Conti GP5k measuring wide? Who'd have thought.... ;-)

My weight (incl. bike, etc) is almost close to yours.
I run 60psi rear, 58psi front with that tire, on smooth roads (dirt or asphalt).
If I plan to do more than a little off-road, I go 2psi less.
Anecdotally, comparing to others, this is on the high side, but I like the feel when on pavement.

No disrespect to Josh P who frequents this site, but I find the Silca calculator useless for tubeless, and still way high for tubed clinchers.

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Always felt Silca site was spot on for latex tubes; but this just seems high. This is my first year racing on tubeless; brave new world for me! From what I was reading elsewhere seems like 80's (or even high 70's) would be more inline. Not sure how much being on a 26mm tire vs 28 or 30 matters?

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2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz

Yeah, it's murky if trying to find a definitive answer. We had all the sources telling us that that we needed to dramatically lower pressures, hysteresis, etc. But more recently had some people on this forum - including those involved with rigorous testing with pro bike racers - telling us that the pressures more like what the Silca calculator spits out, are closer to optimal for real world road surfaces.

I run 87/85psi for latex tubes on the road and 5psi less when riding hardpack dirt.
When I ride 28mm Conti GP5k TR they get 57/55psi.
When riding 30mm, I go 52/50psi.

For comparison, the wife+bike are 68kg and she gets 54/52psi on her 26mm tubeless setup (she does not like squishy feeling) and -2psi when riding dirt roads.

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I suspect it's because you put in 'new roads'. Perfect pavement is going to warrant higher pressures. Is that really what you'll have? Also, you probably know this, but if you have hookless wheels, definitely don't run that pressure!

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Dimond Bikes Superfan

Seems fine to me, you're assuming a relatively narrow tire at high speed on a perfect surface. What speed are you actually anticipating? Also, as other posters have said, it's unlikely you have a surface which is actually that good. Typically people who talk about low pressures are also running 28+mm tires which measure 29+mm on rougher roads at lower speeds

I run latex tubes

205 lbs. have run 85 psi front and back per HEDs instructions when I called them, for years with the conti 5000s 25c. Never a problem

Yeah, I think 25 is still a pretty narrow tire hence the higher pressures. I’m similarly sized and run 90psi on 25’s, 80 on 28’s, and 70 on 30’s. Maybe 5 psi less if it’s wet out. Seems to work for me. Next road bike will have 32’s and 24mm internal width for sure. The extra comfort and grip is nice but still on 25/28 for tri bike.

Galveston texas; i am going to switch road surface to "worn / some cracks" brings psi down to 88. Speed should be right around 25mph.

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2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz

Several years ago, I spend an entire afternoon testing tire pressure, riding both a smooth bike path and the somewhat rougher road running parallel to it. For GP4Ks that measured 26mm on my wheels, I got 95psi for the path, and 90psi for the road. A few years later the Silca calculator came out, it recommended 95.5psi and 90.5psi. I repeated my testing when I switched to wider tires, and the Silca results were again nearly identical to what I came up with. So I feel pretty confident using whatever it recommends...

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"I'm thinking of a number between 1 and 10, and I don't know why!"

What results did you get when running tubeless on hookless at <60psi?

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no sponsors | no races | nothing to see here

Just over 4watt (at 40km/h) penalty with a 28mm tire

You didn't do that with a GP4k tire, which was released in 2007—before road hookless tubeless, before testing to validate wider (eg, 28mm) tires offers lower CdA and Crr—and 19mm-23mm tires were a thing.

And you also previously wrote about using 26mm, right?

I'm just pointing out that comparing apples to oranges does not work in this instance.

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no sponsors | no races | nothing to see here

I don't use tubeless, hookless or otherwise, so I've never tested that. Just pointing that at least in my experience, the Silca calculator was pretty much dead on, rather than "still way high for tubed clinchers"...

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"I'm thinking of a number between 1 and 10, and I don't know why!"

You are right, we did not test a GP4k
We did test 25 to 30mm, lots of 28
We tested hooked, hookless
We tested older inner widths and more modern (22, 23..)
We tested ok, good and bad roads
We tested cycling pros, tri pros, tiny women and big big men.

To what I thought was your question, running tubeless on hookless < 60PSI was never optimal unless on the really roughs roads.

Testing is believing :-)

How’s this rank vs the testing Zinn, et al did?

Anecdotally and from interviews with mechanics, etc, pressures for 28mm-30mm are <60psi.

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no sponsors | no races | nothing to see here

I have never seen the tests from Zinn. I have seen stuff for gravel but never road. To be clear, I am testing for road racing and triathlon. (as well as Belgian classics).
My tests may be 100% flawed which is why I encourage people to do their own tests.
I just find the coincidence that the numbers line up more with Silca than the other calculators interesting.

I have another 6 guys lined up in 2 weeks. One is a 7x grand tour winner. That should be fun.

Optimal tire pressure testing protocol is now part of the product we use.

If we can get rid of this pesky snow I should be able to test the fatty end of the weight spectrum :-)

Robert Chung used to add bottles to test varying weights. I wonder if he has a solution for removing weight. I am having beers with him later, I'll ask.