What is the typical Q-factor like on 3-piece BMX cranks like Profiles or Flys? I've heard they are wide, but I haven't been able to find any numbers.

I'm shopping for the front cranks on a tandem build; I want long cranks -- 180 or 185mm, and in that range BMX cranks are one of the only options that doesn't cost your firstborn child. However, I know from my MTB that q of 170mm or wider is going to hurt my knees.

I've also heard you can cut down the spindle on some cranks, how narrow can you go? If I go with LHD crank up front I can also run a very narrow chainline for the sync chain.