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Can I use a standard crankset on the front then the stoker has tandem specific cranks or is the eccentric bb usually wider?
The eccentric will be a normal 68mm wide on nearly every tandem ever built. Cranks will depend on what drive you use, crossover needs 3 tandem cranks and only the stoker's drive side is common with a solo, straight through can use 4 solo cranks among other benefits, but one of the drive side chainrings is used for the timing chain so you lose the use of that one as a final drive ring, unless you use John Allen's hack with the timing chain outside the final drive rings.
The tandem non-standards which can bite you are rear hubs, where there is no general agreement on OLN dimension, and headsets where you might come across a 1¼" threaded headset depending on the vintage of the frame you find.
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Usually for the front you have a crank with no ring on the right and a ring on the left. So you can't use a regular crankset, unless you use double sided pedals and are okay with them wanting to unscrew themselves.
Have a Google for stronglight impact tandem crankset. That's what we have and they do the job for not too much £££
I'm considering building up a tandem this summer. Other than the obvious (long chain, cables etc) what tandem standards are going to cause me issues?
Can I use a standard crankset on the front then the stoker has tandem specific cranks or is the eccentric bb usually wider?