Originally Posted by PeteHski

Within say 1 kg, can you really tell the difference in acceleration or climbing? If the rider weighs say 75 kg and the bike is 8 kg, then 1 kg is just over 1% of the total mass being accelerated. Bodyweight naturally varies by 1-2 kg over the course of a day, so it’s kind of in the noise.

Or to put it another way, if you are at 4W/kg FTP then 1 kg extra mass is costing you approx 4W when climbing or accelerating at FTP. It’s not nothing, but it’s mostly a perception rather than a significant loss. On the flat when up to speed, 1 kg is really nothing at all and the more aero bike will be faster.