PS- you want to send yours out so I can prove it for you or maybe just do the experiment on your car.
As I mentioned before, I have done that experiement before. Going from 35 PSI to 60 PSI yielded 96 MPG and 98.5 MPG respectively on the Prius Marathon route. That is only a 2.5% increase, and like I said before, in your case that would amount to less than 1%. So it appears that we have conflicting data. I posted the info about a year ago on GH and some other forums. If someone wants the particulars I would be happy to search for them.
you're comparing oranges to apples. A fully gasolene car acts way different than a hybrid.
Both cars get all of thier power from gasoline. Both cars run on tires and rolling resistance is a common feature. The fact that the car is a hybrid will have no effect it's ability to overcome rolling resistance. Therefore, apple = apple.
some have even stated that they didn't see a fuel economy improvement when over inflating the tires. Then please explain how I gain 100 more miles per tank??? I even drive on the streets more than the freeway.
The weather has made a much larger difference in my car than you are claiming tires have made for you.
Rolling resistance is not a big enough factor to affect that kind of change. You could eliminate all rolling resistance and you would not have that improvement.
Unsubstantiated claims like this are the same as "so I slaughtered a goat the other night during a blue moon and put it's blood it my tank. I got a 40% inscrease from the blood's mystical powers. Previously I only slaughtered goats on regular full moons, which only resulted in a 10% increase."
On tire pressure's, my perspective of the rolling resistance is that it is largely due to the flexing of the sidewalls of the tire, as the tire rotates. From a standpoint of how much air the tire can be inflated to, I am pretty sure the figures on the sidewall's are very conservative. However, I have run tire's as high as 55-60 lbs., with some very heavy load's and when I run them high I have never had a tire failure, crossing the desert, in the summer, in the daytime.
I was running 35 lbs. in the front and rear tires on my 89 Wagovan and it seemed to be getting in the high 20's, low 30's range. However, I shifted them recently to 55 lbs, which does make it ride a bit bumpier, but which I seem to be getting more in the range of 35-40. I don't know how much it increased the overall mileage, but I know from a coast, out of gear perspective, it seems to me like it rolls a lot further now, than it did before.
I think that a couple of additional factor's are also coming into play in trying to compare. First, I suspect that different tire's have differing amounts of rolling resistance, depending on what they use for the sidewalls, rubber and so forth. Second, I think a large factor, also, is that it may depend a great deal on the weight of the car. I belive that what Compaq888 is experiencing may partially be a reflection of the fact that a Nissan Altima is a substantially heavier vehicle than a Civic or a particularly a Geo of some kind. I suspect that 35 lbs in a lighter car might be similar to 40 or 45 lbs in a heavier car, in terms of how much the sidewall's flex and how much additional drag they add to the car.
I think that one factor to consider is how much of the tread is actually down on the road. It seems to me like their is probably some tradeoff's on tire pressure, mileage, traction and overall ride quality.
My primary concern, keeping mileage in mind, is to not get my tire's so high that they become unsafe from a tread contact perspective. The question I don't really have an answer for is how high I can go before I start getting only tread down the middle of the tire's.
I have a small ex camp trailer/utility trailer that I have used for hauling all of the families combined gear on camping trip's/vacations. It now has the skinny 12 inch tire's, which was a upgrade from the original 8 inch one's. I have blown tire's on it, at 75 lbs, driving across the desert, in the daytime. However, I put them up to about 110 lbs, and the tires no longer touched all of the way across the tire, but I also quit blowing out tire's, so I left them alone, at the time. I figured since I was pulling the trailer, if it blew out because I had it to high, it wasn't any bigger deal than the blow out's when I had them at 75.
I am not recomending that anyone run their tire's at higher than the sidewall rating on the tire's. I am saying that based upon my personal experience's, I don't think that raising the tire pressure increases the risk of any type of tire failure, but again that is just based upon my experience's.