Originally Posted by
acroy
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
Inertia 10.89 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 ceneter 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.
I think your numbers might be a bit skewed. I'm guessing an "average" MTB commuter is not running that small of tire. Also, it depends on what you consider "nice" but I don't think 450g is particularly light for a road rim. Don't know much about nice MTB rims.
You might get truer results not using the diameter of the rims but the outside diameter of the mounted tires. MTB tires tend to be much taller though I don't know about the tire you selected.
In my case, I have 1.95s on the MTB and the 23s on my road bike so the numbers are going to be quite different.