The pro to lightening a bike is more speed/easier going. The cons are price and the fact that some lighter compenents aren't as strong.
Realise that if you're not racing,it's prolly not worth it to spend big bucks to drop a pound or two. Also,for a comfort bike like yours,you'd prolly be better off just getting a different bike. For what you'd spend to get the weight down significantly,you could just buy a performance hybrid or road bike.
There are two changes you could do that would really help without costing a fortune. First,and easiest,is the tires. Swapping them for something thinner/smoother/lighter/higher pressure will give you a noticable increase in performance. If you mainly ride in the street,I'd suggest some WTB Slickasaurus or Specialized Nimbus Flak Jackets in 1.5". Second,if you have a suspension fork,swap it for a rigid. You'll save weight and you won't have to deal with the dampening effect caused by suspension. These two things will give you the best bang for your buck in terms of lightening your ride and increasing your speed.
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C'dale BBU('05 and '09)/Super Six/Hooligan8and 3,Kona Dew Deluxe,Novara Buzz/Safari,Surly Big Dummy,Marin Pt Reyes,Giant Defy 1,Schwinn DBX SuperSport,Dahon Speed Pro TT,Brompton S6L/S2E-X
