I have an old road bike that has a 12/25 cassette. I want to change this to a 11/30 cassette. I have a medium derailleur. Will this work?
-
3Maybe. Depends on all the other specs, like which exact derailleur, which front derailleur, which front chainrings, etc. Let us know.– John ZwinckCommented Aug 7, 2016 at 20:00
-
Derailleur have two key specs - Capacity which is the total difference front chairing size and rear cassette, and Maximum cog size. You may need a new derailleur to go to the larger cassette.– mattnzCommented Aug 7, 2016 at 21:11
-
If you post the exact part number of the medium derailleur we may be able to give you clear advice.– Rob ShepterCommented Aug 9, 2016 at 15:44
Add a comment
|
2 Answers
With an old road bike it's impossible to tell just by looking. Many older derailleurs were designed when 28T was as big as it got, but they will still work with a 30T. But they might not, too.
If you're definitely going to make the change there's no real loss if you buy the cassette and try it. If the derailleur doesn't work, buy a new one. You might pay two lots of shipping, in which case the question is whether the second lot of shipping is enough to make it worth buying the derailleur anyway.
A better option would be to see if you can scrounge parts from a local bike co-op or tip shop. That way the cost is mostly your time, and if something doesn't work it doesn't take long to find a different one. Even if you end up running an MTB derailleur, the main thing is that it works.
You may have unusable combinations.
For example, you might not be able to use the large front chainring with your new large 30 tooth cassette cog. This combo consumes more 5 chain links, and a medium rear der cage probably doesn't not have enough range to cough up 5 links.
But maybe you won't miss that combination. I'm guessing you'd use the new 30 in low gear situations- with a small front chain ring.
So will it work? Yes, with some qualifications. This is an old road bike- will be used as a beater on a college campus? Or, are you wanting to not spend much on it? If you can deal with the limitations, it should be ok.
