Originally Posted by
cplager
I'm assuming you didn't have knobby tires on the mountain bike. Same tire pressure? Same type of tires?
It's certainly true that mountain bikes put riders in a less aerodynamic position for road bikes, but for climbing, this should matter less than for flats.
One of the main benefits of a road bike is that it puts you in a position to better output power.
As far as wheel weight making a big difference, I don't doubt that it could, but I would imagine that the tires that are run on each wheelset are making the largest difference. Not related to the tire pressure or the size of tire itself, but how supple the tires casing is. Most larger diameter tires are made with much heavier duty casing than skinny tires which are almost always produced for racing-ish purposes and not durability.