PSI for road bike tires?

[Seajay]

the amount of energy lost bouncing vertically is probably adequately absorbed by the tire, fork, and rider such that it's still going to be a faster tire.

Yes, Fun conversation. Thank you for continuing it.
I will stand by my theory that the energy the fork, frame and rider absorb (convert) is wasted. Yes, you can run too soft... but with an appropriately inflated tire, energy taken up by the front of the contact patch and returned at the aft is not wasted....thus a faster more efficient set up.
It would be interesting to do the same road with a powermeter and a speedometer. How much power does it take to hold X mph with a range of tire pressures?
We need a tire engineer to jump in here.

[aicabsolut]

Yeah, sure it's wasted energy, but I think that it's negligible compared to the vertical shock absorption being done by the tire/fork/frame/rider with a softer tire in light of the differences in propelling forward. The more I think about it, I think you are right that you've got to measure this in terms of power output by the rider instead of just rolling resistance numbers for a tire since travel in the vertical direction would be hard to measure. The fewer watts it takes to go X mph over different terrain with different pressures under the same wind conditions would mean that the tire setup is "faster" because the ride would be more efficient.

I'm not sure how many watts we'd be talking, though. I would guess not that many, based on my assumption that this topic eventually boils down to personal preference for comfort, the road "feel" for a given tire, and the odds of getting a pinch flat due to ease of compressing the tire.

[Seajay]

From Zipp Tech without changes except highlights.
OK I'm a tire geek. I admit it.

The Corsa Evo CS will be perfect for that wheel, and I would recommend 100-125 psi (6.9-8.6 bar) depending on your weight. You will want to run 0.2-0.5bar more in the rear than the front to account for weight bias. I personally weigh 155lbs (70kg) and run my tires at 105 psi front (7.2 bar) and 110 psi (7.6 bar) in the rear. When I was racing and lighter I ran them at 100/105, but now that I'm heavier it is safer to run a few extra psi and I may go even higher on bad roads, which has worse rolling resistance, but better protects the wheels from damage in the event of hitting a pothole or something else which could damage a rim or tire. The better option is to run a wider tire at lower pressure on rough roads, but that is just not always feasible, so I would rather have higher rolling resistance and protect the wheels than lower rolling resistance and increased risk of damage to the wheel.

Higher pressure is definitely slower on anything other than perfect surfaces. Think of it in terms of a bunch of 1mm tall bumps in the road. If you have a lower tire pressure, the casing of the tire will deflect over each bump (we'll assume the casing deflects the entire 1mm) converting a small amount of energy into heat as the casing deflects, but the amount of energy necessary to compress the air is almost non-existent. Now at a higher pressure, we will assume that the tire deflects half as much. Now the bike and rider are lifted by 0.5mm and the casing deflects by .5mm, the energy necessary to deflect the casing by .5mm is less than it takes to deflect it by 1mm, but is nothing compared to the amount of energy necessary to lift the bike and rider by 0.5mm, so the end result is that the total energy requirement for the high tire pressure condition is much greater.

The other thing that happens is that on smoother roads, high tire pressures keep the casing from deforming over and into small cracks and crevices and over pebbles, which means that some of the deflection is transferred into the tire tread, which is not as elastic as the casing. Excessive tire wear comes about as the tire rubber begins to fail in shear as it is deformed by the road surface, and this generates heat as well as breaks down the cross-linking within the tread material.... overall, you are using more energy to go slower and you're wearing your tires out faster. The problem is that high tire pressures feel fast as your body perceives all the high frequency vibrations from the road surface as being faster than a smooth ride.

Lennard Zinn had a great analogy when he said that 100kph in a Jeep will scare the crap out of you but 200kph in an S class Mercedes feels effortless...the same is true of bike tire pressures, but it's just hard to convince ourselves of that. As athletes we tend to buy into the 'if some is good, more must be better' philosophy, but this is rarely true. Of course the tire manufacturers have given up on this and continue to try and make higher pressure tires as that's what the consumers demand, as I think that they've decided that it is easier to just give people what they think they want than to try to educate and argue with them :-)