"Gearing" up for the Mountains!

[OakLeaf]

Just to clear up:

Chainrings are the cogs in the front. You can buy and change those individually.

Cassette is the collection of cogs and spacers in the rear. For Shimano cassettes (and I think it's the same with other brands), the larger 3-4 cogs are one piece, and the smaller ones are loose. So you can change the smaller cogs (taller gears) individually, BUT they're not sold individually, so you would have to find a shop or a friend you could swap with, if you wanted custom gearing. Also, not all cogs can necessarily go in all positions on a given cassette.

Going from a 25T rear to 27 makes a huge difference to me on the steeper hills.

Do check your derailleur compatibility, although I think any cage that can accommodate 25T will handle 28? You'll probably need to adjust your B-screw if you make this change.


Also, I haven't noticed any ill effects or increased wear from using the same chain length with both. Technically I should probably be using one more link with the 27 than with the 25, but my long cage derailleur is big enough to accommodate it. If I were going to make a permanent change, or swapping back and forth with a larger gear difference (as I plan to replace my 11-25 with an 11-23 as soon as it wears out), then I would/will have to use two different chains as well. How badly you need to change your chain length probably depends on your chainstay length and derailleur cage size. Park Tool has a couple of methods for determining chain length.

If you're making a permanent gearing change but decide that you can keep your old chain until it wears out, then don't forget to make your new chain longer when you do replace it. If it were me, I'd put a note on my chain tool so I wouldn't forget.