Re: RH/L:H pedal threads

[David L. Johnson]

On Sat, 09 Apr 2005 02:26:26 +0000, Leo Lichtman wrote:

> Why are pedals threaded RH on the right side, and LH on the left side? If
> the idea is to keep the pedals from working loose as you ride, I think
> they've got it backwards.

No, they don't.

> The torque applied to the pedal shafts by the
> bearing friction, in the existing system, tends to loosen them.

No, it doesn't. You have to think about how the bearing balls move in the
system to see why.

> But that
> friction is so low compared to the tightness of a properly installed
> pedal that I don't think you could unscrew a pedal by spinning it.

It did happen. But this is ancient history, since all bikes have had the
pedals this way since the very early part of the 20th century (the idea
being introduced by the Wright brothers).

People who adapt single-bike cranks to tandems have trouble with pedals
unscrewing, since three of the 4 crank arms are the "wrong" side.

>
> What am I missing? They used to have left handed lug nuts on cars, and
> they don't do that anymore. Could bicycle technology be THAT far behind?

Lug nuts are different. However, a tapered fitting like a lug nut would
also work, as has occasionally been mentioned here.

--

David L. Johnson

__o | And though I have the gift of prophecy, and understand all
_`\(,_ | mysteries, and all knowledge; and though I have all faith, so
(_)/ (_) | that I could remove mountains, and have not charity, I am
nothing. [1 Corinth. 13:2]

 

[Benjamin Lewis]

David L. Johnson wrote:

> On Sat, 09 Apr 2005 02:26:26 +0000, Leo Lichtman wrote:
>> The torque applied to the pedal shafts by the
>> bearing friction, in the existing system, tends to loosen them.
>
> No, it doesn't. You have to think about how the bearing balls move in
> the system to see why.

It has nothing to do with the bearings; it's because the pedal spindle
precesses in the crank. If your pedals were loose enough, and the bearings
seized up completely, the pedals *would* unscrew.

--
Benjamin Lewis

Evelyn the dog, having undergone further modification, pondered the
significance of short-person behavior in pedal-depressed panchromatic
resonance and other highly ambient domains... "Arf", she said.

 

[Martyn Aldis]

In message <[email protected]>, David L.
Johnson <[email protected]> writes
>On Sat, 09 Apr 2005 02:26:26 +0000, Leo Lichtman wrote:
>
>> Why are pedals threaded RH on the right side, and LH on the left side? If
>> the idea is to keep the pedals from working loose as you ride, I think
>> they've got it backwards.

>>


For a short explanation of pedal threading see:

http://sheldonbrown.com/gloss_p.html#pedal

>
>> The torque applied to the pedal shafts by the
>> bearing friction, in the existing system, tends to loosen them.
>

Yes, but it is overpowered.

>No, it doesn't. You have to think about how the bearing balls move in the
>system to see why.

The bearing friction is in the same rotational direction ball bearing or
plain bearing (like Chopper pedals).

The bearing friction is in the direction the OP suggests but the
precession effect at the threaded interface is more powerful and opposes
the bearing drag.

I fell into this one a few weeks ago in a posting concerning bottom
bracket cups. We can comfort ourselves that we are not the first nor
will we be the last.


--

Martyn Aldis, e-mail [email protected]
==============================================================================

 

[[email protected]]

Benjamin Lewis writes:

>>> The torque applied to the pedal shafts by the bearing friction, in
>>> the existing system, tends to loosen them.

>> No, it doesn't. You have to think about how the bearing balls move
>> in the system to see why.

> It has nothing to do with the bearings; it's because the pedal
> spindle precesses in the crank. If your pedals were loose enough,
> and the bearings seized up completely, the pedals *would* unscrew.

I think you jumped the gun. Re-read that sentence and you'll see that
the balls in a pedal bearing rotate opposite from the spindle. It is
the same effect that unscrews the pedal on a left crank with a right
hand thread (or a right pedal with a left hand thread).

It makes no difference how tight you make the pedal, it will move in
the threads as long as it has a flat face on its spindle. To prove
that, look at the either crank face with the pedal removed and notice
an eroded area where the shoulder of the pedal spindle was moving.
This motion unscrews a pedal opposite to the way the OP suggested.

The conical taper on a pedal shaft would prevent this motion and
therefore unscrewing the pedal regardless of thread direction.

[email protected]

 

[Leo Lichtman]

<[email protected]> wrote: (clip) It makes no difference how
tight you make the pedal, it will move in the threads as long as it has a
flat face on its spindle. (clip)
^^^^^^^^^^^^^^^^
The wording of that statement confused me at first, so let me help anyone
else who has the same difficulty. The "flat face" Jobst is referring to is
the shoulder that tightens against the crank arm--NOT the flat faces on the
sides of the pedal spindle that the wrench fits.

