Originally Posted by Drew Eckhardt

A 145 pound climber atop a 15 pound bike would loose 1.2% of his speed up a steep hill which is 45 seconds an hour and a 200 pound Clydestale on a 20 pound bike would be down by .9%.

On flat ground both riders would take an extra .1 kilojoules to propel themselves from zero to thirty MPH.

At 300W average the 145 pound rider would loose .2 seconds in a standing 500 meters dropping from 52.2 to 52.4 seconds.

The effect on flat ground speed would not be measurable assuming aerodynamics were the same; although deeper weight on aluminum rims (DT 565 vs. 465) often implies more depth which would make for a faster ride in spite of the extra pounds.

Except for psychological impact (perhaps by way of things like sound) the loss would be effectively non-existent except in some racing situations, like where a climber who was otherwise competitive was riding off the front to an up-hill finish in a mountain hill climb.