For me I go by rubbing sounds for the fd. If I hear slight rubbing in the big/big and/or small/small combination, it's probably getting close since you shouldn't be in those combinations with a triple. The idler on this thing is fairly loud and masks any rubbing sounds. I could just remove the idler instead I guess, it's just one bolt to get the pulley out.

Now where did my stokers go??? The wife is out tonight with friends and the kids are going to grandma's.