Shimano 105 rear derailleur weird specs

[Rick Onanian]

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

 

[Grenouil]

"Rick Onanian" <[email protected]> wrote in message news[email protected]...
>
> 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 <[email protected]> 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 <gang@removethis_bell-labs.com> 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)
16.4%
17.4%
18.5%
19.%
20.3%
21.3%
22.5%

-Bruce

"Rick Onanian" <[email protected]> wrote in message news[email protected]...
>
> 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

 

[Malcolm Stewart]

"Bruce" <[email protected]> wrote in message news:[email protected]...
> 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.%
> 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

 

[Bruce]

"Malcolm Stewart" <[email protected]> wrote in message
news:[email protected]...
> "Bruce" <[email protected]> wrote in message news:[email protected]...
..... 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.%
> > 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?
R: The beauty of symmetry:

18/20 = 9/10 = 0.90 = -10% change
19/18 = 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.

 

[John Forrest To]

"Rick Onanian" <[email protected]> wrote in message news[email protected]...
> On Sat, 9 Aug 2003 17:06:15 -0500, Grenouil
<[email protected]>
> 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?

Don't risk it -- one day you may forget and have a serious problem.

If the setup you desire is close to the capacity of your current derailleur, then I think you should
set the bike up with a triple, a sufficiently long chain to handle the biggest cog and biggest ring,
and the current derailleur, and just see how it works. If the chain is way too slack in the smallest
cog/ring combo you would frequently use (this might not be the smallest cog and smallest ring -- if
you go into the gear combo by accident it's not a big problem), then get the new derailleur. If the
current rear derailleur can handle things, great, you saved some money.

JT

--
*******************************************
NB: reply-to address is munged

Visit http://www.jt10000.com
*******************************************

 

[Qui Si Parla Ca]

spamsink-<< 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. >><BR><BR>

BB, crank and front der and a little 'imaginative' chain length, meaning perhaps a little short...

<< How about, instead of a triple, compatibility with a mountain bike rear derailleur and then I use
a really wide ratio cassette? >><BR><BR>

yep, can use to about a 30t..for bigger, you really need a long cage rear der-like 105 or Deore..

<< I'd rather have the triple, but are Shimano road shifters compatible with Shimano MTB rear
derailleurs? >><BR><BR>

yep....

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

 

[Qui Si Parla Ca]

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
(303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene"