Originally Posted by
Homebrew01
I measure by threading through the derailleur while in big-big. Seems like the easiest "no fail" way to me. You can be sure it works with your components.
What's the downside ?
Depending on the RD and the amount of cage tension, it sometimes takes three hands to do it this way and truly get to the shortest allowable chain (those long cage MTB RDs put a healthy amount of tension on the chain when fully extended). Big-big+1
should get you the exact same length (the +1" is allowance for the RD pulley routing) it's just a little easier to do since you're not trying to hold tension on a freshly lubed chain while you measure.