Specialised Sirrus Rear Cassette Change - What To Do and How To Do It

Hi All,

I've a trip coming up and I want to change my bike's road gear set-up
to something more mountain. The bike itself is a 2004 model
Specialised SIrrus A1. The current model has a Shimano HG50 8-speed
12-25t rear cassette. At the moment I can't be sure my model uses the
same, but, assuming it does, what would one need to purchase to allow
for more appropriate gearing. I'd like to do this simply and cheaply.

Many thanks.

Simon

On Mar 28, 7:09 pm, wrote:
Hi All,

I've a trip coming up and I want to change my bike's road gear set-up
to something more mountain. The bike itself is a 2004 model
Specialised SIrrus A1. The current model has a Shimano HG50 8-speed
12-25t rear cassette. At the moment I can't be sure my model uses the
same, but, assuming it does, what would one need to purchase to allow
for more appropriate gearing. I'd like to do this simply and cheaply.

Many thanks.

Simon

Here's how:
http://www.parktool.com/repair/readhowto.asp?id=48
The tools needed are quite cheap and will last forever.

All Shimano cassettes since 1990 are removed in the same fashion. If
you change to a wider-range cassette, bear in mind that you may need a
rear derailleur with a longer cage and almost certainly need to add a
couple links to the chain.

Jeff

wrote:
Hi All,

I've a trip coming up and I want to change my bike's road gear set-up
to something more mountain. The bike itself is a 2004 model
Specialised SIrrus A1. The current model has a Shimano HG50 8-speed
12-25t rear cassette. At the moment I can't be sure my model uses the
same, but, assuming it does, what would one need to purchase to allow
for more appropriate gearing. I'd like to do this simply and cheaply.

Many thanks.

Simon

I'm not sure what model you've got since A1 seems to be Specialized's
name for an aluminum alloy. The 2004 models can be found here -

http://www.specialized.com/bc/SBCBkM...4&sid=04Sirrus

The Sirius base model uses a Shimano Sora rear derailleur. The Sirrus
Sport and Elite use the Shimano Tiagra rear derailleur. The Sirrus Comp
and Pro models use 9 speed cassettes and so don't match your model.

You can find the technical specs on the Shimano derailleurs under the
"Technical Documents" left side menu choice at -

http://bike.shimano.com/publish/cont...l_service.html

Go to "Road Bike" and look under "Tiagra" or "Sora."

I wanted to do something similar but I found that I couldn't simply put
a cassette with a bigger big cog on. Using the big chain ring with a
bigger big sprocket (a no no in any case with a triple chain ring setup)
pulls the chain tighter than its length can handle and if a longer chain
is used then the rear derailleur with a short cage can't keep the chain
from getting too slack when the opposite extreme chain ring sprocket
combination is used.

The derailleur I had (a Tiagra GS - with a long cage) couldn't handle a
sprocket bigger than 27 teeth. This matches your situation as far as I
can tell. I had to get a different rear derailleur which I did when I
saw a sale at Nashbar for the Deore LX (M580-SGS). This model has an
extra extra long cage and can handle a sprocket with as many as 34T.
There are other factors involved such as the max differences between the
biggest and smallest sprockets and chain rings and also something called
"total capacity" which is a measure of both those factors.

The key though is the extra long cage for the rear derailler. The one
you've got can only handle 27 teeth as a max. Note also that a longer
chain will be needed.

There's also the difference in the way shifting is handled. Some
mountain bikes use something called "rapid rise" shifting where an easy
click shifts to the bigger cassette sprocket gear (easier pedaling).
This is opposite to a road bike where the easy click, rather than hand
twist, shifts to the smaller sprockets (tougher pedaling). Shimano calls
this "low normal return spring." The Deore LX matches the road bike
setup so it's fine.

The cost of the swap depends on the quality of the components you want
to get. You need a new derailleur, chain and cassette.

Changing the derailleur doesn't require special tools other than the hex
wrenches of the right size. There's also rethreading the cable and
putting a cap on the end to keep it from fraying. Adjusting the
derailleur is a bit tricky but it's explained in the tech docs I linked
to. It's not that difficult and good to know. Removing the cassette is
easy but it requires a special adapter tool to remove a lock ring along
with a wrench to turn the adapter. About $10 for the adapter. Oh. I
forgot. There's also the chain whip tool to hold the cassette while
turning the lock ring adapter. $15 or so. Replacing a chain requires a
chain tool, which is in the $15 range. I started to do my own bike work
so I got a tool set when Nashbar had a sale. You might want to do the
same rather than buy the tools individually.

