The ongoing hookless rims saga

[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.

[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:

[fa63]

Even though technically the safety margin could be as low as 10%, I doubt engineers at major manufacturers are working with that for normal operating conditions. Enve and Giant are on record saying that they test to at least 150% of the tire rating. I imagine Zipp is in a similar boat.

Whatever caused De Gendt's failure likely falls under the "beyond design basis event" category; I don't think the tires just blew off the rim due to temperature increase or being slightly over-inflated. The question then is, would a hooked rim have held up under the same condition? I don't know the answer, but I will take any additional safety measure I can take when it comes to my wheels and tires, even if it comes at the expense of 15 grams and a little more $$$.

[fourflys]

Originally Posted by fa63

Even though technically the safety margin could be as low as 10%, I doubt engineers at major manufacturers are working with that for normal operating conditions. Enve and Giant are on record saying that they test to at least 150% of the tire rating. I imagine Zipp is in a similar boat.

Whatever caused De Gendt's failure likely falls under the "beyond design basis event" category; I don't think the tires just blew off the rim due to temperature increase or being slightly over-inflated. The question then is, would a hooked rim have held up under the same condition? I don't know the answer, but I will take any additional safety measure I can take when it comes to my wheels and tires, even if it comes at the expense of 15 grams and a little more $$$.

I generally agree, I don't think I would purposely buy hookless.. the Giant I bought happened to have hookless, so I will ride them at gravel pressures and not even think a thing about it.. or I might throw some fatter road tires on there and ride it like that and not think about it.. but I agree, if I bought a set of carbon wheels in the future for road purposes, I would more than likely search out hooked..

[MikeD]

Originally Posted by fa63

Even though technically the safety margin could be as low as 10%, I doubt engineers at major manufacturers are working with that for normal operating conditions. Enve and Giant are on record saying that they test to at least 150% of the tire rating. I imagine Zipp is in a similar boat.

I assume that they are testing new tires. Used tires and ones that have been on the rims for a while, the bead permanently stretches a bit so they don't fit the rims as snuggly. I wonder if that's at play here? My Gravel King tires fit snuggly at first, but looser if I remount them and I need to use a compressor to seat them because of air rushing out under the beads.

[fa63]

Great point. I don't know the answer, but I imagine they would have considered that during design?

Originally Posted by MikeD

I assume that they are testing new tires. Used tires and ones that have been on the rims for a while, the bead permanently stretches a bit so they don't fit the rims as snuggly. I wonder if that's at play here? My Gravel King tires fit snuggly at first, but looser if I remount them and I need to use a compressor to seat them because of air rushing out under the beads.

[RoosterCogset]

Originally Posted by MikeD

And max pressure according to this chart:

Well that's interesting.
So, if I understand -- Width As Measured is not important -- use the nominal size?
The max PSI for a 28mm tire per this chart is the 73psi amount, and per Silca's calculator, I come up with the max system weight that a 28mm setup can accommodate is about 130lbs.

So, normally the suggestion is 'use a wider tire'. Ok a 30mm tire per this chart can only be inflated to 65psi. Lo and behold, Silca's calculator indicates that roughly the same 130lb total system weight (ie. 110lb rider) is about the most that fits under this ceiling.

[Dave]

Try the Zipp pressure calculator. I put in 140 pounds to cover my weight with shoes, clothes and other stuff. It only suggests 51.3 front and 54.6 rear. Even 240 lbs comes in well below 72.5, unless thin sidewalls are specified. Then it suggest 72.6 psi for 220 pound rider.

[RoosterCogset]

Originally Posted by Dave

Try the Zipp pressure calculator. I put in 140 pounds to cover my weight with shoes, clothes and other stuff. It only suggests 51.3 front and 54.6 rear. Even 240 lbs comes in well below 72.5, unless thin sidewalls are specified. Then it suggest 72.6 psi for 220 pound rider.

Yes, because Zipp wants to claim their wheels are good for a market with up to 250lb system weights, so only when you get to that weight, will it return a 73psi value. Silca isn't selling tires or wheels.

[Mark McM]

Originally Posted by RoosterCogset

Well that's interesting.
So, if I understand -- Width As Measured is not important -- use the nominal size?
The max PSI for a 28mm tire per this chart is the 73psi amount, and per Silca's calculator, I come up with the max system weight that a 28mm setup can accommodate is about 130lbs.

So, normally the suggestion is 'use a wider tire'. Ok a 30mm tire per this chart can only be inflated to 65psi. Lo and behold, Silca's calculator indicates that roughly the same 130lb total system weight (ie. 110lb rider) is about the most that fits under this ceiling.

Tire pressure affects many properties, including comfort, handling, rolling resistance, safety, rim protection, etc. Any pressure recommendation will have to optimize for a particular balance of all these properties. The Silca pressure calculator primarily optimizes for rolling resistance. Josh Poertner of Silca has stated that most people would probably do better with a little lower resistance, for a little better comfort.

Originally Posted by Dave

Try the Zipp pressure calculator. I put in 140 pounds to cover my weight with shoes, clothes and other stuff. It only suggests 51.3 front and 54.6 rear. Even 240 lbs comes in well below 72.5, unless thin sidewalls are specified. Then it suggest 72.6 psi for 220 pound rider.

We don't know what properties the Zipp calculator optimizes for. But is interesting to note that for the same entered values for rider/bike/conditions/etc, the Zipp calculator recommends lower pressure values for hookless rims than for hooked rims. So either the Zipp calculator optimizes for a different balance of tire/ride properties for hookless vs. hooked, or it applies a fudge factor for hookless rims to keep below a set maximum.

[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.

[prototoast]

Originally Posted by Spdntrxi

I for one hope the UCI....does Diddley squat.

The UCI usually only bans things they find aesthetically unappealing in the name of safety. Things that are actually unsafe but still look good remain legal.