If you are talking overall bike weight it's not that significant if you're heavy. But there are some parts of the bike where weight matters more than others. the frame, handle bars and seat and seat post and stuff like that is stationary when you ride. Things like your rims and Hubs and pedals are very important though. The less weight you have to make go around the better off you're going to be. Overall though, lose weight on yourself and then worry about your bike