# XT cassette (12-34) with 105 derailleur (long)

Status
Not open for further replies.
J

#### Jason Hodges

##### Guest
Has anyone had any luck with this? I looking for some lower gears on my commuter (Specialized
Sirrus). Appreciate any feedback.

Quoted from Shimano's european website: (105 rear derailleur capacity is 37 teeth) // How to
calculate the front difference, rear difference and total capacity of your shifting system. Each
front and rear derailleur has its limitations to the number of teeth that can be shifted. Mixing
components and not obeying this "rule" may lead to improper shift [function]. In order to make the
right choice of components please find below a sample calculation of front and rear difference and
total capacity:

Take for example a bike with a front gear ratio of 42/32/22 teeth and a cassette ratio of 11 - 28
teeth. To calculate the front difference you have to take the number of teeth of the biggest
chainring minus the number of teeth of the smallest chainring. So calculation for front difference
will be 42 minus 22 is 20 teeth.

To calculate the rear difference you basically do the same: You take the number of teeth of the
biggest sprocket of the cassette minus the number of teeth of the smallest sprocket. So calculation
for rear difference will be 28 minus 11 is 17 teeth .

To calculate the total capacity of the system we take above values: Front difference (20) plus rear
difference (17) is 37 teeth. An indication of the capacity of your system is mentioned in the
service instructions that can be found on this website. As mentioned before, components that are
mixed and are outside the total capacity may lead to improper shifting, either front, rear or both.

//

Max Quoted from Shimano's european website:
> (105 rear derailleur capacity is 37 teeth) // How to calculate the front difference, rear
> difference and total capacity of your shifting system. Each front and rear derailleur has its
> limitations to the number of teeth that can be shifted. Mixing components and not obeying this
> "rule" may lead to improper shift [function]. In order to make the right choice of components
> please find below a sample calculation of front and rear difference and total capacity:
>
> Take for example a bike with a front gear ratio of 42/32/22 teeth and a cassette ratio of 11 - 28
> teeth. To calculate the front difference you have to take the number of teeth of the biggest
> chainring minus the number of teeth of the smallest chainring. So calculation for front difference
> will be 42 minus 22 is 20 teeth.
>
> To calculate the rear difference you basically do the same: You take the number of teeth of the
> biggest sprocket of the cassette minus the number of teeth of the smallest sprocket. So
> calculation for rear difference will be 28 minus 11 is 17 teeth .
>
> To calculate the total capacity of the system we take above values: Front difference (20) plus
> rear difference (17) is 37 teeth. An indication of the capacity of your system is mentioned in
> the service instructions that can be found on this website. As mentioned before, components that
> are mixed and are outside the total capacity may lead to improper shifting, either front, rear
> or both.

That is the Official Party Line. Here's some more accurate info from my Bicycle Glossary:

"Capacity (of a derailer) "The "capacity" of a particular derailer model is the largest range of
sprocket sizes it can handle:

"For front derailers, when the derailer is mounted high enough to clear the largest chainwheel,
there is a certain minimum size that you need for the smallest ring so that the chain won't be
dragging over the bottom of the front cages. Different front derailers have different
capacities depending on how tall their cages are. It is expressed in a number of teeth, which
is the difference between the largest and smallest chainwheel. For instance, a 52/42/30 crank
set would call for a front derailer with a minimum 22 tooth (52-30) capacity.

"Front derailers are also designed to be used with a certain size for the largest chain ring.
The curvature of the outer cage plate is matched to this size. If you use a different size big
ring, capacity may be reduced. If the big ring is substantially smaller than the derailer is
designed for, shifting precision will suffer. If the big ring is much smaller than the derailer
is designed for, it may shift OK, but you are likely to have to "trim" the front derailer as
you shift the rear derailer to the extremes.

"For rear derailers, the capacity relates to the amount of chain slack the derailer can take
up, and is equal to the front range (22 in the example above) plus the rear range. Thus, if you
have a 52/42/30 crank set, and a 12-28 (16 tooth difference) cluster, the total capacity
required would theoretically be 38 teeth (22 front difference + 16 rear difference).

"Rear derailers are also commonly designed for a particular maximum size rear sprocket. If you
exceed this size, by too much, the jockey pulley may rub against the sprocket when using the
lowest gear.

"Manufacturers specify this fairly conservatively. They must do so, because they have to assume
that some of their derailers will be sold to incompetent cyclists, who will abuse their drive
trains by using the smallest chainwheel with the smaller rear sprockets.

"Competent riders can considerably exceed the official rated capacity, since they will not
misuse the granny ring by running it with the smaller rear sprockets, so it doesn't matter if
the chain hangs slack in those gears."

That said, in my experience, Shimano's "road" rear derailers generally work OK for a cassette with a
30 tooth cog, maybe for a 32, not for a 34.

I have a fair amount of experience with this, 'cause I sell a lot of custom wide-range touring
cassettes, such as 13-30 and 13-34.

