Re: outer diameter of a 56 tooth chainwheel ?

[Zog The Undeniable]

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".

 

[JeffWills]

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

 

[Leo Lichtman]

"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.

 

[Zog The Undeniable]

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.

 

[A Muzi]

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

 

[Jim Smith]

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.

 

[Zog The Undeniable]

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.

 

[Jim Smith]

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.

 

[41]

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

 

[A Muzi]

>> 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

 

[JeffWills]

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


I dunno. What's mu with you?

Jeff

 

[41]

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

 

[41]

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

 

[A Muzi]

>>>>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