If you are in the market for a mountain bike, and unsure of which type of frame to buy, get an aluminum frame, not one made of chro-moly. GT has made a whole line of both aluminum and chro-moly frames. The better line of bikes are made of aluminum and the lower end are made of chro-moly, which tells you that aluminum is better.

Aluminum is a lighter, more durable, and less forgiving frame, which makes the bike easier to handle. Chro-moly is heavier and weaker than aluminum, which makes it harder to control. Most aluminum frames are thicker than the chro-moly, which makes them stronger. Although the aluminum frame is bigger, it still weighs less than the chro-moly frame. The aluminum frame is less forgiving, which means that the ride is little bumpier, but it gives you a truer sense of the trail. And if you are planning to buy shocks, it won't matter if your bike is forgiving or not. In mountain biking, the lighter the bike, the better, so go with aluminum.

I have ridden both types of frames, so I know how each feels and rides. I like the aluminum frame better because it gives you a better feel for the trail. l