cassette ratio

[knonist]

Hello, I'm thinking of purchaseing a spare cassette whilst it in on sale, and I dont know much about it. I guess it is time for me to learn.

My current drivechain config is:

Shifters: Shimano Deore, 9 speed
Front: DerailleurShimano Deore
Rear: DerailleurShimano 105
Crank: Shimano M443 Octalink 48/36/26
Cassette:SRAM PG950 11-26, 9 speed

and I'm thinking of purchaeing a SRAM PG970 Cassette (11-32)or (11-34), to replace the PG950 in the future as I guess it will need replaceing in the next 6-9 months as I do around 370 miles a month. I would like to know the following before I made the purchase.

1) what's the difference between 11-26 & 11-32 or 11-34? Would I feel the difference?
2) will it fit to my current config? Do I have to change my chain length to fit it?
3) it is better off to let the LBS to fit it or DIY isnt that difficult?


Thanks in advance

 

[Will1985]

The differences are lower gears and bigger jumps between gears in the middle and at the large end of the cassette.

If you haven't already, invest in a chainwhip and lockring removal tool - this is a simple procedure.

 

[accountantpete]

You will need a long cage rear mech and longer chain.

The difference is that there are even bigger gaps in the gears than you have at present - if you like a smooth transition through the gears when going uphill etc then you will notice - otherwise if you just select a gear and pedal then it wont be that important.

 

[PpPete]

My current drivechain config is:

Shifters: Shimano Deore, 9 speed
Front: DerailleurShimano Deore
Rear: DerailleurShimano 105
Crank: Shimano M443 Octalink 48/36/26
Cassette:SRAM PG950 11-26, 9 speed

105 is a road mech. Per Shimano it will not handle more than 27 teeth.
In practice it will just about handle 30T - but not 32T

If you want to run an 11-32 or 11-34 cassette than you'll need a Deore rear mech or one of similar capacity.

 

[knonist]

105 is a road mech. Per Shimano it will not handle more than 27 teeth.
In practice it will just about handle 30T - but not 32T

If you want to run an 11-32 or 11-34 cassette than you'll need a Deore rear mech or one of similar capacity.

so if i dont want to change the rear mech, then 11-26 is my maxium?

 

[RecordAceFromNew]

If your chainset goes down to 26 as you have indicated, I wonder if you really want to go lower than 28 or 30 at the back (with which as porkypete said you are unlikely to have to change your rear mech). Have you done a what-if assessment with this handy program by the late, great Sheldon?

Incidentally 105 rear mechs come in short, medium as well as long cage versions. Do you know which one you have? You might not need to change it at all even if you go up to 34 at the back.

 

[knonist]

If your chainset goes down to 26 as you have indicated, I wonder if you really want to go lower than 28 or 30 at the back (with which as porkypete said you are unlikely to have to change your rear mech). Have you done a what-if assessment with this handy program by the late, great Sheldon?

Incidentally 105 rear mechs come in short, medium as well as long cage versions. Do you know which one you have? You might not need to change it at all even if you go up to 34 at the back.

Thanks for your info, i dont even know how to fill in the inquestionaire.

In regard witht the rear mech, here is the info of it. I guess it is a long cage, but I'm not entirely sure.
here is more info of my bike, can someone confirm that for me? thanks

http://www.trekbikes.com/us/en/bikes/2008/archive/76fx

 

[RecordAceFromNew]

To be sure, can you measure the cage length of your rear mech per the top of the page here ?

 

[RecordAceFromNew]

Actually thinking about it you must have the long cage model, because your current setup has already used up the 105 long cage's official chain wrap capacity of (48-26)+(26-11), which is 37 teeth.

What that means, is that your rear mech can indeed handle a 11-34 cassette. You should be aware however because of the range of your chainset the rear mech might not be able to keep the chain in adequate tension if for whatever reason you ended up running the small "granny" front and the smaller back sprockets at the same time - but since there is no rational reason to do that, the scenario is avoidable.

You will need a new chain if you want to use the 11-32 or 11-34 because the existing chain will be too short (and probably worn anyway).

 

[PpPete]

AFAIK 105 mechs only come in Short (SS) and Medium Cage (GS)
SS has total capacity of 29T
GS has total capacity of 37T

You must have a GS model

so if i dont want to change the rear mech, then 11-26 is my maxium?

As you've used 22T of the total capacity on the front, in theory you can only have 15T difference between top & bottom of casette. In practice you'd have no trouble with a 11-27 cassette.

I doubt very much whether 11-32 cassette will work satisfactorily with a 105 mech. I've got a mech with same capacity and same tooth difference at front. I'm running a 12-30 cassette, but that requires careful handling, if I inadvertently get anywhere near big-big or small-small the whole thing locks up.

To run 11-32 cassette you'd need rear mech with a total capacity of at least 43T ... which means MTB gear like the Deore.... and those have a longer cage than the GS road mechs.

 

[threefingerjoe]

Actually, this is kind of a strange setup. Is it original on the bike? Generally speaking, (I try to avoid saying "always" or "never") a "standard" road bike has chainrings something like 52-39-30 and a cassette of 11-25 or 26. A mountain bike or hybrid has chainrings like you describe (48-36-26) but with an 11-32 or 34 cassette. A touring bike has roadbike chainrings with a mountain bike cassette. You seem to have a hybrid or mountain chainring set and a roadbike cassette.

As others have said, invest in a chainwhip and cassette tool, because you'll use it more than once. As someone else said, make sure that your rear derailure will accept a wide ratio cassette. I'm inclined to think that the cassette has been changed, from a wide ratio to a narrow (road) ratio, and if that is the case, it may still have the original rear mech (which would mean that it will accept a wide ratio cassette).

Keep us posted on this. I'm curious.

 

[knonist]

Actually, this is kind of a strange setup. Is it original on the bike? Generally speaking, (I try to avoid saying "always" or "never") a "standard" road bike has chainrings something like 52-39-30 and a cassette of 11-25 or 26. A mountain bike or hybrid has chainrings like you describe (48-36-26) but with an 11-32 or 34 cassette. A touring bike has roadbike chainrings with a mountain bike cassette. You seem to have a hybrid or mountain chainring set and a roadbike cassette.

As others have said, invest in a chainwhip and cassette tool, because you'll use it more than once. As someone else said, make sure that your rear derailure will accept a wide ratio cassette. I'm inclined to think that the cassette has been changed, from a wide ratio to a narrow (road) ratio, and if that is the case, it may still have the original rear mech (which would mean that it will accept a wide ratio cassette).

Keep us posted on this. I'm curious.

Thank you for the replies, the chainrings & cassette are origional and I think I will stick to my origional ratio in the future.
Is there much difference between a Shimano Tiagra Cassette and a SRAM PG950?
There are in the similar price range and I was told that the SRAM ones will last longer and feel better, is that true?