 

[Martyn Aldis]

In message <[email protected]>,
[email protected] writes
>Benjamin Lewis writes:
>
>>>> The torque applied to the pedal shafts by the bearing friction, in
>>>> the existing system, tends to loosen them.
>
>>> No, it doesn't. You have to think about how the bearing balls move
>>> in the system to see why.
>
>> It has nothing to do with the bearings; it's because the pedal
>> spindle precesses in the crank. If your pedals were loose enough,
>> and the bearings seized up completely, the pedals *would* unscrew.
>
>I think you jumped the gun. Re-read that sentence and you'll see that
>the balls in a pedal bearing rotate opposite from the spindle. It is
>the same effect that unscrews the pedal on a left crank with a right
>hand thread (or a right pedal with a left hand thread).

Not sure what you mean here Jobst. The balls rotate about their own axis
opposite to the spindle but don't they travel round the spindle axis
just like the planets in an epicyclic hub gear?

Anyway, the balls are irrelevant aren't they?
The friction from the bearing system plain, ball or whatever will be in
the same sense as the OP suggested and against the precession effect so
as Benjamin says, if the bearing friction is high enough it will
overcome other effects and unscrew the pedal just like a spanner. I have
found wads of horse hair in pedals used without dust caps so I suppose
this could happen on a very badly looked after bike.

I wonder if this threading problem really started with cycle parts.
Steam engines used cranks a long time before. According to this page the
crank was patented for an atmospheric engine in 1780 which led to Watt
use planet gearing for a while.

http://www.kbsm.org/historic/watt.stm
--

Martyn Aldis, e-mail [email protected]
==============================================================================

 

[[email protected]]

Martyn Aldis writes:

>>>>> The torque applied to the pedal shafts by the bearing friction,
>>>>> in the existing system, tends to loosen them.

>>>> No, it doesn't. You have to think about how the bearing balls
>>>> move in the system to see why.

>>> It has nothing to do with the bearings; it's because the pedal
>>> spindle precesses in the crank. If your pedals were loose enough,
>>> and the bearings seized up completely, the pedals *would* unscrew.

>> I think you jumped the gun. Re-read that sentence and you'll see
>> that the balls in a pedal bearing rotate opposite from the spindle.
>> It is the same effect that unscrews the pedal on a left crank with
>> a right hand thread (or a right pedal with a left hand thread).

> Not sure what you mean here Jobst. The balls rotate about their own
> axis opposite to the spindle but don't they travel round the spindle
> axis just like the planets in an epicyclic hub gear?

The point is that they rotate opposite to the spindle and the spindle
does the same as it precesses around the threaded bore.

> Anyway, the balls are irrelevant aren't they?

Not in the sense that was used here.

> The friction from the bearing system plain, ball or whatever will be
> in the same sense as the OP suggested and against the precession
> effect so as Benjamin says, if the bearing friction is high enough
> it will overcome other effects and unscrew the pedal just like a
> spanner. I have found wads of horse hair in pedals used without
> dust caps so I suppose this could happen on a very badly looked
> after bike.

There is no significant drag in the bearings of a bicycle pedal unless
its bearings are ground to a pulp. This is all misplaced logic.

> I wonder if this threading problem really started with cycle parts.
> Steam engines used cranks a long time before. According to this page
> the crank was patented for an atmospheric engine in 1780 which led
> to Watt use planet gearing for a while.

> http://www.kbsm.org/historic/watt.stm

I don't think you understand the problem nor that people haven't done
all this just to make life more difficult. It has been given much
thought and trial. Steam engines don't have pedals and use a
crosshead in changing linear motion to circular motion.

[email protected]

 

[Leo Lichtman]

"Martyn Aldis" wrote: (clip) Steam engines used cranks a long time before.
(clip)
^^^^^^^^^^^^^^^^^^^^^^
Those old engines used a crank, all right, but it had a bearing on either
side of the connecting rod, so the load did not make the crank "lean," as it
does on a bicycle pedal. Furthermore, I don't think those big old steam
engine cranks were threaded together.

 

[Benjamin Lewis]

jobst brandt wrote:

> Benjamin Lewis writes:
>
>>>> The torque applied to the pedal shafts by the bearing friction, in
>>>> the existing system, tends to loosen them.
>
>>> No, it doesn't. You have to think about how the bearing balls move
>>> in the system to see why.
>
>> It has nothing to do with the bearings; it's because the pedal
>> spindle precesses in the crank. If your pedals were loose enough,
>> and the bearings seized up completely, the pedals *would* unscrew.
>
> I think you jumped the gun. Re-read that sentence and you'll see that
> the balls in a pedal bearing rotate opposite from the spindle. It is
> the same effect that unscrews the pedal on a left crank with a right
> hand thread (or a right pedal with a left hand thread).

Yes, the same sort of effect, but the original poster is quite correct when
he says that the torque applied to the pedal shaft by bearing friction
tends to loosen them, and it is this statement to which David was
disagreeing.

Bearing movement is not a factor in the design of pedal/crank interface.
Is that more clear?

