bottom bracket length(s)? / Chainline
I am building a tandem with a triple on the back. The frame has a 135mm rear spacing.
Standard road triple chainline is assumed to be 45mm, while MTB is 47.5-50mm. I will be using a 10 speed cassette (SRAM 110-28 OG1070).
If I want to set it up for optimum use of outer two chinrings and use the inner ring as the occasional bailout hillclimbing ring, then I am led to believe that I want to pull the chainling in a bit.
My plan is to use an old 118.5mm BB to mock up the spacing and then estimate the BB spindle length required to set the crankset up as close to the frame as possible cointingent upon achieving 45-47mm chainline.
Is this a reasonable approach?
Second question is twofold.
1. what length BB spindle? (assuming no data from the above experiment)
2. what are the arguments to run the same BB upfront, or two use a narrower one to aid Q factor versus ideal chainline for timing chain.
many thanks for your help,