By memory I believe the max psi on my 404 s said 116.

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I *heart* weak, dumb ass people...

For the 404FC Carbon Clinchers, max pressure is 125 psi

Related, here's the recommended pressure chart for Zipp tangente tires:

These come off the traditional Zipp wheels, not attached to the Firecrests on the website. Everywhere I have read, "they" recommend lower pressures for the wider rims, but I too have not seen a table for the FC's based on weight. I know a few people at Zipp, will check and get back to this post if I get any info...

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Colorado Triathlon Company, CO2UT 2021, Crooked Gravel 2022, Steamboat Gravel 2022

Pulled out the user manual. Says...

"Do not exceed 125psi when inflating tires on clincher rims."

Not sure where I got the 116.

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I *heart* weak, dumb ass people...

With my Hed Jet 9 (which are also wider), they recommend max 105psi.

From Hed Q&A:

Q. Dear Mr. Hedtech, how much PSI should I run in my C2 rims?

A. Our wider C2 rims should be run at AT LEAST 11% lower pressure than you would use in the same tires on a 19mm rim. I weigh 165 lbs and run 22mm tires at 80-90 psi. Because the C2 rim is wider, your tire's air volume is greater than it would be on a 19mm rim and PSI needs to decrease.

Excessive pressure will do two things:
- Compress the rim slightly and decrease spoke tension
- Harden the tire to such a degree that it no longer has the small amount of flex that it would have at a lower pressure or on a narrower rim. The flex is both lateral and vertical. In the case of the wheel rubbing the brakes or frame, lateral flex is what we are concerned with. As frames and wheels have gotten stiffer and stiffer over the past decade, torsional force on a bike has gotten more noticeable.

Very intertested in the follow up to this. Racing at IM Texas this weekend, and this will be one of my first few rides on a new set of carbon clincher 404 FC's. Honestly, had not even considered doing anything different. Very happy to be getting an education. Thanks for posting if you hear more.

A. Our wider C2 rims should be run at AT LEAST 11% lower pressure than you would use in the same tires on a 19mm rim. I weigh 165 lbs and run 22mm tires at 80-90 psi. Because the C2 rim is wider, your tire's air volume is greater than it would be on a 19mm rim and PSI needs to decrease.

That's code for "the wider rim alters the tire profile in a way that will result in a harsher ride if you don't drop the pressure." You'll also experience higher rolling resistance... but nobody notices that.

Has this been field test confirmed yet, and do we know the extent to which this would be true?

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

Not field test, but lab test confirmed.

Pop quiz: What tire mechanism does the rim stand on?

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

When these first came out I thought there was a conflict between claiming a smoother ride *and* having greater pinch flat resistance. If the tire is vertically stiffer, then it's less likely to pinch... but also rougher riding. I think they are capitalizing on the fact that most people ride with pressure too high... so if you tell them to lower the pressure significantly they will notice a smoother ride. The "handling feel" part might have some validity... though I certainly don't notice my 23mm tires "flopping around" on my 19mm rims on hard switchback descents.

Al (AFM) tested the Crr on rollers. There was no detectable difference between a wide rim and a narrow rim with pressure the same. Lower pressure (down to 80-90psi) increases resistance unless the surface is quite rough.

http://books.google.com/...ge&q&f=false

Link takes me to Encyclopaedia Brittanica with the search phrase"
"How a pneumatic tire supports its load"
But I get no content.
Got a page number or other way I can find what you have in mind?

Would love to learn it's been long understood.

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

Interesting, what kind of CRR loss are we likely suffering with the new wide rims?



compressed air? the sidewall? both?

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

I take a stab
A pneumatic tire doesn't support its load, the load is hung from the top.

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Styrrell

For Crr, I was thinking of Al's test data, which rruff already referred to.

For supporting the rim, you guessed it - all of the above. The rim is supported by the shortening of the vertical component of the tire casing's tension vector as its angle changes where it departs from the rim's edge.

Given that, how would you say a wider rim changes the tire casing's tension vector angle? And how does the tire's spring constant change as a result?

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

Sorry styrrell, the rim stands on the tire near the ground.

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

p.1007 has the beginning of the discussion you're looking for, sort of.

I'd imagine the wider rim, in most cases would preserve the sidewall's vertical angle. As such it should be stiffer.

I'm pretty surprised they didn't update the chart for the Firecrest wheels.

Did anyone email Zipp and ask? Or Josh who posts here?

Someone do it so I don't have to?

totally get the theory. but no idea if the difference would be losing 10 watts, 2 watts, 0.001 watts, etc.

If its something on the order of 0.1 watts, then for road racing the wider rims working better with 23mm tires would still be clearly worth it.

If its ~5 watts, then damnit quick making me adjust my brakes to put on race wheels, HED, and Zipp =)

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

  

Should we be considering running 25mm tires on our wider rims?

im gonna get a mountain bike, and go pro

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

Thanks.

I am assuming similar to the HED's but thought I would check. I am 180lbs and run 95psi on Jet 6's. I toyed with quite a few pressures and this feels about right for me.

If you could let me know what Zipp say that would be great, thanks.

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https://www.pbandjcoaching.com
https://www.thisbigroadtrip.com

totally get the theory. but no idea if the difference would be losing 10 watts, 2 watts, 0.001 watts, etc.

~0? Damon was referring to the "smoothness" of the ride. I don't think he was implying that the Crr was higher.

the two are related

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter