The ongoing hookless rims saga

[fourflys]

Originally Posted by Spdntrxi

no thanks..Jimmy is a putz

meh, to each their own.. I like his take on most things.. he's not trying to be anything other than who he is as a cyclist/human.. so much different than many in the niche..

[MikeD]

In this article https://www.cyclingweekly.com/news/u...ter-of-urgency it was quoted:

Hansen said: “This crash is why the CPA are 100 percent against hookless rims. Tires should not come off a rim. The maximum PSI these hookless tires can have put in them is 73, and if you hit something for sure it goes above the maximum 73 PSI rating on impact. That is why the tires are coming off.”

Is this really true? If you have a car up on a lift and inflate a tire to 35 psi and lower the car so the full weight of car is on the tires, the pressure is still 35 psi. That's because when weight is put on the tire, the casing stretches and the volume remains the same thus the pressure within remains the same. This is pretty much a static case, but in a dynamic situation like hitting a rock or pothole, does the pressure really rise like what is quoted above?

[jimoots]

Originally Posted by benb

But on top of that *for the rider* hookless has even less benefit over hooked tubeless on offroad bikes because the 5-10g weight savings is even less significant than on a super light road bike.

But yah, if it saves the manufacturers money and they can make it safe we will all be stuck with it.

Although if this only affects carbon personally I will just not bother with carbon wheels unless they really come down to nearly every bike.

It might sound like I’m speaking out both sides of my mouth, but stick with me please haha!

The way I see it is if there’s a cost saving and it’s safe, especially with mountain bike prices where they are, then it’s worth doing.

Every vertical is different but it’s not uncommon to hear a $1 cost saving at manufacturer level has a $5-20 impact on cost. The longer the supply chain, the more pronounced. Point being is that saving $20* at the point of manufacture on a rim could have an $800 saving for consumer on a wheelset.

(To be ultra clear, if this gets read out of context from my previous comments, this view is strictly for off road application.)

*I don’t know the actual saving, just noting that someone else on this thread pointed out it was $20 manufacturing saving to go hookless.

[jimoots]

Originally Posted by MikeD

In this article https://www.cyclingweekly.com/news/u...ter-of-urgency it was quoted:

Hansen said: “This crash is why the CPA are 100 percent against hookless rims. Tires should not come off a rim. The maximum PSI these hookless tires can have put in them is 73, and if you hit something for sure it goes above the maximum 73 PSI rating on impact. That is why the tires are coming off.”

Is this really true? If you have a car up on a lift and inflate a tire to 35 psi and lower the car so the full weight of car is on the tires, the pressure is still 35 psi. That's because when weight is put on the tire, the casing stretches and the volume remains the same thus the pressure within remains the same. This is pretty much a static case, but in a dynamic situation like hitting a rock or pothole, does the pressure really rise like what is quoted above?

I don’t know if true or not, but Hansen has been quoted with some really weird/bizarre hot takes both on this subject and the angled lever thing.

It is hard to know if he is being quoted out of context and he is a undeniably an extremely smart guy but I’ve noticed he has a tendency to take two principles and then say “logically 1+1=2”, when things often don’t work that way and are much more complex.

That gets combined with his fondness for over complicated verbiage and you get left with stuff that’s a bit nonsensical.

[Mark McM]

Originally Posted by MikeD

In this article https://www.cyclingweekly.com/news/u...ter-of-urgency it was quoted:

Hansen said: “This crash is why the CPA are 100 percent against hookless rims. Tires should not come off a rim. The maximum PSI these hookless tires can have put in them is 73, and if you hit something for sure it goes above the maximum 73 PSI rating on impact. That is why the tires are coming off.”

Is this really true? If you have a car up on a lift and inflate a tire to 35 psi and lower the car so the full weight of car is on the tires, the pressure is still 35 psi. That's because when weight is put on the tire, the casing stretches and the volume remains the same thus the pressure within remains the same. This is pretty much a static case, but in a dynamic situation like hitting a rock or pothole, does the pressure really rise like what is quoted above?

Hansen is displaying a common misunderstanding about how tires react to road loads. It is true that pressure increases as volume decreases, but as you note, there is little change in the internal air volume in a tire under load, even if you were to completely flatten the tire against the pavement. Tires support loads not by changes in air pressure, but by changes in the direction and magnitudes of casing forces. However, that's not to say that the changes in casing forces when the tire hits an obstacle might not help pull the tire off the rim. If the tire was already already close to blowing off, hitting an obstacle might cause the casing to be pulled in the right direction and with enough force to pull the bead out of the rim.

