bike leaves ground

You are leaning too far forward, lean back a little so that the rear wheel has more traction. The reason why this started happening with the new bike is probally a position/frame geometery issue and not a weight issue. It probally is a very minor adjustment to your sprinting position, don't make a drastic change. When I sprint I feel the nose of the saddle just brushing the back of my legs.

a lower stem height may help. have a racer or two check it out and see if you are not applying leverage from too high a position.

jrstevens said:

I bought a new bike last month and it is very light (somewhere in the 16#range) and on my last group ride things got a little spicy and we sprinted for a few speed limit signs. I noticed that the rear wheel actually came off of the road surface on my hardest out of the saddle efforts which I've never experienceed before. I have to figure this is not a good thing in terms of attaining maximum speed. Should I be concerned and how can it be rectified; perhaps by shifting my weight back?

JS

If your new frame is stiffer than your old one, then this can also contribute to wheel jumping around. Just try to be as smooth as possible with your pedalling while out of the saddle and lean back a bit if necessary - practice makes perfect.