Re: outer diameter of a 56 tooth chainwheel ?

Discussion in 'Cycling Equipment' started by Zog The Undeniable, Mar 11, 2005.

  1. Retroed Bob wrote:
    > Anyone have a chart for this ? The one in question is a Stronglight,
    > but I don't suppose there's a lot of difference since for a specific
    > chain pitch, the size would always be he same (give or take tooth
    > variations). I am trying to figure out how much bigger the OD would
    > be for a 56 vs. a 52 (so, same question for the 52 :).


    The circumference (measured near the top of the teeth) is obviously 28"
    for the 56T and 26" for the 52T, because chain has a half-inch pitch.
    Diameter is circumference divided by pi, so the 56T is 8.91" across and
    the 52T is 8.28".
     
    Tags:


  2. JeffWills

    JeffWills Guest

    Zog The Undeniable wrote:
    > Retroed Bob wrote:
    > > Anyone have a chart for this ? The one in question is a

    Stronglight,
    > > but I don't suppose there's a lot of difference since for a

    specific
    > > chain pitch, the size would always be he same (give or take tooth
    > > variations). I am trying to figure out how much bigger the OD would


    > > be for a 56 vs. a 52 (so, same question for the 52 :).

    >
    > The circumference (measured near the top of the teeth) is obviously

    28"
    > for the 56T and 26" for the 52T, because chain has a half-inch pitch.


    > Diameter is circumference divided by pi, so the 56T is 8.91" across

    and
    > the 52T is 8.28".


    Uh, no... that gives you an approximate diameter at the midpoint of the
    tooth, roughly where the chain contacts the chainring. However, the
    difference between the chainrings is still about the same: the 56
    toother is 0.63" larger in diameter. If you're changing from a 52 to a
    56 tooth chainring, you'll have to raise your front derailleur by
    roughly 0.315", or (even more roughly) 3/8".

    That's assuming both chainrings have the same tooth profile. This is
    not a given.

    Jeff
     
  3. Leo Lichtman

    Leo Lichtman Guest

    "Retrobob" wrote: (clip) I am trying to figure out how much bigger the OD
    would be for a 56 vs. a 52 (clip)
    ^^^^^^^^^^^^^
    The stuff Zog wrote is correct. But, more simply, if all you are looking
    for is the difference in diameter between two chainrings, then it will be
    the difference in circumference divided by pi, which is (difference in
    teeth)/2pi.
     
  4. JeffWills wrote:
    > Zog The Undeniable wrote:
    >
    >>Retroed Bob wrote:
    >>
    >>>Anyone have a chart for this ? The one in question is a

    >
    > Stronglight,
    >
    >>>but I don't suppose there's a lot of difference since for a

    >
    > specific
    >
    >>>chain pitch, the size would always be he same (give or take tooth
    >>>variations). I am trying to figure out how much bigger the OD would

    >
    >
    >>>be for a 56 vs. a 52 (so, same question for the 52 :).

    >>
    >>The circumference (measured near the top of the teeth) is obviously

    >
    > 28"
    >
    >>for the 56T and 26" for the 52T, because chain has a half-inch pitch.

    >
    >
    >>Diameter is circumference divided by pi, so the 56T is 8.91" across

    >
    > and
    >
    >>the 52T is 8.28".

    >
    >
    > Uh, no... that gives you an approximate diameter at the midpoint of the
    > tooth, roughly where the chain contacts the chainring.


    Depends on the tooth profile. Most modern chainrings have rather low
    teeth for easy derailing of the chain. Track/singlespeed rings have
    taller teeth, but even then they hardly make it above the middle of the
    plates.
     
  5. A Muzi

    A Muzi Guest

    Zog The Undeniable wrote:

    > Retroed Bob wrote:
    >
    >> Anyone have a chart for this ? The one in question is a Stronglight,
    >> but I don't suppose there's a lot of difference since for a specific
    >> chain pitch, the size would always be he same (give or take tooth
    >> variations). I am trying to figure out how much bigger the OD would be
    >> for a 56 vs. a 52 (so, same question for the 52 :).

    >
    >
    > The circumference (measured near the top of the teeth) is obviously 28"
    > for the 56T and 26" for the 52T, because chain has a half-inch pitch.
    > Diameter is circumference divided by pi, so the 56T is 8.91" across and
    > the 52T is 8.28".

    I believe that calculation will give you the diameter at the
    center of the chain rivet - not the top of the tooth.

    http://www.yellowjersey.org/photosfromthepast/56TRING.JPG

    --
    Andrew Muzi
    www.yellowjersey.org
    Open every day since 1 April, 1971
     
  6. Jim Smith

    Jim Smith Guest

    A Muzi <[email protected]> writes:

    > Zog The Undeniable wrote:
    >
    >> Retroed Bob wrote:
    >>
    >>> Anyone have a chart for this ? The one in question is a Stronglight,
    >>> but I don't suppose there's a lot of difference since for a
    >>> specific chain pitch, the size would always be he same (give or
    >>> take tooth variations). I am trying to figure out how much bigger
    >>> the OD would be for a 56 vs. a 52 (so, same question for the 52
    >>> :).

    >> The circumference (measured near the top of the teeth) is obviously
    >> 28" for the 56T and 26" for the 52T, because chain has a half-inch
    >> pitch. Diameter is circumference divided by pi, so the 56T is 8.91"
    >> across and the 52T is 8.28".

