Hi all,

I'd like to get a double crankset to replace a triple. Currently i have a 9 speed cassete and a tiagra front derailleur. What type of new derailleur do i have to get to work with the new crankset? Also, how can i tell what size bottom bracket is needed?

This is all the information i have about my bike (mercier aquila AL from bd):
Front derailleur: Shimano 3300 Triple front
Crank: FSA / RPM Forged Triple 52/42/30 T
Cassette: Shimano 9 Speed 12-25 T

Thanks in advance!