--
Benjamin Lewis

Evelyn the dog, having undergone further modification, pondered the
significance of short-person behavior in pedal-depressed panchromatic
resonance and other highly ambient domains... "Arf", she said.

 

[Tom Kunich]

"Leo Lichtman" <[email protected]> wrote in message
news:[email protected]...
>
> "Martyn Aldis" wrote: (clip) Steam engines used cranks a long time
> before. (clip)
> ^^^^^^^^^^^^^^^^^^^^^^
> Those old engines used a crank, all right, but it had a bearing on either
> side of the connecting rod, so the load did not make the crank "lean," as
> it does on a bicycle pedal. Furthermore, I don't think those big old
> steam engine cranks were threaded together.

They HAD to be put together in pieces because there weren't machines large
enough to turn one piece cranks. Like two stroke motorcycle cranks they were
built in pieces.

 

[[email protected]]

Tom Kunich <[email protected]> writes:

>>> Steam engines used cranks a long time before.

>> Those old engines used a crank, all right, but it had a bearing on
>> either side of the connecting rod, so the load did not make the
>> crank "lean," as it does on a bicycle pedal. Furthermore, I don't
>> think those big old steam engine cranks were threaded together.

> They HAD to be put together in pieces because there weren't machines
> large enough to turn one piece cranks. Like two stroke motorcycle
> cranks they were built in pieces.

BS! The crsnk pin on locomotive wheels is part of the wheel and is
not screwed in as in:

http://steamcad.railfan.net/
http://steamcad.railfan.net/bigboy.htm

[email protected]

 

[Martyn Aldis]

In message <[email protected]>,
[email protected] writes
>Martyn Aldis writes:
>
>>>>>> The torque applied to the pedal shafts by the bearing friction,
>>>>>> in the existing system, tends to loosen them.
>
>>>>> No, it doesn't. You have to think about how the bearing balls
>>>>> move in the system to see why.
>
>>>> It has nothing to do with the bearings; it's because the pedal
>>>> spindle precesses in the crank. If your pedals were loose enough,
>>>> and the bearings seized up completely, the pedals *would* unscrew.
>
>>> I think you jumped the gun. Re-read that sentence and you'll see
>>> that the balls in a pedal bearing rotate opposite from the spindle.
>>> It is the same effect that unscrews the pedal on a left crank with
>>> a right hand thread (or a right pedal with a left hand thread).
>
>> Not sure what you mean here Jobst. The balls rotate about their own
>> axis opposite to the spindle but don't they travel round the spindle
>> axis just like the planets in an epicyclic hub gear?
>
>The point is that they rotate opposite to the spindle and the spindle
>does the same as it precesses around the threaded bore.
>
>> Anyway, the balls are irrelevant aren't they?
>
>Not in the sense that was used here.
>
>> The friction from the bearing system plain, ball or whatever will be
>> in the same sense as the OP suggested and against the precession
>> effect so as Benjamin says, if the bearing friction is high enough
>> it will overcome other effects and unscrew the pedal just like a
>> spanner. I have found wads of horse hair in pedals used without
>> dust caps so I suppose this could happen on a very badly looked
>> after bike.
>
>There is no significant drag in the bearings of a bicycle pedal unless
>its bearings are ground to a pulp.

That is exactly what Benjamin and I have written and is quoted above.
The pedal friction can only unscrew a pedal that is seriously rusted up,
filled with hair or otherwise nearly stuck.

> This is all misplaced logic.

Where then is the misplaced logic? The effect Benjamin remarked upon was
totally consistent with the importance of the precession effect. You are
just responding to what you expect us to write not what we have written.
I think it is helpful to understand that the bearing friction does act
to unscrew the pedals but it will not do so except when the pedals are
nearly stuck and the threads are not tight. This is a matter of trying
to clarify the explanation and make it more palatable by not telling the
other party that they are totally wrong and/or stupid. They are correct
about bearing friction but another effect is more important.
>
>> I wonder if this threading problem really started with cycle parts.
>> Steam engines used cranks a long time before. According to this page
>> the crank was patented for an atmospheric engine in 1780 which led
>> to Watt use planet gearing for a while.
>
>> http://www.kbsm.org/historic/watt.stm
>
>I don't think you understand the problem nor that people haven't done
>all this just to make life more difficult.

Here you respond to what you assume I think and not what I have written.

> It has been given much
>thought and trial.

Did I suggest otherwise? I just suggested that maybe the thought and
trial came somewhat earlier than bicycle pedals.

> Steam engines don't have pedals and use a
>crosshead in changing linear motion to circular motion.

The precession effect does not require pedals and the use of a crosshead
is to do with the scale of a reciprocating engine not its type.

I hope you are successful in your attempts to promote redesign of the
pedal crank interface to the cycle components industry. You will need to
treat queries and objections and even attempts to clarify and support
your own explanations with more respect and civility than you do on this
group.
--

Martyn Aldis,e-mail [email protected]
==============================================================================