Re: Shimano 105 rear derailleur weird specs

[Grenouil]

"Rick Onanian" > wrote in message
...
>
> 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.

[G Huang]

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.

[Rick Onanian]

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

[Rick Onanian]

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

[Bruce]

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
...
>
> 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/componenttemplate.asp?partnumber=RD-5501-
> SS-S
> http://bike.shimano.com/Road/105/componenttemplate.asp?partnumber=RD-5501-
> GS-S
>
> Or, in tiny URLs:
> Double -- http://tinyurl.com/jilr
> Triple -- http://tinyurl.com/jilp
>
>
> --
> Rick Onanian

[Bruce]

"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.

[Qui si parla Campagnolo]

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

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
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