I can't resist: here's an Inertia calculation:

I=MR^2
Diam Diam
MTB 22 Road 24.5

Mass (atb/road):

rim 400 rim 450
tube 150 tube 150
tire 350 tire 300
total 900 total 900

MTB Inertia 10.89 Road Inertia 14
road = 124% mtb

This shows the road bike has 20-25% more inertia in the wheels.

Assumptions:

-Discounts the spokes, nipples, hub, etc. Inertia is related to the square of the radius, so stuff close to the center of rotation doesn't matter much anyway.

-uses the "true" diameter of mtb rims (22") and 700c rims (24.5")

-rim: nice mtb rim of around 400g, nice road rim of around 450g.

-tube: i figure about the same for each, around 150g

-tire: i used the "Nashbar Slick" wire bead 26x1.25 and Duro Road folding bead 700x26c tires. about what the *average* commuter uses... just a guess cause I havta put something there.

the "inertia" number is just an index to compare one to the other. feel free to plug into your own spreadsheet & play around. edited for readability - copy/paste from execl to bf is iffy.