+1 on SKS Chainboard

specs are here:

http://www.sks-germany.com/?l=en&a=p...376fac5fe2b93d

note that the 199mm-sized version will handle between 46 and 48 teeth.

common in Germany and I hear great things about the durability of them.

cranks come off for installation as it's a very permanent solution that should last the lifetime of the bike.

this Excel file specifies which components are compatible with it.

http://www.sks-germany.com/download/...t_20131211.xls

good luck.