[MikeD]

Originally Posted by Mark McM

Hansen is displaying a common misunderstanding about how tires react to road loads. It is true that pressure increases as volume decreases, but as you note, there is little change in the internal air volume in a tire under load, even if you were to completely flatten the tire against the pavement. Tires support loads not by changes in air pressure, but by changes in the direction and magnitudes of casing forces. However, that's not to say that the changes in casing forces when the tire hits an obstacle might not help pull the tire off the rim. If the tire was already already close to blowing off, hitting an obstacle might cause the casing to be pulled in the right direction and with enough force to pull the bead out of the rim.

When hitting a rock or pothole, the tire could "burp." The air rushing under the bead and up the sidewall could help lift the tire bead off the rim I would think.

[glepore]

Well, you do have the case of Sagan's exploding rim...caused Roval/Specialized to pause tubeless for a full year.

And given how firm these tires are to remain on a hookless tubeless setup, I'm not so sure you couldn't see a instantaneous peak pressure spike.

Interesting point made on Geek Warning - the "margin of safety" of these systems is to a fair extent less than the margin of error of most consumer level pressure gauges etc.

If there's no benefit to me and some risk, I'll pass.

[fourflys]

I still say a huge point is we don't know what pressure these tires had in them.. were they following the hookless guidelines? Has there been a verified case of a tire blowing off (not just burping) that were being used as the manufacturer intended i.e. within acceptable pressure ranges?

[glepore]

Originally Posted by fourflys

I still say a huge point is we don't know what pressure these tires had in them.. were they following the hookless guidelines? Has there been a verified case of a tire blowing off (not just burping) that were being used as the manufacturer intended i.e. within acceptable pressure ranges?

In the deGendt case the ETRO spec called for a minimum tire size of 29 and he was using a 28, so that's likely contributing at any pressure. But the 28 on that wheel measures 30 something, so confusing. And the next "sponsor appropriate" tire was a 32, so too big. But its this kind of stuff that makes it difficult.

[MikeD]

Originally Posted by fourflys

I still say a huge point is we don't know what pressure these tires had in them.. were they following the hookless guidelines? Has there been a verified case of a tire blowing off (not just burping) that were being used as the manufacturer intended i.e. within acceptable pressure ranges?

That is a good point. I'm reading through the comments in the EscapeCollective article and someone plugged in the Pro's weight and tire size into the Silca Pressure Calculator and came up with pressures well into the 80 psi range. The max psi is supposed to be 72.5 psi.

Edit: I'm going to have to verify this because I use similar width tires and I doubt I weigh less and only use 67 psi max. according to the Silca Calculator.

[EB]

Originally Posted by MikeD

That is a good point. I'm reading through the comments in the EscapeCollective article and someone plugged in the Pro's weight and tire size into the Silca Pressure Calculator and came up with pressures well into the 80 psi range. The max psi is supposed to be 72.5 psi.

Someone should try the SRAM/Zipp calculator. The Silca calculator has always given me bizarro-world output - like laughably wrong - but maybe that's just me.

[Mark McM]

Originally Posted by MikeD

When hitting a rock or pothole, the tire could "burp." The air rushing under the bead and up the sidewall could help lift the tire bead off the rim I would think.

Burping demonstrates that the tire casing/bead have been yanked with a force of an inopportune direction and/or force. And as you say, the rush of air could create other undesired dynamics. A tire may reseat after a burp, but if there was an insufficient factor of safety (like only 10% below the blow-off pressure, as per the hookless pressure specs.), it may come off entirely instead of reseat.

[Dave]

Most tire brands approve of 28mm tires on 25mm IW rims, like the ones in question. I've been running 28 on 25mm IW rims for a couple of years. A lot of them were early model Michelins that weren't even hookless approved. The beads on one of my last Michelin tires stretched so much that the beads fell off the ledge if the air was let out to add some sealant. None ever came loose while riding. I tested new setups at 85 psi.

I run nothing but Pirelli P-Zero TLR now.

[jimoots]

Originally Posted by Dave

Most tire brands approve of 28mm tires on 25mm IW rims, like the ones in question. I've been running 28 on 25mm IW rims for a couple of years. A lot of them were early model Michelins that weren't even hookless approved. The beads on one of my last Michelin tires stretched so much that the beads fell off the ledge if the air was let out to add some sealant. None ever came loose while riding. I tested new setups at 85 psi.

I run nothing but Pirelli P-Zero TLR now.

That’s the thing. ETRTO/ISO guidelines changed 12 months ago and 29mm printed width is now the minimum for a 25mm internal width. If a tyre or rim brand approves it, they shouldn’t.

Your choices are your choices, best of luck.

[MikeD]

Originally Posted by jimoots

That’s the thing. ETRTO/ISO guidelines changed 12 months ago and 29mm printed width is now the minimum for a 25mm internal width. If a tyre or rim brand approves it, they shouldn’t.

Your choices are your choices, best of luck.

And max pressure according to this chart: