Originally Posted by
tsappenfield
I plan on changing the setup on my road bike from a triple chain ring to a compact double chain ring. If it’s relevant, the current triple chain ring setup is a Shimano 105. Will it be necessary to install a shorter axle and/or an all new bottom bracket to make this change?
Rsapp
tsappenfield,
I have just changed from a triple to a Shimano compact double 50~34T. YES, I had to change the BB. Reason was that my chain line was way to far outboard. Measurement from center seat tube was 57mm and a road bike should be close to 43mm.
Go to the Shimano site, select your type bike, type in your crankset, scroll down the table and it will give you the axle length for proper BB chain ring spacing.
2017-2018 SHIMANO Product Information Web
I needed a UN-55 110mm BB. I Amazoned it, installed it, and my chainring spacing is spot on 43.5mm and my drive chain runs good in all rear cogs.