Buying a new cassette....a little help.....

Simon1890 Posts: 117
edited March 2009 in Road beginners
Hi guys,

I'm currently riding gearing of:
Compact at front (50/36)
12-25 9 speed tiagra cassette at back.

Using a Shimano 105 rear mech, tiagra front mech.

I want to change my cassette to an ultegra 12-27 cassette (i live around a lot of hills!!) but i'm unsure how to go about it. Is it just a case of buy the cassette and swap them or will i need a new chain or any other things i need to consider?

Also, regarding gearing, do certian gear combinations match others? (ie is a combination of 39 front, 28 rear the same as 36 front 25 rear?)



  • term1te
    term1te Posts: 1,462

    You'll almost certainly need a new chain, the teeth on the cassette and the chain wear/stretch together, so the nice new teeth may not mesh well with the old chain. You'll also need a couple of tools to get the old cassette off, a chain whip to stop the cassette turning whilst you undo the lock ring with a specific removal tool.

    I use a compact with at 12-27 cassette works a treat.
  • rally200
    rally200 Posts: 646
    27 should be fine - (its the max recommended for tigra rear mech -not sure about 105) I've got a 28 on mine with tiagra mech - it works though jockey wheel just about touches the cassette in botttom gear - even after adjust ingthe b-tension all the way (which puts the jockey wheels further away from the other cogs than is ideal )
  • John.T
    John.T Posts: 3,698
    Put your chainrings and cassette in here and you can see how gears compare. I prefer the 'gear inches' setting as I have been using these for years. It is easy to compare any sizes.
    39/28 is 37" and 36/25 is 38". Very close.