2x layers
Yes
Yes

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2013 Cannondale F-Series 29'er, Carbon 3
2012 Cannondale CAAD10-1 custom build, 14.06 lbs
2011 Specialized Crux, Alloy
2009 Specialized Roubaix Pro SL SRAM Red
1980 Palo Alto custom build

Had this issue. It happened 30 seconds before the start of a time trial! and on other moments

Wheels
old light version of the rim, 20 24, bike hub store hubs.

First it never happened with Michelin krylion carbon. Narrow black sticky tape we have at the shop el cheapo. 2 layers. Worked well.

Changed for vittoria evos and it started happening. in 23. Also had problems with non sticky tape that would slide across and expose a spoke hole. And after with sticky tape that (i think) would heat up and flat. Happened 3 times in decents. NOT GOOD!

Now I have one layer of stans 21mm yellow and all is good.

I gave up on them and bought some HEDs. (sweet stuff) Getting flats in decents and before a TT isn't worth a light rim.

Just to be clear, we are talking about the tires coming off the rim... usually many days after installation, which would indicate that the installation was not the problem.

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formerly rruff...

So can any body confirm a blow of with velo plugs?
This could be a solution.

No. Veloplugs will not fix this. There is no tape on the rim bench, so it is just like using narrow tape. Stan recommends two layers of tape all across the inside of the rim (21mm tape).

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formerly rruff...

Have used Veloplugs on the old Stan's 340s for about a year. Conti 4000s tyres and Conti Light tubes @ 100 psi. About 10,000 km, plenty of mountain climbs and descents. The odd puncture, but no blow outs to date.

Has anyone developed a hypothesis as to why this is happening yet? Is it due the 17mm internal rim width (according to a chard 17mm rims take a 25mm tyre minimum)?

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Apparently my bikes were talking the other day & are undecided whether to upgrade the current rider or get a new one...

one of the schemers...

We aren't even *certain* that it happens more with the Stans than other rims.

I've used plenty of 20mm tires that didn't come off... so I don't think a 23 is too small.

My incidents happened awhile ago, but one thing that was striking to me was how loose the tire bead became compared to when the tire was new. Since the bead pops onto a bench as the pressure is increased, it would seem that the bead is stretched more than it is on a normal rim... and maybe with time the Kevlar fibers relax or even start pulling apart. I would expect that to be very specific to the tire. The hook on the rim is also quite small compared to other rims.

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formerly rruff...

FWIW most tires I use or have used will get looser on the rim after sometime being inflated.

That would apply to vittoria, michelin & veloflex clinchers - with a variety of rims in standard formats - ambrosio / mavic / kinlin.

Would not see this as something specific to alpha340.

The channel sides that support the tyre are shorter on the Stans than others. So if the blow offs are due to tyre stretch you would expect the Stans to be more susceptible.

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r o y g b i v

I know that all beads stretch a bit, but it is a matter of degree. Plus the 340 is inherently more reliant on the bead being tight, because of the smaller hook.

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formerly rruff...

Very off topic but would you consider the 340 to be a "wide rim" like the A23, C2, C472w? The inside measurement seems to be similar, but its not 23mm wide externally how does this effect the tyre shape and ride?

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Apparently my bikes were talking the other day & are undecided whether to upgrade the current rider or get a new one...

one of the schemers...

Not only is the inner width greater, but the bead socket design also makes the tire larger and rounder. IMO it is a very nice profile... giving some improvement to ride, cornering, and rolling resistance.

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formerly rruff...

FYI, not a single problem with tubeless tires, even with no sealant. 4000 KMS so far, I think I'll always use tubeless on this rims. BTW, 23 mm IRC tubeless is 24.5 mm on these rims, check my other threads.

3 sets of the new 340 rims.
Two set up tubeless for cx and one issue on the front and one issue on the rear (both burping due to running too low PSI and hitting some sweet jumps). I run a slightly higher psi now and they have been great. No issues on the set I have set up for road with a set of vittoria rubino pros. I should be setting them up for road tubeless in the next couple weeks!