Originally Posted by
cyccommute
Yes, installing a longer cage derailer is an option. A medium cage derailer will handle a 34 tooth cog. About $100 for the derailer and extra for the chain.
A less expensive alternative that
might work, is the
Wolf Tooth RoadLink. I used one to increase the capacity of an old XTR derailer so that I could use a 36 tooth low. I could probably put in a 40 but I’m already at a silly low gear. It’s only $21. It might or might not work but it’s a bit cheaper than the other route.
The Wolftooth will certainly increase the
max sprocket size capacity, by simply lowering the RD to provide more clearance. However, it won't increase the
chain wrap capacity, which may or may not be an issue with a larger (ie, wider-range) cassette. If the OP is currently using an 11/30 cassette and wants to go with an 11/34, his RD's cHain wrap capacity will have to increase by 4 teeth. Depending on his chainring setup and the capacity of his current RD, the Wolftooth might be all he needs to achieve this. Before buying anything, calculate the chain wrap of the proposed new drivetrain and determine if the current RD's chain wrap capacity can handle it (with some allowance for RDs generally exceeding official specs). If you're in the ballpark re chain wrap capacity, the Wolftooth alone will likely do the trick.