Hi, I'm right handed and play with a two-handed backhand. Which arm is supposed to supply most of the power with this shot, my right arm or left? So far I've been using my right arm mostly, and I've kinda noticed that I don't always get as much pace on my shots, but whenever I try using my left arm I always mess up the shot and can't get it to work. Also,does anyone know what kind of grip Andy Roddick used on his two-handed backhand? I've been using a continental grip on my bottom hand and semi-western on top.
Sorry this is late, but...
The general consensus is that the left arm should do more of the work. You should feel the ball more with your left arm, and use the right to help you stabilize the shot and guide the ball - it's there to assist.
There are some deviant accounts though, most famously from Andre Agassi, who advocates using the right arm. These are very few and far in between.
I'm not sure why you're interested in Roddick's backhand, as he's not exactly known for the shot (though his is better than people credit him for, and his issues are not grip-related, per se), but I'm pretty sure he uses right-hand continental.
The typical grip combinations are either top-hand Eastern / bottom-hand Continental, or a double Eastern ("two-fisted backhand").