[chriskaiser]

I am getting a crankset from FSA 42/53 chainrings one of the options that I have is • 170mm, 172.5mm, 175mm what does it mean? It will be for a bike with Campy parts.
Thanks FSA

 

[NJPhil]

The 170mm. 172.5mm or 175mm option is the crank arm length. If you are happy with your current cranks I would get the same length on the new cranks also.

 

[Nate at RIT]

Most bikes comes with 175, assuming you're somewhere near average height. It should be stamped on the cranks that are on the bike now.

 

[Carbon Fetish]

Most bikes comes with 175, assuming you're somewhere near average height. It should be stamped on the cranks that are on the bike now.

Most mountain bikes come with 175. Most road bikes come with 172.5. The length of your crank arms effectively changes the required torque per revolution, thus changes your gear ratios.