Originally Posted by
old's'cool
When you accelerate your bike with your own effort, you are adding kinetic energy to all parts of the bike. In the first place, linear kinetic energy in proportion to the total mass and the difference in the square of the velocity (i.e. before and after the acceleration). To get the rotating components (most importantly the rims and tires) rotating at the higher rate corresponding to the linear velocity change, you must also add extra rotational kinetic energy to them, above and beyond the linear energy. That is why rim and tire weight counts for more (approximately 4x) than non-rotating components when it comes to acceleration.
I get lost at the 4x.
Looking at the equations (I'm assuming they are correct, but I am no physicist) here,
Moment of Inertia
There is really no difference between linear and angular momentum other than linear inertia is controlled by mass and angular inertia is controlled by the mass and distance.
But then there is the Alp D'Huez experiment. The same wattage created the same results whether the extra weight was on the wheels or the frame. And because of gravity, if you are going uphill at a constant velocity, you are always accelerating by fighting the deacceleration of gravity.
So where is the 4x coming from? Pardon my ignorance but I'm trying to find the governing equation. Is it related to the rate of acceleration? Even though the gradient at Alp D'Huez averages about 8%, the acceleration still would be considered "low". And if your acceleration rate is "low", moment of inertia is negligible compared to the linear inertia. So the 4x comes into play not if you are slowly getting up to top speed, but if you do a burst to top speed, the 4x comes into play. Just my guess right now. Any truth to it? But if rate of acceleration matters, what is the equation that says so?