The NorCal video you mentioned literally shows that, lol. Not the most rigorous test but the differences were pretty significant. There is diminishing returns at some point, it’s just that the point is surprisingly wide. Aero will start to dominate eventually.
Yes, aero will dominate eventually, but that point is not really applicable to most gravel race speeds. For the WT pros on the road, perhaps, but they are pretty quickly adopting 30 mm. Of course WT pros are averaging insanely high speeds in comparison to almost everyone on gravel. Aero concerns, re tire size, do not seem to matter to, say, Keegan Swenson and his use of a 2.2 Aspen up front, even on relatively smooth and fast gravel courses (he ran this at The Rad, which is predominantly very smooth gravel). One also does start to compromise some aspects of frame design if one wants to accommodate tires much bigger than 2.1" on a gravel bike. You might have to go to “wide” cranks, which muck up the Q-factor and are also an aero penalty, also chain stays are going to need to grow a little bit, and 2x setups may not be possible without a lot of chain stay growth. For all of those reasons, 50 mm to 2.1 or 2.2 may be the natural sweet spot for gravel before things start going awry too much.
I think that Schwalbe is in the process of simplifying things a bit. They introduced the Rick with only a single casing, the new “Pro” casing. I suspect many of their other MTB offerings will follow suit, with the “Super Race” “Super Ground” options disappearing and being replaced by just the single “Pro” option. Of course they will still likely need some tires at a lower price point, but racers probably will not be concerned with those tires anyway.
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It isn’t really my focus, but am I reading this correctly that nobody has done any sort of solid outdoor CRR testing on 28 v 32 gp5k?
TBH that blows my mind
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No one
But brr did compare the 23,25,28,32 gp5k
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Welcome to my world. Most people haven’t a clue on how to do a careful test.
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Goodness.
Aight.
TR members that wanna know this showdown, get your nickels together, send me some tires and I’ll do it. Pavement and cat 1 gravel.
Second behind another tire project but someone has gotta do this 
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I’ve got GP5k AS 32s on my bike right now. Ready to test when you are.
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Yesssss let’s hit it soon.
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Yes my bad, I got the point that it diminishes wrong. He tested 28mm/32mm/34mm tyres (Vittoria Corsa Next) and the 32mm were fastest but 34mm were slower. I don’t think that really affects my point, there is a point on the spectrum that wider gets slower, and that spectrum changes based on the unique characteristics of every course.
Just for interest, the 28 is the fastest of the variants on BRR (although at high pressure, versus low pressure for the wider tyres, maybe someone with premium can comment with more data).
Apologies this is getting a little away from the OP, but painting a fuller picture helps give context to it all. A comparison of Conti 5K S-TR from 25mm to 32mm on tarmac would be amazing, but that would be an expensive test and using used/worn tyres would likely impact the RR quite considerably.
Maybe you can set up something like BRR where we can donate and vote on some tyres to test, you can buy them and then sell them so the cost per test isn’t too high?
I think what I’m going to try is just request certain tires and folks can buy them
And ship to me. Once I’m done they can have them back or I can donate locally.
My main thing I need at the moment is a set of Caracal Race 40s! Already had someone volunteer to buy and ship, finding them in the US is tough.
Posting requests on my IG as I go.
https://www.instagram.com/flexfitbyjohn?igsh=enFya2wwaXpraThk&utm_source=qr
I don’t wanna have a bunch of tires, money, and peoples tire dreams tied up in a money pool. It is a somewhat legit option still.
Oh and regarding CRR losses with worn out tires… maybe. Def not tangling with that one 
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or improvements 
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IIRC, when Al Morrison was doing roller testing for Crr, he noticed that brand new never-used tires had slightly higher Crr, but that difference disappeared pretty quickly (like, after 20 or 30 km on the rollers). Because the effect disappeared so quickly, it was hard to figure out a reason or mechanism. But these were road tires.
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I’m wondering if anyone has any thoughts about radial tires making it to the XC/gravel side.
All the MTB reviews claim how much more supple the side walls are, which I could imagine could make a faster tire on very chunky gravel where the tire is being flexed close to bottom out with significant frequency, but likely limited improvements on smoother gravel, where the tread side of the carcass isn’t really much softer? Im not sure if that last part is true, but my read on what they are doing.
That kinda tracks with suggestions to ride some to get the mold release stuff off of tires. (No idea if that’s legit or not)
Historically, I usually tell people I coach if they are doing new tires, get them a week or two before a race… not a day or two.
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Just for clarification on the Race King. This is the faster version yeah?
I’m looking to get one for my Revolt (I think it’ll fit in the fork!) and maybe a pair to try for my xc on certain tracks.
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I asked the Schwalbe reps this exact question when chatting with them at SBT GRVL. They said that a radial would probably not end up being faster for gravel, as it results in a larger contact patch, and in most cases, that larger contact patch is going to result in more rolling resistance. But I could imagine, under some conditions, it might be faster. By no means were they certain of the results, as they have not made XC or gravel tires (yet) with the radial approach. They seemed to be holding back a bit on what they wanted to reveal, but it did seem that radial XC tires were at least going to be tested in house.
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Awesome, thanks for that, will be interesting to watch for
I’m not sure size of the contact patch is the only thing that determines rolling resistance.
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