when you use the word "less" what do mean?

In contrast: For the hour record on smooth surfaces with the least "deflection" they use 22mm tires at over 250psi.

I think the oft-quoted advantage of lower pressure refers to rough or "real" roads. The softer tires spend more time in contact with the road. A tire can only transmit power and move the bike to the extent it is in contact with the road surface.

I have the new 25mm wide rims, so my 23c tire is 26.5 mm wide, with a similar air volume to a 25/26c tire. The only downside to this setup is a higher probability of sidewall cuts, since the tire shape is wider. I had a sidewall cut in the first 100 miles of the new wheels, and nothing in the last 2000 miles.

At 175 pounds on these rims, I was running 85/105 psi, and the ride seemed smooth and fast.

I recently started using 78-80 front, and 90-94 rear, and it's even more smooth and just as fast. The steering response is still quick. I'm a little more careful on rough RR track crossings to avoid rear pinch flats. On a fast group ride, I might add 5 psi front and back, since hitting potholes is somewhat more likely on those type of rides.

120/120 psi on 23c:
http://cdn.velonews.competitor.com/f...90-661x440.jpg

80/92 psi on 25c:
http://davisvanguard.org/wp-content/...hip-seal-3.jpg

I agree that the discussion is often about "rough" roads and increasing the contact patch, but this goes back to my question of how a larger contact patch by both width and length is considered "less deflection"?

A larger tire at equal pressure to the smaller tire would have a broader and shorter contact patch. This wil feel more bumpy but will be less rolling resistance.

It seems people do one change, go larger tire and higher tpi, to get lower rolling resistance, but then they screw it all up for the sake of comfort.

Just got a set of Conti 4000s II 25C and I see a max tire pressure of 120. My cuirrent tire has both a min and a max pressure (110 - 125 psi).

Would you ever inflate below minimum pressure?

Does the Conti's have a minimum pressure or is it purely a load based value?

Frank

Isn't this the same chart that pops up from time to time, and someone eventually points out that the authors subsequently published a mea culpa and retraction?

During braking and cornering there is a lot more weight on the front tire, and some of the chart recommendations are absurdly low for the front. Perhaps dangerously low.

Source?

The article is from Bicycle Quarterly and is basically the same 15% figure from Frank Berto that's been rolling around since the late 1980s. I can't find any retraction or anything else?

In a vacuum on perfect surfaces, wholly inaccurate in reality.

Nope...and for myriad reasons.

Everyone ignores tire construction in these discussions as well...this is a very complex topic. Differences in construction of same type tires can easily account for different levels of deflection in different brands/models of tires for a given size at equal pressure.

It's not the 15% so much as the assumptions over weight distribution.

Other than that, regarding the 15% I've seen what looks like different amounts of deflection depending on the tire - I suspect that it's the construction and sides specifically. Also, my observation, with respect to rolling resistance the cheaper but more flat-protecting tires have a point where lower pressure starts really making it drag, as opposed to more supple higher performance tires. I think that there are a lot more "it depends" than this chart would have it and you eventually get back around to choosing pressure for a given tire and given person by experience, or leveraging from someone else's experience.

Just take it all with a grain of salt.

I'd consider adding 10% PSI to the result obtained from the deflection calculations. It has been well argued that the original study focuses moreso on riding on consistent surface in a straight line.. ie. vs. smooth vs. rough surfaces, hard cornering at high speed, hard braking requirements, etc..

So, no retraction? No mea culpa?

?

For those who are interested in the published research ... :thumb:
25 vs. 23 | Is Wider Really Faster? | Competitive Cyclist

You misinterpret - justifying myself isn't a priority. I'm providing information only, where I saw it was lacking.

But if you want an internet "point" please take it.

100 pounds in each tire and you're good.

You have to be smarter than the tire. :thumb:

I was genuinely curious to read another dissenting opinion or see a retraction for an article that is still published on the publication's website. I disagree with your assertion that you provided any information in the first statement of your first post.

So, it appears you were mistaken? The article has not been retracted?

No, I just don't want to research that far back for this question merely to prove it at someone's request.

You can do a BF search of archives if you're interested.

This is a more recent article I believe from the same author that OP originally quoted.. not really a retraction, but maybe enough info conclude that not always is lower PSI optimal:
https://janheine.wordpress.com/2015/...re-revolution/

Without evidence of multiple experimental runs for each condition and a resulting estimate of error in the results, the data shown in that article is meaningless. The experiment might as well never have been performed. Not saying the conclusions are correct or incorrect, just that there is no way to know which end is up. If there is an estimate of error, then it should be provided with the results.

175lb rider...18lb bike...

I typically ran my 23mm Pro 4s at a punishing 100-110. After doing some reading, I decided to mess around a bit with these numbers a bit last night. Ran my rear at 100 and my front at 85. Smoother ride for sure and that I noticed, zero difference i handling. Out of saddle, hard acceleration, cornering...all seemed the same by the chatter through my hands on crappy roads seemed subdued.

I'm going to fool around with it a bit to see what I can find but it's a cool idea running the at different pressures.

As as long as you don't lower the pressure on the larger tire, yes.

larger tire but retain the higher pressure for best results....... Lower preassure is for comfort only.

Kids and comfort bikes. Kids and comfort bikes.

Never will ill you find a study where 80psi is less rolling resistance 110psi

Funny thing is the term "rolling resistance" is defined as all losses of power transmission from the wheel to the road, not just frictional. So any skipping the tire does on a rough surface that wastes energy is also rolling resistance. It is counter-intuitive to me, but there it is. So if the harder tire can't grip the road as well, I would think that would be less rolling resistance, because it can't be losing energy to friction on the road if it isn't touching it. But I would be wrong since the energy that isn't transferred from the wheel to the road due to the poor tire contact also factors into the Crr. I can't say that effect can be seen between 80 and 110 psi, but somewhere it does factor in. You won't see it on a dynamometer, only on a real road surface, the worse the road, the more pronounced the effect.

Friction, the only thing that allows you to move. :)

It's why you don't see running sprinters doing long jumps before the finish line.

Tire rolling resistance tests are only as good as what they measure. If I were a metal fixture spinning tires on a smooth steel drum, yeah, I'd probably want 23mm tires at max pressure, too.

All sounds right to me, but it may be generally hard to follow. But the question gets more interesting with this.

He is saying that we call it "rolling resistance", but some of the energy loss isn't due to the tire rolling at all! It's counter-intuitive because what we call it isn't fully descriptive of what it really is. rpenmanparker knows this but is trying to illustrate the problem.

The energy has to go somewhere (conservation of energy), and in this case it's mainly heat - flexing the tire heats it up, wind cools that off and the energy is gone. And whatever the frame and fork dissipates, but ultimately and mainly the tires.

There is also a momentum change to keep in mind. Otherwise we'd solve it all by using solid tires that won't deform but we know that's not right. I hit a bump and the front tire goes up. The vertical momentum is no longer helping me horizontally (conservation of momentum) so I slow down. I might get some of that back as long as I land on a slope angling me forward. But if my wheel lands on flat ground it will just bounce until it's all damped away.

With the tire deforming around bumps we don't get as big a momentum change, but we lose energy with the deformation. No way around it. In my view, the "right" pressure addresses a balance of these factors. That can't help but be utterly dependent on the materials of the tire, its construction, shape and size. In addition to load, speed and road surface.