Originally Posted by Artkansas
Assuming that you are trying to brake and signal in a street situation, traditionally you signal with the left hand. That leaves the right for braking. If you are going to jam on the brakes one-handed, you definitely want to be squeezing the rear brake as squeezing the front brake with only one hand on the handlebars is a sure fire way to crash. Hence, install the rear brake on the right.
The front brake carries 70%-80% of any vehicles's braking power. On a motorcycle, about the only time you need the rear brake is in loose conditions--sand, gravel, maybe wet (but not always)--and under full panic conditions, plus depending on circumstances, locking the back wheel can be just as nasty as locking the front. Because you can't see the rear wheel and most riders don't recognise the slide till it's too late, it's easy to lose control over-braking the rear.
On a bike, I see two things here: one, if your left hand is in the air signaling, by the time you get it to the lever you're deeper in trouble already because the rear isn't as effective. And in a full panic stop, I'd think you'd want your strongest and most sensitive hand already on your levers, modulating your strongest brake.
Personally I set my bikes up with front brake on right lever. In normal riding I rarely use my rear brake. If I'm expecting to need it, like when running stop signs, I'll make sure I'm on both levers.
JiO