Originally Posted by
turky lurkey
I know it doesn't really matter for most of us, since, like you said, a slightly heavier tire only has about a 1% impact. Out of curiosity though, what do you mean about the added weight only having a factor of 1 on the hills? I guess you are talking about downhill and the fact that the extra energy needed for motion in the linear direction is eliminated by gravity, yet the extra rotational work still remains a factor? Is the extra work due to rotation the same no matter what the slope? Also, I wonder if there are some points in a ride when the extra weight actually increases speed or decreases power dissipation, perhaps because of gravity, or maybe even on the flats due to momentum (linear or angular)?
If you are moving at a constant speed, then whatever rotational energy your wheels have they will keep. So you won't need to provide any extra energy to keep them moving at that speed.
When climbing hills, people are not generally accelerating, but trying to go a (relatively) constant speed, so you just need to worry about the energy needed to lift the rider, bike, and tires up the hill. And for that calculation, the 100 g of the tires is just as important as 100 g of twinkies you just ate at the last rest stop (o.k. they don't taste as good, but)...
If you are accelerating up a hill, then you the factor will be somewhere between 1 and 2 depending on the size of the hill and how fast you are accelerating.
Another way of deciding that it isn't the heaviness of the tires that matter:
If it were because the tires were heavy, then once you were at speed, you'd find that when you stopped pedaling, you'd roll faster and farther because of all of the energy stored in the rotation of the tires. While measurable, this effect isn't noticeable. On almost all of the tires that people are complaining about them being heavy, the roll-out distance will be shorter because of the increased rolling resistance.