.

But I know of no blind tests in which riders have showed that they
could tell the difference between cranks that varied only 2.5 mm.

I don't doubt the sincerity of the belief that a tenth of an inch
makes a noticeable difference.

I just remain skeptical that riders can tell when someone else
randomly switches in a 175 mm arm for a 172.5 mm arm, much less
demonstrate a speed difference. I think that knowing there's a
difference is what matters, not the actual difference.

Of course, I could be wrong, so . . .

For a simple experiment, put a piece of tape with 1/10th inch lines on
your bike seat. Close your eyes, sit on the saddle a dozen times, and
have your wife note where your pants meet the tape. How much does that
end of the hip-knee-ankle complex move around?

For a more convincing experiment, have a friend or a local bike shop
randomly mount a pair of different length left crank arms of the same
brand on your bike with the same pedal, one of them your usual length
and the other 2.5 mm longer (or shorter--either way is fine).

Do it over two weeks. Try not to look at the cranks while you ride.
Have your friend or the local bike shop pick the crank to be mounted
by a coin flip.

Then compare your daily list of what you felt you were riding with the
daily list from your friend or local bike shop.

If you really can tell the difference, you'll have a very interesting
post for RBT.

My saddle is as high as it can go, and no higher.
Higher means my hips rock, I lose power, and I get
uncomfortable. With the saddle at the upper limit I am
as comfy as in my easy chair. Can't spend unlimited
time in either. Now extend the cranks 2.5 mm and I
suffer from having a saddle that is too high.

Hope this clears it up for you.

--
Michael Press