A question in regards to rolling resistance. Am I wrong in thinking that not everything you hit on the road with your tire effects your gas mileage? Don't tires have a tolerance in terms of how much energy they can absorb before it effects your traction, therefore effecting your gas mileage? Hypothetically, if you were driving under controlled conditions where you had every single condition about the car in a constant state.. the amount of friction on the road, the engine's RPMs, the rate of travel, drag resistance, anything and everything you can think of about the car and it's travel remains the same. That is, until it hits a tiny bump.. such as a small coin on the road or just a tiny patch of sand. If the object is small enough, there won't be enough force to effect the traction of the tire as a whole.. and if it doesn't effect the traction, it won't cause you to use up more fuel. Or is that incorrect? Now I know that road conditions are pretty much in a constant state of flux.. and that is why it could be said that everything you run over effects your gas mileage, but if you were to create a controlled system like above.. will there not be a small limit of what you can run over that won't effect your mileage? If we created a controlled system and saw that a penny lying on the road doesn't effect your gas mileage, can't it be said that there is no guarantee a penny on the road will effect your gas mileage in everyday situation? I mean, it still could effect your gas mileage in an everyday situation by having a butterfly effect on the conditions that are constantly changing already.. but I don't see it as a guarantee. That is of course if there is a tolerance the tire itself can handle before effecting it's traction and therefore effecting gas mileage. Or would you say that everything on the road (aside from the road itself) would cause you to use up more gas when you run it over? If you were driving down a road where the friction was rather stable and hit a small, flat coin, would it automatically make you use more gas to keep your forward momentum?