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Shimano 105 rear derailleur weird specs



 
 
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  #1  
Old August 9th 03, 11:06 PM
Grenouil
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Default Shimano 105 rear derailleur weird specs

"Rick Onanian" wrote in message
news

I'm looking at Shimano's website, considering a triple
crankset for my 2001 Giant TCR2, stock all 105 double.

I'm trying to figure out how little I can get away with
changing to put a triple on here.

I can see that I'll need [obviously] a crankset and a
front derailleur, but I wonder if I can get away with
no new rear derailleur.

How about, instead of a triple, compatibility with a
mountain bike rear derailleur and then I use a really
wide ratio cassette? I'd rather have the triple, but
are Shimano road shifters compatible with Shimano
MTB rear derailleurs?

I think I don't understand a few terms. Here's what the
site says about 105 double and triple rear derailleurs:

Rear derailleur for double cranksets:
Total Capacity: 37t
Front Difference: 22t

Rear derailleur for triple cranksets:
Total Capacity: 29t
Front Difference: 14t

Maybe I don't understand the terminology, but I figured
that the capacity is the amount of chain slack that the
derailleur can take up, and the front difference is the
largest difference in chainring that the rear derailleur
can swallow suddenly (though I'm sure I'm wrong about
that, I think I'm right about capacity).


Rick - read the 'oracle' - Sheldon Brown's site at
http://www.sheldonbrown.com/harris/index.html
The glossary and articles will provide all the information
you're looking for....

You can use a double RDR with a triple crank, but depending
on how you size the chain you could have some slack when
using the smallest ring and some of the smaller rear
sprockets, or a nasty experience when you inadvertently try
to use the largest ring and the largest sprocket if the
chain is too short. Probably better to get a triple RDR.

An alternative to a triple is to use a 'wider' cassette
and/or smaller chainrings. The largest rear sprocket for
most 'road' dérailleurs according to the Shimano spec is
27T, but lots of people report using 30 or even 32 - the
disadvantage is bigger gaps between adjacent sprockets.

The smallest chainring you can use on a 130mm BCD crank like
the Shimano 105 is 38T, so to go smaller you'll need a new
double crank with a smaller BCD.



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  #2  
Old August 9th 03, 11:09 PM
G Huang
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Default Shimano 105 rear derailleur weird specs

Rick Onanian wrote:

I think I don't understand a few terms. Here's what the
site says about 105 double and triple rear derailleurs:
...


If you download the service instruction in pdf on the same page, you'll
see that it all makes sense. The web page erroneously swapped the
numbers between SS and GS.

  #3  
Old August 9th 03, 11:32 PM
Rick Onanian
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Default Shimano 105 rear derailleur weird specs

On Sat, 9 Aug 2003 17:06:15 -0500, Grenouil
wrote:
Rick - read the 'oracle' - Sheldon Brown's site at
http://www.sheldonbrown.com/harris/index.html


Of course...I never thought to look there for
routine info, just the wacky stuff!

You can use a double RDR with a triple crank, but depending
on how you size the chain you could have some slack when
using the smallest ring and some of the smaller rear
sprockets, or a nasty experience when you inadvertently try
to use the largest ring and the largest sprocket if the
chain is too short. Probably better to get a triple RDR.


I think I can shift carefully. Do I dare find out?

An alternative to a triple is to use a 'wider' cassette
and/or smaller chainrings. The largest rear sprocket for
most 'road' dérailleurs according to the Shimano spec is
27T, but lots of people report using 30 or even 32 - the
disadvantage is bigger gaps between adjacent sprockets.


I can handle the wide ratios. I don't need 9 gears all
a single tooth (or two) apart from eachother.

The smallest chainring you can use on a 130mm BCD crank like
the Shimano 105 is 38T, so to go smaller you'll need a new
double crank with a smaller BCD.


Hmm...I could put a wider cassette and a new double
crankset with a smaller small ring...that may be an
option.

--
Rick Onanian
  #4  
Old August 9th 03, 11:33 PM
Rick Onanian
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Default Shimano 105 rear derailleur weird specs

On Sat, 09 Aug 2003 18:09:24 -0400, G Huang
wrote:
see that it all makes sense. The web page erroneously swapped the numbers
between SS and GS.