See: http://sheldonbrown.com/harris/k7.html#9

Sheldon "Century Special" Brown +---------------------------------------------+
| Television: | A medium. So called because it is | neither rare nor well done. | --Ernie
| Kovacs |
+---------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

I have had success with an Ultegra long cage rear derailleur and a 12-32 coupled with a 39-53 front.
It is an inexpensive quick change conversion for a double road bike. Screw it on for a trip to the
mountains. Pop it off when you get home. Much simpler than dealing with a triple. I believe the 105
long has the same specs. Bill Brannon Please remove the nospam stuff to reply

"Sheldon Brown" <[email protected]> wrote in message
news:[email protected]...
> Max Quoted from Shimano's european website:
> > (105 rear derailleur capacity is 37 teeth) // How to calculate the front difference, rear
> > difference and total
capacity of
> > your shifting system. Each front and rear derailleur has its limitations to the number of
teeth
> > that can be shifted. Mixing components and not obeying this "rule" may
> > to improper shift [function]. In order to make the right choice of components please find below
> > a sample calculation of front and rear difference and total capacity:
> >
> > Take for example a bike with a front gear ratio of 42/32/22 teeth and a cassette ratio of 11 -
> > 28 teeth. To calculate the front difference you
have
> > to take the number of teeth of the biggest chainring minus the number of teeth of the smallest
> > chainring. So calculation for front difference
will be
> > 42 minus 22 is 20 teeth.
> >
> > To calculate the rear difference you basically do the same: You take the number of teeth of the
> > biggest sprocket of the cassette
minus
> > the number of teeth of the smallest sprocket. So calculation for rear difference will be 28
> > minus 11 is 17 teeth .
> >
> > To calculate the total capacity of the system we take above values: Front difference (20) plus
> > rear difference (17) is 37 teeth. An indication of the capacity of your system is mentioned in
> > the service instructions that can be found on this website. As mentioned before, components that
> > are mixed and are outside the total capacity may lead to improper shifting, either front, rear
> > or both.
>
> That is the Official Party Line. Here's some more accurate info from my Bicycle Glossary:
>
> "Capacity (of a derailer) "The "capacity" of a particular derailer model is the largest range of
> sprocket sizes it can handle:
>
> "For front derailers, when the derailer is mounted high enough to clear the largest
> chainwheel, there is a certain minimum size that you need for the smallest ring so that the
> chain won't be dragging over the bottom of the front cages. Different front derailers have
> different capacities depending on how tall their cages are. It is expressed in a number of
> teeth, which is the difference between the largest and smallest chainwheel. For instance, a
> 52/42/30 crank set would call for a front derailer with a minimum 22 tooth (52-30) capacity.
>
> "Front derailers are also designed to be used with a certain size for the largest chain ring.
> The curvature of the outer cage plate is matched to this size. If you use a different size
> big ring, capacity may be reduced. If the big ring is substantially smaller than the derailer
> is designed for, shifting precision will suffer. If the big ring is much smaller than the
> derailer is designed for, it may shift OK, but you are likely to have to "trim" the front
> derailer as you shift the rear derailer to the extremes.
>
> "For rear derailers, the capacity relates to the amount of chain slack the derailer can take
> up, and is equal to the front range (22 in the example above) plus the rear range. Thus, if
> you have a 52/42/30 crank set, and a 12-28 (16 tooth difference) cluster, the total capacity
> required would theoretically be 38 teeth (22 front difference + 16 rear difference).
>
> "Rear derailers are also commonly designed for a particular maximum size rear sprocket. If
> you exceed this size, by too much, the jockey pulley may rub against the sprocket when using
> the lowest gear.
>
> "Manufacturers specify this fairly conservatively. They must do so, because they have to
> assume that some of their derailers will be sold to incompetent cyclists, who will abuse
> their drive trains by using the smallest chainwheel with the smaller rear sprockets.
>
> "Competent riders can considerably exceed the official rated capacity, since they will not
> misuse the granny ring by running it with the smaller rear sprockets, so it doesn't matter
> if the chain hangs slack in those gears."
>
> That said, in my experience, Shimano's "road" rear derailers generally work OK for a cassette with
> a 30 tooth cog, maybe for a 32, not for a 34.
>
> I have a fair amount of experience with this, 'cause I sell a lot of custom wide-range touring
> cassettes, such as 13-30 and 13-34.
>
> See: http://sheldonbrown.com/harris/k7.html#9
>
> Sheldon "Century Special" Brown +---------------------------------------------+
> | Television: | A medium. So called because it is | neither rare nor well done. | --Ernie
> | Kovacs |
> +---------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
> 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
> http://captainbike.com http://sheldonbrown.com

Status
Not open for further replies.

Replies
1
Views
684
G
Replies
13
Views
1K
D
J
Replies
2
Views
913
R
Replies
7
Views
3K
S
Replies
1
Views
310
J
W
Replies
1
Views
404
B
Replies
3
Views
2K
M
Replies
3
Views
385
UK and Europe
Alex Butcher
A
F
Replies
2
Views
341
N