Originally Posted by
njkayaker
Reduced weight has a small effect on average speed.
The cost of reducing weight starts to increase very quickly (it's a case of diminishing returns). This small effect is worth a lot to racers.
If you ride on the hoods, when not in a pace line, then riding on the drops will have a much, much larger effect on your speed. And riding in the drops is free!
You can get an idea of actual numbers by playing with something like the following.
http://www.noping.net/english/
(Note that the calculators don't take into account the effort that climbing long/steep hills requires.)
It's not just hills that less weight makes faster, it's acceleration to your max 'cruising' speed from a stop. It takes forever for me and my 27 pound bike to reach 20-21 which is how fast I can go in a straight line with a moderate effort, but every time I slow down it takes that much longer to get back to that speed. A lighter bike would probably reach that speed a few seconds shorter.
This is especially relevant in criteriums, especially ones with hills. That, and riding in traffic, or around cities.