Do you mean 11-34?
If it's a "road" bike, there's a good chance the Rder may not have the capacity to handle a 34T cog.
There are basically 2 issues-
Will the 34T actually fit, without the RDER rubbing it
and
Will the RDER have enough "chain wrap" capacity to handle the 23T difference of the rear cogs + the difference between the chain rings. You didn't say if you have a double or triple up front.