Depends on your budget. But get the same axle length as you have at the moment I guess. Unless your chainline is awful in which case a shorter axle will bring the chainring closer to the frame or vice versa (provided the cranks don't start rubbing on the shell or stays).
Depends on your budget. But get the same axle length as you have at the moment I guess. Unless your chainline is awful in which case a shorter axle will bring the chainring closer to the frame or vice versa (provided the cranks don't start rubbing on the shell or stays).