Originally Posted by
catatonic
Keep in mind how inertia works. You have to surpass the weight of the object to get it moving, from that point on, you are just deal ing with tthe raw weight of the object at hand. This is based on sliding a non-rolling object.
Now, when you are dealing with a wheel....you don't have to go beyond it's own weight to get it moving. weight is directly proportional to inertia...this matters later.
Now you got that wheel spinning, notice how fast that light wheel feels? That's because it takes less force to get it up to a certain speed...now what happens at that speed? nothing...the power output to hold that speed is almsot identical between that wheel and a 2kg wheelset. Now, when you stop pedaling...you will notice something else....the heavier wheelset has a slightly lower deceleration factor, due to inertia.
Really, In my opinion, lighter wheels are nice for climbing, but there is no real gain in having stupid light wheels.
Go look at cars...rotating weight is not much of a concern, as much as unsprung weight is. However roadbikes do not have suspensions...so it's a moot point. Then factor in how little a bike weights in comparison to a pro racer, and you have an even smaller gain for lots of cash.
Wrong!!!!
The kinetic energy of objects moving
linearly is described by K=1/2mv^2; where m= mass and v= velocity.
The kinetic energy of objects moving
rotationally is described by K=1/2Iw^2; where I=inertia and w= angular velocity (rads/second).
I=mr^2; where m= mass and r= radius
As you can see the mass of the rotating object
is relevant. It not only takes more energy to get a rotating object with more mass (i.e. heavier) up to a specific velocity, it takes more energy to keep it at that velocity.
K= 1/2Iw^2 applies if you only wish to rotate the object.
If the rotating object is a bicycle wheel and you intend to use the rotating wheels to move the bicycle along a linear path, then you must account for angular kinetic energy to spin the wheels and for translational kinetic energy to move them in a linear fashion. From the identities listed above mass is a factor in both. K (for both rotation and translation)= 1/2 wmr^2 + 1/2mv^2; m being mass.
With respect to the car analogy, the unsprung weight
is predominately the rotating weight. The rotating wheels of the car are most of the unsprung weight, that being the weight
not supported by the springs. The reason that the wheels are such a big concern is because, as has been addressed above, there is a need to consider momentum and kinetic energy in the rotational and translational domains.
Lack of a suspension does not make this a moot point. the principle is the same. The greatest advantage comes when you reduce the rotating mass. There is sound reasoning why upgrading to lighter wheels is a priority to upgrading to a lighter frame.