I have an xtr 9130 crank for a superboost chainline (56.5) I’d like to use on a new 55 chainline Santa Cruz (shorter 165 arms and narrower Q factor than the stock xt crank). Does the 1.5mm difference make a significant difference or are there other issues I’m not thinking of that would make this a terrible idea?
Does that crank use a flat, 0mm offset chainring? If so, you could get a Wolf Tooth chainring with 3mm offset. Yes, it would move the chainline to 53.5mm, but frankly the Shimano 12sp MTB drivetrain is more tolerant of a slightly inboard chainline than a slightly outboard one. The only concern then is if the chainring will clear the chainstay.
The other option is to shift the crankset 1.5mm to the left. Yes, this will offset your pedals too, but one would be surprised how often cranks are not symmetric. It’s possible you would actually be evening out the stance.
Appreciate it and good to know on inward tolerance. A little more searching and it looks like Wheels Manufacturing sells a 1.5mm inward offset ring that could do the trick as well.