Honestly the Aero 30 is the only hydration system that we have ever tested that gives big reductions in drag over a bare bike. Two guys that went to ERO sports recently contacted us to tell us they had a -7 and -9 watt reduction in drag on their Felt IAs. They gave us their data and are allowing us to publish it. We have seen this similar reduction from other tests including Starky's bike. Usually the closer you can get the Aero 30 to the head tube, the larger the drag reduction.
BTA systems in all tests we have seen are a slight reduction to neutral at best, 3-6 watt reduction at worst for one particular brand(those results are dependent on factors such as width between extensions, size of arms, etc). Having said that we designed the AeroZ to be the most aero shaped BTA system possible. By using our same aeromount we were not restricted in the units shape to fit into a standard cage. Meaning we have optimized frontal camber AND taper.
Hans
Hans Bielat
TorHans LLC Co-Founder, Owner, Chief Innovation Officer
http://www.torhans.com