Bicycle Mechanics - Cassette swap straightforward?

The new bike that I've got my eye on is a compact double, 105 group, with a 12-25 cassette. However, I happen to have a new 105 12-27 cassette that might work better for me. If I have the shop swap this for me, would it be a simple swap or could there be chain length issues?

(It would be nice if it doesn't require a new (longer) chain since I'd still have the 12-25 and could go back to it at any time.)

There is a very small chance that your chain will be too short but the only way to tell is to try!
Swap the casette and see if there is enough chain to shift into the big chainring and big cog... if it goes in and comes out without binding then you are good to go!

Just so you know, the tools necessary to remove a cassette will only cost about $20 (assuming you already have an adjustable wrench) and it is a very simple operation. A shop will probably charge you $6 - $10 or so.

Thanks for the response! I do have the tools and have done this myself before. I just thought that the dealer might do it for free considering what I'm paying for the bike, and then it would be installed when they do their final tuning and checking out before I pick it up.

Thanks for the response! I do have the tools and have done this myself before. I just thought that the dealer might do it for free considering what I'm paying for the bike, and then it would be installed when they do their final tuning and checking out before I pick it up.

I'd think they would. This is a very minor/easy change.

- Mark

I'd think they would. This is a very minor/easy change.

- Mark

Even adding a link or two should chain be too short to accomodate the 27t cog would be easy.

Highly unlikely that you would need another link. But it is important the check the big to big combination as said above.

Be sure to measure the chain for stretch before changing cassettes.

Al