Originally Posted by
oldbobcat
My rule of thumb for tuning and using triples is to be able to work the entire rear cluster from the middle front ring.
I think this is a great approach, and one I use myself.
Most of my bikes are 3x7/8/9, most are flat bar index-shifted, most can use all combinations without rub, all can use reasonable combinations without rub. For fun (and learning, ODC, etc.), I do enjoy trying to tune the drivetrains so that you don't have any rub, ever, regardless of ill-advised gear selection. This is possible on some bikes and I have most of mine there...but it doesn't seem possible on a few of them.
One trick is to use an externally narrower chain than intended. For example, use a 9-speed chain on a 6/7/8-speed drivetrain. You can sometimes escape the rub in certain combinations. Of course, a counterbalance to that is some gear changes (especially front indexed gear changes) can be more sluggish.