"Gearing" up for the Mountains!

[TxDoc]

Since you already have a compact AND a 12-25, I'd say you would be fine on most mountains. If you are going up really steep mountain passes, then you may consider going up to 26 or even 28 - but with a compact crankset you are very unlikely to need it.

[Pedal Wench]

Since you already have a compact AND a 12-25, I'd say you would be fine on most mountains. If you are going up really steep mountain passes, then you may consider going up to 26 or even 28 - but with a compact crankset you are very unlikely to need it.

I think it really depends on the individual rider, her knees, and where she's riding. My knees really do need a larger cassette - and I have a 34 small chainring. I use a 13-29 (campy) on my bikes that I use in hilly areas and mountains (Colorado). In Florida, my bikes with a standard double with a 12-25 is fine.

[jusdooit]

I am going to make a similiar change from 11-25 to 11-28. You should definitely replace the chain at the same time. The RD depends on compatibility, it has to be able to to carry the chain to the slightly larger cog.

To calculate the ratios, you simply divide the front by the rear. For instances 36/25 = 1.44. If you change only the rear cassette 36/28 = 1.29. The closer you are to 1.0 the easier it will be to pedal. If you only change the front to a34, then 34/25 = 1.36. If you change both then 34/28 = 1.21.

Good luck!!!