I am considering upgrading my old trekking bike from a 3x7 to a 3x9 drivetrain. The bike is currently equipped with a 26/36/46 Shimano Exage FC-M320 which I intend to keep due to its wide sprocket spread and relatively good condition (bottom bracket will be replaced). Front derailleur is a Suntour FD-XR15 which you cannot find very detailed information about, but should have a chain line of 47.5 mm.
As the upgraded bike should be used for touring, I would like to have a wider gear range, especially for the lower gears to make climbing steep passages with heavy load easier.
Since the rear wheel will be replaced, switching to a more modern drivetrain became an option and I fancy with a 11-34 9-speed cassette (e.g. Shimano CS-HG400-9) combined with an SRAM X5 rear derailleur (long cage version).
The maximum capacity of the 9-speed X5 rear derailleur is specified as 45 teeth (given in reseller 'fact sheet'). I calculated the required capacity as
(46-26) + (34-11) = 20 + 23 = 43
which seems to be within specification.
Can I keep the existing front derailleur and crankset? Will the chain line be affected by changing the cassette and rear derailleur resulting in compatibility issues which I missed? Do have to take care about the derailleur hanger?
Note: The existing Shimano shifters/triggers will also be replaced with SRAM X5 3x9 ones and all shifting cables will be swapped out.