That's pretty much it. Not worth it if you ask me unless you want to do
most of the regular bike maintenance work yourself, which I did. It's
much easier to clean a bike drive train if you remove the parts to clean
them.

You can try to find a cassette with a 27 tooth big sprocket and see if
that fits your needs. That would avoid the need for the derailleur and
chain (not sure about the chain). It might satisfy your needs.

On 29 Mar, 17:34, MkTm wrote:
wrote:
Hi All,

I've a trip coming up and I want to change my bike's road gear set-up
to something more mountain. The bike itself is a 2004 model
Specialised SIrrus A1. The current model has a Shimano HG50 8-speed
12-25t rear cassette. At the moment I can't be sure my model uses the
same, but, assuming it does, what would one need to purchase to allow
for more appropriate gearing. I'd like to do this simply and cheaply.

Many thanks.

Simon

I'm not sure what model you've got since A1 seems to be Specialized's
name for an aluminum alloy. The 2004 models can be found here -

http://www.specialized.com/bc/SBCBkM...4&sid=04Sirrus

The Sirius base model uses a Shimano Sora rear derailleur. The Sirrus
Sport and Elite use the Shimano Tiagra rear derailleur. The Sirrus Comp
and Pro models use 9 speed cassettes and so don't match your model.

You can find the technical specs on the Shimano derailleurs under the
"Technical Documents" left side menu choice at -

http://bike.shimano.com/publish/cont.../technical_ser...

Go to "Road Bike" and look under "Tiagra" or "Sora."

I wanted to do something similar but I found that I couldn't simply put
a cassette with a bigger big cog on. Using the big chain ring with a
bigger big sprocket (a no no in any case with a triple chain ring setup)
pulls the chain tighter than its length can handle and if a longer chain
is used then the rear derailleur with a short cage can't keep the chain
from getting too slack when the opposite extreme chain ring sprocket
combination is used.

The derailleur I had (a Tiagra GS - with a long cage) couldn't handle a
sprocket bigger than 27 teeth. This matches your situation as far as I
can tell. I had to get a different rear derailleur which I did when I
saw a sale at Nashbar for the Deore LX (M580-SGS). This model has an
extra extra long cage and can handle a sprocket with as many as 34T.
There are other factors involved such as the max differences between the
biggest and smallest sprockets and chain rings and also something called
"total capacity" which is a measure of both those factors.

The key though is the extra long cage for the rear derailler. The one
you've got can only handle 27 teeth as a max. Note also that a longer
chain will be needed.

There's also the difference in the way shifting is handled. Some
mountain bikes use something called "rapid rise" shifting where an easy
click shifts to the bigger cassette sprocket gear (easier pedaling).
This is opposite to a road bike where the easy click, rather than hand
twist, shifts to the smaller sprockets (tougher pedaling). Shimano calls
this "low normal return spring." The Deore LX matches the road bike
setup so it's fine.

The cost of the swap depends on the quality of the components you want
to get. You need a new derailleur, chain and cassette.

Changing the derailleur doesn't require special tools other than the hex
wrenches of the right size. There's also rethreading the cable and
putting a cap on the end to keep it from fraying. Adjusting the
derailleur is a bit tricky but it's explained in the tech docs I linked
to. It's not that difficult and good to know. Removing the cassette is
easy but it requires a special adapter tool to remove a lock ring along
with a wrench to turn the adapter. About $10 for the adapter. Oh. I
forgot. There's also the chain whip tool to hold the cassette while
turning the lock ring adapter. $15 or so. Replacing a chain requires a
chain tool, which is in the $15 range. I started to do my own bike work
so I got a tool set when Nashbar had a sale. You might want to do the
same rather than buy the tools individually.

That's pretty much it. Not worth it if you ask me unless you want to do
most of the regular bike maintenance work yourself, which I did. It's
much easier to clean a bike drive train if you remove the parts to clean
them.

You can try to find a cassette with a 27 tooth big sprocket and see if
that fits your needs. That would avoid the need for the derailleur and
chain (not sure about the chain). It might satisfy your needs.

Thank you for the advice - very useful!