I've done my reading and am ready to loft my first set of plans, a 29er project. Before I put pencil to paper, and since it's my starting point, I want to exhaust all my resources; how do y'all determine your bottom bracket height? The radius of my wheel with the tire is 14 3/4 inches.
Honestly by looking at other designs I have experience with. I also look at BB height as a design issue. I look at similar bikes made by famous builders or companies and get a lot of data points. I figure out whether I was comfortable riding these bikes, I am overall quite tall but marginally short legged, so BB height is an issue for standover. I also look at technical factors like clearance and how the ride feel is affected. Then I just guess.
I did once try to measure the me on the bike tire deflected height of my tires and was surprised how little change there was, even given my weight.
I was wondering the same thing about 29ers, so I looked around at what the best 29er custom builders were dong. I found that most often they were doing 6-8cm of BB drop. I just finished one with a 7cm drop and 175mm cranks, the customer has taken on the roughest trails we have and had no pedal strike issues at all.