Originally Posted by
timdow
If you use an on the bike method, without running chain through rear derailleur, wrap chain around big ring and biggest cog, then add two links. I have not used mullet cassettes though.... I just read online that this method is only good for 36T and under.
If it is not exact, I personally err on the short side for the chain as I would never be in big ring big cog combo, or anywhere close to it. On the other hand, it is a lot easier to remove a link if the chain turns out to be too long than to add a link.
I would never shift into a big-big combo, either. Except that I have on multiple occasions. It's all too easy to lose concentration and shift into the big cog when you were sure you were in a small ring that turned out to be a big ring. Happens to me a couple times a year, when I'm tired, distracted, hot. Because I've sized for big-big, I've managed to avoid damaging anything when I do something stupid like that.