That took longer to show up here than I thought it would. Also, not sure why anyone would think 55psi is "super low" on a 28mm measured tire.

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For this to work out, based on the bumpy in the video, you'd really have to do the math on time spent in each CRR scenario.

This has been covered a thousand times over. There's been lots of videos that are more anecdotal showing riders "thinking" the higher pressure tire doing a roll down test on a gravel road to "feel" faster. Just to be proven wrong.

As for tarmac, I tend to agree you shouldn't pump it up to max.....but......what % of your route will you really benefit form the lower pressure?

My last TT bike ride outdoors was 30ish mi. I pumped up to a pretty solid 80/75 psi on 23/25 combo. I think there was a total of a minute to two minutes total accrued "rough road" that entire ride. The rest was smooth other than minute changes in texture.

It takes a pretty solid screwup in pressure choice to suffer 50w of damage for an entire ride.

Lastly, we're not pro cyclists (I'm not), but the pros on pave' run such high speeds that the spring/mass system isn't in the same ballpark as some bloke doing Paris Roubaix on vacation. Speed matters a lot to spring/mass systems being modeled like a bike tire and rider.

Yeah, agreed on the 50 watt scenario. I base my pressures more off comfort and no loss of speed, i.e. balance. Being that I am on the lighter end of the spectrum for total system weight and I don't run 22s anymore that ends up being 55/55psi front and rear, respectively, on my road bike. I'm running 23/25 schwalbe pro ones (old version) that measure out to 25 and 28 on my 19mm internal Easton wheels. They are setup tubeless. I likely ride some of the nicest pavement in the nation outside of the random broken stuff. But when I do hit that broken stuff it's not a question of am I losing 5 watts or not but how that impact impacts my ride.

Time Trial bike is a whole other animal and I will keep those trade secrets to myself. 😆

ETA: https://www.strava.com/activities/3718362217 This was this past Sunday's ride. If I am losing watts due to "low"pressure(s) then I am likely more aero on my AR than my DA. 😉

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And therein lies the rub.

Tubeless sucks, and the pressures they suggest with tubes = boatloads of pinch flats for me.

Ah well. Always a compromise somewhere.

Yeah, I think tubeless is the key here.

fwiw, I have ~5500 miles on my Pro Ones and only flatted once and really surprised it didn't destroy my wheel on impact. another time I picked up a nail and rode ~40 miles (finishing my ride) thinking I was having a bad day, but when I got home I realized pressure had dropped to ~35psi. those tires are still going after I got them sealed back up.

I know many others have not had that experience and I do ride some choice roads.

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FIFY

It sounds like you had a bad experience or something. I think you should give it another go. It's been just brilliant for me.

I honestly can't remember the last time I had to pull over on a ride for a flat. Riding is way more comfortable. I'm (apparently) faster.

Okay.

No.

You can just respond in the future. No point in changing my posts.

On a really rough surface and pressure way too high vs just right... I could believe it. Maybe.

I'd like to see some data on torque losses, particularly on a steep climb, with that fat squishy tire on the back.

I just looked at this and am looking for some advice.

I have ZIPP 858 wheels. It seems to be suggest for 303s you want to have your tubes significantly lower in pressure than I do - I perhaps feel like a moron.

What should my pressure be for relatively rough tarmac? I assume not the 100 I set them at.

https://axs.sram.com/tirepressureguide

I would use road and gravel for your surfaces and split the differences.

Lowering the psi on my 25mm TL tires on Zipp 303 NSWs was a revealing experience. I am at about 5.5-6 bar / approx. 85 psi or less.

What size are you running? What's your weight? I kept dropping until I was at 60psi and thought it was the greatest thing. Then I went down to 55psi and found the sweet spot. Such a difference.

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What's your weight? Can I assume you're running tubes?

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80kg. Yes latex tubes. Thanks in advance

Thank you. Wow I’m way too high

This entire claim should be pretty easy to validate on a real road; the white paper is based on their proprietary testing system, and they didn't actually provide much data from their third party consultant. And there's a gem on page 7.

Forgot to ask the tire width. It's kind of important. if you have a measured width that would be better than what the label says.

Also, good tool to start off is:

https://info.silca.cc/...-pressure-calculator

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Is there a better one to start (or finish) off?

Yup!

http://cdacrr.blogspot.com/

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The tested power vs speed on a "dirt road" (details on that would certainly be nice) are much less dramatic. ~12W increase going from 50 to 110 psi @35kph. Would be really cool to get this data on a variety of road surfaces.

The "gem" on page 7? Inertia plays a tiny roll as expected.

MTB studies (the Swiss National team sponsored some good ones) have long shown that the lowest "rolling resistance" on dirt comes from the widest tire you can fit and run at the lowest pressure. My suspicion is that this is mostly because, unlike on hard pavement, the surface "softness" starts coming more into play at the tire/ground interface, where a narrow and/or hard tire is going to deform that surface more than a wide/soft tire. Of course, tire measured width is a function of the internal rim width, so that plot isn't exactly an "apples to apples" comparison of the rims.

In other words, that plot shouldn't be surprising in the least :-)

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So inertia (wheel, rotating mass) is ~9W or less than 1% in a 1000+W full sprint.

Is it correctly understood:

So the difference in inertia from the Zipp 303 to, say, a lightweight low profile wheel that some people prefer for climbing or crits for “rotating mass reasons” would be much smaller than 9W and almost negligible or at least negligible compared to the aero benefits of a higher profile wheel?

Exactly. I was a bit surprised they devoted as much space as they did in that discussion to inertia. The inertia of the bike+rider system is WAY dominated by the mass of the rider and bike, and other more important properties (such as aero) are vastly more important than any rotational inertia differences between wheels.

Rotational inertia as a performance property is a "red herring"...

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Rotational inertia as a performance property is a "red herring"...

Just don't try and convince anyone of that who just bought a new pair of lightweight wheels. I get flamed so often on the Riding Gravel forum for it that I just gave up and let them stew in their ignorance. Even math does not convince them. (I used the Kraig Willet article that is clearly well done.) I like Riding Gravel for a lot of things, but the main writers reviewers are decidedly low-tech, have never used a power meter and say stuff like "the lighter wheel is noticeably quicker" and about tires "it rolls well" without providing any data at all. Other than weighing each component with a super-accurate scale. Of course, they get to test out a lot of top end stuff and no one would send them their gear if they quantified some of that stuff and said, "Your 2000 dollar wheelset" does not really do much.