I too ride Conti 700x23 GP4000S. And I used to inflate them to 120psi (both front & rear). Don't think I had any excessive flatting or "comfort" issues either.

But a year ago, based on the suggestion of a CAT1 racer I met cycling through Sardegna, I tried riding those same tires at 100psi (both front & rear). And it was a revelation. Now I always inflate to 100psi.

I don't flat any less than I used to at 120psi
I'm not any more "comfortable" than I was at 120psi

But holy crap the bike is so much easier to control. Fast descents on windy mountain roads are so much easier now, because the tires seem more grippy at the lower pressure. I feel more glued to the road.

This Berto chart again? This thing gets trotted out every time tire pressue threads come up.

It is wrong.

Wrong.

It is focused solely on comfort. Yes, lower pressure is more comfortable. BUT, and this is where the first error is, it also means decreased flat protect, increased tire wear and increased rolling resistance.

It is based on a 60/40 weight distribution which is fine is you only ride sitting down and never stand up, climb, corner or desend. If you do any of those things then those numbers go out the window. That is mistaken assumption number two for those keeping track.

So, if your only aim is comfort, and you are willing to sacrifice all other aspect of your tires performance and you only ride on flat roads sitting down then, by all means, follow Berto's recommended pressures and ignore what the people WHO ACTUALLY MAKE THE TIRES have to say about it.

Good for you. Why do you care about what works for others?

The magic pressure zone for tires is not overly high pressure. It also impacts the longevity of your tires. Too high and they'll prematurely square off and the rubber will thin through the middle. But cornering grip, and suppleness are revealed with lower pressures.
Stiffer sidewalls benefit most from lower pressures.

It's not wrong just because you say so. You don't even give specifics. The chart was based on rolling resistance tests. Have you personally performed rolling resistance tests? Perhaps you could show us what pressures each tire manufacturer recommends for specific rider weights? So for those of us who do stand up, climb, corner and descend maybe you could tell us what the correct weight distribution is? Do you know how much tire pressure can increase with heat? ? If you don't agree with the chart, fine. But at least bring some facts of your own.

I used to work for a German tire manufacturer you may have heard of. They performed Crr tests and I got to see all the data. Once, I even got to play with their new machine.

Weight transfer varies. I don't have data handy but know it happens since, and I hope we can agree here, we shift our body weight while riding to deal with the conditions mentioned. It also shifts during braking. Since weight distribution varies so much during riding it is an unreliable metric on which to base pressures.

Heat from riding a bicycle will not increase tire pressure to any demonstrable degree (although heat transfer from prolonged braking can). Again, are we supposed to adjust pressure of after a long descent and then pump up again for the next climb? I think we can agree that would be impractical. Perhaps finding a median pressure that handles both conditions optimally and striking a balance between them would be prudent?

Maybe we could do the same thing for grip, durability, puncture resistance and rolling resistance?

Oh wait, I think tire manufacturers do exactly that and then write those numbers on the sidewall of the tire as a range where the cross section of ALL aspects of performance intersect to the greatest degree. You can then adjust to taste.

I have a hard time believing I could use the Berto chart without getting a pinch flat. I've had one at 80 PSI on the front, and I'd have to gain over 50 pounds just to get up to that recommendation.

I think they even retracted later, because of handling issues when you load the front tire in the more high-speed cornering. The front pressure is kinda nuts anyway - when mine gets that low I get a wtf on the first turn and kick myself for neglecting the pressure for too long.

I max the tire ranged PSI for every road tire I use. I just like it that way.

700x23 Michelins 110 front, 115 rear. Comfort? If comfort was an issue I would not be cycling.

Rider info: 150 pounds. Mostly tarmac roads. Occasional gravel sectors (more so during fall/winter/spring due to college location). I seek out dirt paths whenever I can as well.

Mavic Aksium WTS: 90 front, 100 rear.

PSIMET Pacenti SL23 custom build w/ Continental GP4000s: 80 front, 90 rear.
These wheels are new (just two rides). I'm going to start playing around with pressure here later.

My first few rides I beefed the Mavic Aksium's PSI to 100 front and 110 rear. I didn't feel much difference between that and 90/100, so I stopped pushing the pump down as much so I could ride sooner.

All the guys I know who brag about their high high pressure 23's have to have them that way because of their weight.

120 is unnecessary. But the numbers on this chart are lower than minimum recommended pressures by the tire manufacturers for many riders. I am skeptical of the value of maintaining such high differentials between the front and the rear.

54 psi for a guy my size riding 23's? No thank you.

The weight on the chart is for the rider + bike + gear so that's an extra 20lbs. at least for most of us. I weigh about 160lbs + at least 20lbs for bike/gear and run my front 23@85psi and my rear 25@80psi on wide Kinlin XC-279 rims. I've never had a pinch flat in over 20k miles of riding. I feel like I could easily get away with 80psi in the front tire but don't like the squishy feel when pedaling out of the saddle.

All?

I was counting rider + gear. I'm in the low 130s and I don't carry a ton of stuff.

Granted, I did hit a pretty big pothole when I got my pinch flat, but I've hit worse since then without any problems. I typically ride 100/90, but that can vary a little depending on the tire, road conditions, etc.

Wait, it was my understanding that squared off tires were due to under inflated tires, causing a much wider contact patch and a square wear pattern on the tire. What you're saying is the exact opposite. Which is correct?