DMF wrote:All right, I'm not going any further into this discussion as I'm fairly convinced your idea of a real world road is alot closer to a hard wood floor than mine...To each his own, if 120psi works for you then all is well.
I never said 120psi worked for me, and it doesn't matter what my idea of a road is... or yours. We are discussing the veracity of your statement that 75-80 psi has the lowest resistance... backed by numerous tests
Has anyone else seen these tests?
The entire discussion is a little absurd.
Rolling resistance as a measured figure in a lab test is going to give you a series of figures from which a relative picking order can be established if the test is carried out correctly.
This relative order is going to keep its relation no matter what the tyre pressure or load (load being a rider's weight and a bike's weight plus the modulation of the road surface as seen by the tyre) it is submitted to for as long as you stay within a certain margin.
Extremely low or high loading or extremely high or low tyre pressure are likely to throw the picking order of lowest rolling resistance around a bit but it won't be very extreme. The worst tyre in the lab test won't become the best performer under extreme conditions and vice versa. A few exceptions notwithstanding but those are often not designed for general road use or badly designed for it at best.
IOW you just can't throw around figures of this or that pressure number is better than this or that one unless you can also define all the other parameters. Unless you do so the entire argument is bound to become a moot point. It is devoid of meaning.
Now, if you mean by wide profile wheels a widened rim bed then that also means the volume of air is being increased so it then becomes reasonable to also lower the tyre pressure of that clincher or tubeless tyre since for the same volume of air introduced to pressure inside the tyre is spread over a larger envelope.
Reasonable also means not to lower it so much that pinch flats become within shooting distance. (pertinent to clinchers)
By widening the rim bed you automatically also widen the contact patch which in turn can reduce rolling resistance.
But that also means that the thread of the tyre is a much larger part of that contact patch. That thread is inherently the least flexible part of the tyre and having that do the all the work of absorbing the load is going to throw that rolling resistance out of the window.
This really is nothing new but like everything else in engineering there's also another side to the coin.
Bottomline: high TPI count, i.e. supple tyres would always win if it weren't for puncture resistance throwing spanners in the works.
Being a snob is an expensive hobby.