Originally Posted by
cplager
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.
I'm not crispy on the physics, but I don't understand how hill climbing cannot be anything but a series of accelerations, when between each stroke, you not only have rolling resistance slowing you, but also gravity working to pull you back downhill?
Maybe I'm understanding this all wrong, but any time you need to apply enough force to the pedals to make the wheel spin faster (regardless of road speed, which may be dropping, as on a hill) , a heavier tire will require more force than a lighter one.
It's tempting to think it's inconsequential, that amount of extra force, but depending on how much effort you put into, and appreciation you have of, going faster and/or with less effort, the more it matters, as it does the greater the weight differential becomes. An extra 100gm per tire over a 210gm lightweight for a 5mi cruise across town matters not, but NOBODY is hammering out a hilly 70 mile ride at high average speeds on 1900gm worth of tires. That ain't happenin'.