worf928

See your statement that I quoted in this post:

https://rennlist.com/forums/928-foru...l#post11837941

mark kibort

as I said, I didn't mean that going up and then going down would counteract the energy use entirely, but what I meant to say , and I said later, was that it just reduces the loss of climbing the hill as far as fuel efficiency. I think most would agree, that going up to the mountans and then down again, is only a 10% loss of MPG vs just flat line travel, but stopping at the top and filling up is more like a 25% loss in MPG.

bottom line, going up or down, the rolling weight at a constant speed is no more of a factor than it is sitting in the car.

worf928

http://en.wikipedia.org/wiki/Rolling_resistance

mark kibort

Your point?

rolling weight is not rolling resistance. although it can effect it. You have to read a little more carefully.

the entire premise of the fight here, is that rolling resistance and drag are the only real factors of adding weight to a car in its wheels and effecting fuel efficiency, NOT the fact that the weight is rolling. (rotational mass vs translational mass in the amount we are discussing here...... 5-10lbs per wheel)
whether the weight is spinning or in the car, the rolling resistance will be the same... this we all know.

so, again, if you are not changing speed, even climbing hills or not, that spinning weight has the same effect as if it was sitting in the car... if you are accelerating, then its effect is less than 1.5x that if it was siting in the car.
and 10lbs of extra wheel weigh , 40lbs for all 4, wont change MPG all that much, if at all. in acceleration, 40lbs acting like 60lbs would have a very small effect.

btw: from that link, which is good for rolling resistance description... something we all agree that is the cause for loss of MPG

"Diameter effects seem to be negligible, provided the pavement is hard and the range of diameters is limited. See sectionDepends on diameter"

mark kibort

Just ran through a few more calculations for a wheel having the added weight on it. If it's a uniform addition, the extra effect on the cars overall inertia will be less than 20% as if that weight was in the car. Not a big deal as many has thought. As I mentioned, the most you can ever have, is an effect of 2x that weight as if it was in the car, (translational inertia can only equal its Rotational inertia, if the wheel and tire is not slipping. And the key point, it cant be any more than 2x, and only if you add the weight to the tire tread.