read jc's post: http://bicyclesports.com/...wPost.aspx?PostID=30

Thanks for looking around my site, I put this here to answer these types of questions and I'll try to do it as often as possible. Water bottles on bikes, this might get a little long.....
When I first started testing that, frames were small diameter steel tubing so a bottle on the down tube really stood out. Bikes at that time didn't even come with seat tube w/b bosses. We started making some aero steel tubes but this made d/t bottles look even worse so we started putting them behind the seats to hide them. In the 90's carbon tubes and aero oversize aluminum tubes started showing up along with front mounted water systems. I had not really retested water bottles in a good while so in '98 I spent some more time [and money] testing bottles and their positioning. I was working on a new TT bike for Lance and we were trying several things, one being the ill fated "bladder" for water. During that testing we did discover that the tube that stuck up out of a front bottle caused really big drag, the front bottles weren't to bad, but the tubes that stick out in your face take about as much energy as a 3 spoke wheel can save. We found that an aero w/bottle on the seat tube really worked pretty good and added surface area in crosswinds which will give a little more speed. On the newer style Alum. and carbon [larger diameter] aero frames, a round seat tube bottle doesn't hurt very much and in the right crosswinds can actually help a little bit. Round bottles on the downtube are generally not the best for aero, but cause less of a problem than the straw on a front bottle system. Rear moounted bottles that stick way up in the air are not very good for a couple of reasons, it's hard to get your leg over them and they disrupt the air coming down your back. Lower mounted rear bottles are about the same as a down tube mounted bottle, which ever is easiest for you to get in and out would be the choice. For most people riding without water is not a good thing, Camelbacs work very well and never hurt the aerodynamics hardly at all.
Thanks,
J Cobb