An interesting post today at Velominati about racers of today being much skinnier than those of yore.
I sometimes wonder if the riders of old were heavier because their bikes were also heavier. For instance Alberto Contador weighs in at 62 kg and the UCI bike weight limit is 6.8 kg for a total climbing weight of 68.8 kg, of which the bike's ratio to the total weight of bike and rider is 9.9%.
It's reported that Merckx's bike was about 9.5 kg and that in 1968 he had slimmed to 72 kg. This would make the total riding weight of 81.5 kg, so the bike would be 11.7% of combined weight.
If Contador had to race bikes of the same weight as during Merckx's era the combined weight would be 71.5 kg and the bike's percentage of total weight would be 13.3%.
As the bike doesn't produce any power on its own, this would obviously be a significantly higher percentage of non power generating weight for a lighter rider to haul up the mountains.