Originally Posted by BabyCowHK

Birdy City (9SP STD) and Classic came with a square taper crankset which is not suitable for direct double chainring upgrade. Birdy Touring, 10SP Sport, GT and Rohloff have a wider chainline is because it's using the hollow crankset that provides a wider chainline. Many of my friends including myself have been using our hollow crank Birdys to do double chainring setup. That's the cheapest way to get a double chainring setup on Birdys.

The chain will scratch the rear fork when we use the square taper crank to do double chainring setup.

Also, Birdy with these BSA BB usually have 1x2mm spacer installed on the non-drive side and 2x2mm spacers on the drive side. That provides enough space for the 2nd smaller chainring t be installed. Funny enough the expensive Ti 2019 didn't have a single piece of spacer installed on the BB. That causes the chain to rub against the FD on Front-Small plus Rear-Large combination. I have no idea what was Pacific Cycles thinking in making such a low level mistake on a premium bike, or is it that they are taking customers for granted because we all paid to pre-order the bike?