Dumb cassette question

nellie72

Hi all

I recently treated by self to a set of Shimano RS80's & used the existing 12-25 cassette from the old wheels when putting these on. I have now just invested in a turbo trainer (due to the English "summer") and thought i might buy a new Ultegra cassette for the RS80's, then put my existing cassette on my old rear wheel along with an indoor training tyre, so that they can be swapped out nice and quickly.

So my question is, if a buy a new cassette does it have to be the same gearing as I currently have or will I be able to buy, say an 11-28, and interchange the two without the need to make adjustments to my derailleur?

Hope this all makes sense!
Thanks in advance.

Monty Dog

If you fit a cassette with a larger bottom sprocket, then you may need to fit an extra link into the chain, or just make sure you never shift into the big sprockets when in the big chainring (not adviseable anyway due to sideload on chain). You may also need to adjust the B screw on your rear mech.

antonyfromoz

I did the same thing - had a 12-25 cassette on my original wheels and i have a 12-27 on the new ones. I use the original rear for the turbo and have fitted it with the correct tyre. I had a new chain fitted for another reason and had it measured for the 12-27 cassette but i am not sure if this was necessary. I didn't need to make any changes to the rear mech and now i can swap between wheels with no problems. HTH

P_Tucker

nellie72 wrote:

Hi all

I recently treated by self to a set of Shimano RS80's & used the existing 12-25 cassette from the old wheels when putting these on. I have now just invested in a turbo trainer (due to the English "summer") and thought i might buy a new Ultegra cassette for the RS80's, then put my existing cassette on my old rear wheel along with an indoor training tyre, so that they can be swapped out nice and quickly.

So my question is, if a buy a new cassette does it have to be the same gearing as I currently have or will I be able to buy, say an 11-28, and interchange the two without the need to make adjustments to my derailleur?

Hope this all makes sense!
Thanks in advance.

No adjustments to derailleur, but as has been mentioned if your chain was measured "as short as possible" rather than "as long as possible" then you'll have problems. Hopefully the people who put your bike together weren't morons.

cycleclinic

You size a chain for the cassette you are using not for a cassette that might go on in furture. The length should be wrap chain around big-big + 1 extra inch for standared sized jockey wheels.