BMC time trial coach Marco Pinotti told Cyclingnews that a 2kg difference in bike weight could give a 20-second benefit, with other seconds gained thanks to the familiarity of riding on a road bike.
Bike change could be key to Worlds TT success | Cyclingnews.com
Apparently, racers in the world championship time trial plan to change from a TT bike to a road bike due to the benefit the lighter bike will produce over just a 3 km climb. The estimate of that benefit quoted above strikes as much more significant than the small numbers people seem to cite here frequently. I'd be interested, since most of us don't have the luxury of mid-life bike swaps, to know what the difference would be riding the whole course on just a TT or just a road bike. I imagine TT would still come out on top?