I was afraid that was the case.

--
Rick Onanian
  #5  
Old August 10th 03, 10:06 AM
Bruce
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Default Shimano 105 rear derailleur weird specs

Triple crank & BB, triple front der.... You will also need a new left
brifter to shift the triple.

If a wider cluster might fit your needs you can use a 12-27 with the stock
105, and maybe up to a 30. Or just switch the rear derailer to a MTBike (XT
or LX or ...) and use a 12-34. That's what I do with my Dura-Ace setup when
I want to tour with some extra baggage. I use a 12-34 w/ a 50-38, and only
switch the rear derailer. The 12-34 has very even ratios of 10 to 15%.
12-14-16-18-20-23-26-30-34

15.4% = ln(14/12)
13.4%
11.4%
10.5%
14.0%
12.3%
14.3%
12.5%

-Bruce



"Rick Onanian" wrote in message
news

I'm looking at Shimano's website, considering a triple
crankset for my 2001 Giant TCR2, stock all 105 double.

I'm trying to figure out how little I can get away with
changing to put a triple on here.

I can see that I'll need [obviously] a crankset and a
front derailleur, but I wonder if I can get away with
no new rear derailleur.

How about, instead of a triple, compatibility with a
mountain bike rear derailleur and then I use a really
wide ratio cassette? I'd rather have the triple, but
are Shimano road shifters compatible with Shimano
MTB rear derailleurs?

I think I don't understand a few terms. Here's what the
site says about 105 double and triple rear derailleurs:

Rear derailleur for double cranksets:
Total Capacity: 37t
Front Difference: 22t

Rear derailleur for triple cranksets:
Total Capacity: 29t
Front Difference: 14t

Maybe I don't understand the terminology, but I figured
that the capacity is the amount of chain slack that the
derailleur can take up, and the front difference is the
largest difference in chainring that the rear derailleur
can swallow suddenly (though I'm sure I'm wrong about
that, I think I'm right about capacity).

Everything else is the same (except the one for triples
weighs a few more grams).
Info from:
http://bike.shimano.com/Road/105/com...umber=RD-5501-
SS-S
http://bike.shimano.com/Road/105/com...umber=RD-5501-
GS-S

Or, in tiny URLs:
Double -- http://tinyurl.com/jilr
Triple -- http://tinyurl.com/jilp


--
Rick Onanian



  #6  
Old August 10th 03, 12:23 PM
Bruce
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Default Shimano 105 rear derailleur weird specs


"Malcolm Stewart" wrote in
message ...
"Bruce" wrote in message
...

...... The 12-34 has very even ratios of 10 to 15%.
12-14-16-18-20-23-26-30-34

15.4% = ln(14/12)
13.4%
11.4%
10.5%
14.0%
12.3%
14.3%
12.5%

-Bruce


I'm new to this. Why the need to use natural logs in the above

calculation?
What's wrong with simple ratios between adjacent pairs?

Cheers
--
M Stewart
Milton Keynes, UK
www.megalith.freeserve.co.uk/oddimage.htm




Q: Why the need to use natural logs in the above calculation?
A: The beauty of symmetry:

18/20 = 9/10 = 0.90 = -10% change
20/18 = 10/9 = 1.111 = 11.1% change.
ln(20/18) = minus ln(18/20) = 0.10536 = 10.5%

While I can do the first two calculations w/o computer assitance (and hence
while riding) I perfer the symmetric choice. That way when I downshift from
the 18 to the 20 it's the same change as when I upshift from the 20 to the
18.

Note the key word here is 'prefer'. Choose which method you prefer.

-Bruce
pure mathematician since age 7.


  #7  
Old August 10th 03, 02:14 PM
Qui si parla Campagnolo
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Default Shimano 105 rear derailleur weird specs

bruce- Triple crank & BB, triple front der.... You will also need a new left
brifter to shift the triple. BRBR

If the setup is 9s...the left shifter is double and triple compatible..think in
2001 it was...

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"
 




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