    > I believe that calculation will give you the diameter at the center of
    > the chain rivet - not the top of the tooth.
    >
    > http://www.yellowjersey.org/photosfromthepast/56TRING.JPG


    Right, but the OP was looking for the change in diameter, which is
    independent of the diameter. If you increase the circumference by two
    inches, the diameter increases by 0.64 inches (2/pi) whether you start
    with a circle 8 inches, 8 meters, or 8 miles in diameter.
     
  7. Jim Smith wrote:

    > Right, but the OP was looking for the change in diameter, which is
    > independent of the diameter. If you increase the circumference by two
    > inches, the diameter increases by 0.64 inches (2/pi) whether you start
    > with a circle 8 inches, 8 meters, or 8 miles in diameter.
    >

    Reminds me of the old brain teaser (not all that difficult):

    If a worm crawls round the equator and a bird flies 2 metres above the
    worm, how much further has the bird travelled when they get back to
    their starting point?

    Most people think it's thousands of miles...it's actually about 6.3 metres.
     
  8. Jim Smith

    Jim Smith Guest

    Zog The Undeniable <[email protected]> writes:

    > Jim Smith wrote:
    >
    >> Right, but the OP was looking for the change in diameter, which is
    >> independent of the diameter. If you increase the circumference by two
    >> inches, the diameter increases by 0.64 inches (2/pi) whether you start
    >> with a circle 8 inches, 8 meters, or 8 miles in diameter.
    >>

    > Reminds me of the old brain teaser (not all that difficult):
    >
    > If a worm crawls round the equator and a bird flies 2 metres above the
    > worm, how much further has the bird travelled when they get back to
    > their starting point?
    >
    > Most people think it's thousands of miles...it's actually about 6.3 metres.


    I know I was surprised the first time I heard that.
     
  9. 41

    41 Guest

    Zog The Undeniable wrote:
    > If a worm crawls round the equator and a bird flies 2 metres above

    the
    > worm, how much further has the bird travelled when they get back to
    > their starting point?
    >
    > Most people think it's thousands of miles...it's actually about 6.3

    metres.

    C1-C2 = 2piR1-2piR2
    = 2pi(R1-R2) = 2pi(2m)
    = about 12.6mu
     
  10. A Muzi

    A Muzi Guest

    >> Zog The Undeniable wrote:
    >>If a worm crawls round the equator and a bird flies 2 metres above
    >> the
    >>worm, how much further has the bird travelled when they get back to
    >>their starting point?
    >>Most people think it's thousands of miles...it's actually about 6.3

    > metres.


    41 wrote:> C1-C2 = 2piR1-2piR2
    > = 2pi(R1-R2) = 2pi(2m)
    > = about 12.6mu


    What's a mu?
    I got 12.566 meters

    --
    Andrew Muzi
    www.yellowjersey.org
    Open every day since 1 April, 1971
     
  11. JeffWills

    JeffWills Guest

    A Muzi wrote:
    >
    > What's a mu?



    I dunno. What's mu with you?

    Jeff
     
  12. 41

    41 Guest

    A Muzi wrote:
    > >> Zog The Undeniable wrote:
    > >>If a worm crawls round the equator and a bird flies 2 metres above
    > >> the
    > >>worm, how much further has the bird travelled when they get back to
    > >>their starting point?
    > >>Most people think it's thou sands of miles...it's actually about

    6.3
    > > metres.

    >
    > 41 wrote:> C1-C2 = 2piR1-2piR2
    > > = 2pi(R1-R2) = 2pi(2m)
    > > = about 12.6mu

    >
    > What's a mu?
    > I got 12.566 meters


    For either perverse or sinister reasons, Google randomly puts an extra
    letter at the end of every one of my posts. This time, it was a 'u'.
    Also, randomly intersperses blanks throughout, if the message is long
    enough. Wonder what will happen to this one.

    o
     
  13. 41

    41 Guest

    JeffWills wrote:
    > A Muzi wrote:
    > >
    > > What's a mu?

    >
    >
    > I dunno. What's mu with you?


    Good one, but I think you meant, "Ah no know, what's-a-mu wid you?"e
     
  14. A Muzi

    A Muzi Guest

    >>>>Zog The Undeniable wrote:
    >>>>If a worm crawls round the equator and a bird flies 2 metres above
    >>>>the
    >>>>worm, how much further has the bird travelled when they get back to
    >>>>their starting point?
    >>>>Most people think it's thou sands of miles...it's actually about
    >>>> 6.3
    >>>>metres.


    >>>41 wrote:> C1-C2 = 2piR1-2piR2
    >>> = 2pi(R1-R2) = 2pi(2m)
    >>> = about 12.6mu


    >> A Muzi wrote:
    >>What's a mu?
    >>I got 12.566 meters


    >41 wrote:
    > For either perverse or sinister reasons, Google randomly puts an extra
    > letter at the end of every one of my posts. This time, it was a 'u'.
    > Also, randomly intersperses blanks throughout, if the message is long
    > enough. Wonder what will happen to this one.
    >
    > o


    I guess I was sort of saying "ditto".

    --
    Andrew Muzi
    www.yellowjersey.org
    Open every day since 1 April, 1971
     
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