So... 340 owners... have you ever experienced a tire inexplicably blowing off the rim? Any details you can provide (even if the answer is no) would be helpful. Things like taping, tires used, tubes used, etc.

I'm sure this doesn't happen very often, else I would have heard more about it. But it has happened twice to me... and I recently discovered that is has happened 3 times to someone else. Lumping both of our experiences together:

Rims are the older 340 models (the light ones).
Tubed setup. Twice with latex tubes, the rest with butyl. Tires have been GP4000S x2, Michelin Pro3 x2, Vittoria Corsa CX.
Tires always blew off days and hundreds of miles after mounting. No warning or indication.
Neither of us has had a tire blow off any other rim... ever. We are careful with mounting. I have ridden ~200k road miles, and he has ~100k.
Pressure <110psi.
No braking or cornering or sprinting forces were involved.
Tires were either indoors or outside being ridden in <80 deg temperatures when they exploded.
Wheels were taped with two layers of Stan's 12mm tape. Tape comes partially onto the rim "bench" but does no extend into the bead socket.

I asked Stan about it. He mentioned that having the tape extend all the way to the bead socket is important. Notubes uses two layers of 21mm tape (not 12mm) and Stan says they haven't had any tires blow off the wheels they sell. I thought it was a potential problem to use 21mm tape because it is impossible to keep it out of the bead socket, but he said it didn't matter... that little hook in the bead socket didn't do much anyway... the tightness of the bead on the rim "bench" is what really keeps the tire on.

So does two layers of tape really make that much difference to the tire bead? I measured the tape and did some quick calculations, and it amounts to over 2mm of linear bead stretch. I can't tell if that makes a big difference or not, but it is something.

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formerly rruff...

I got the older 340 on the front . Its got the yellow rim tape and I use michelin air comp tubes and zx clinchers. No issues what so ever . Psi is 110 /120 max . The wheel weighs 490 grms . 18 spokes .
On the rear 24 spokes, I switched to the new rim gained 10 grms ,692grms but running fine as well ...

Two layers of 21mm tape?

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formerly rruff...

I have one experience a GP4000S tire blown off the older Alpha 340. Tires ridden couple of hundred miles without problem, pump up the tire to 100 PSI the night before the ride, tire blew off 4 hours later. Reinstalled the tire with new tubes and have 2-3 rides with it without any further problem

Same question to you... how was the rim taped?

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formerly rruff...

I just Have 1 layer of the yellow rim tape. Im pretty sure it's the tape Stan's recommend. It is all the way round on the flat of the rim , obviously with a hole to stick the valve in .It's very thin.

You need Two layers of 21mm tape all the way around.

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Yep... for two reasons... keeping the tube out of the holes and keeping the tire on the rim.

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formerly rruff...

I use wide velox tape (22mm) & ran a spatula around the rim hook to ensure clear. Have about 6k kms on two wheel sets, 3nr rims being the older lighter version. Run both butyl & latex depending on conditions & whats available.

All kinds of riding & conditions, no problems at all. Michelin Pro3 for about 4k kms & Pro4 for 2k kms.

If anything the michelin tire is too tight. You have to use a lever to bring the tire off & have to sink the tire into the recess all the way around the rim to get enough 'give' to even considering getting michelins off the rim.

Did have a couple of problems with pinching latex tubes when mounting initially but have learnt that the tube needs to be carefully inserted & then moved into the body of the tire by ensuring the beads of the tire seat on the middle channel prior to inflation. Bit fiddly especially if cold / wet, but its no biggie once done a few times over.

That's my experience with them. Hope that helps in some way
Nice rim, just a touch too expensive imo...

My wheels are handbuilt and I just presumed that was 1 layer of rim tape . Im know expert so I presume then that it is 2 layers , it is very thin . I have had no issues .

Been riding mine all year. Tubed. PR3's at about 90/100psi. single strip of the narrow Stan's tape.

So far so good.

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dangerous curves ahead

A friend of mine experienced it. Going uphill, probably 20 kph. 20-23 degrees Celsius.





The rims had seen approximately 3000 km.

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12 Canyon Aeroad CF 9.0 ETE
12 Canyon Ultimate AL
11 Cervélo P2

Looks like the wide tape... only one layer, or two? And it's a GP4000, also...

Did he say how long the tire had been mounted?

Mine both came off while riding... but on a level road at moderate speeds. I'd hate to experience this on a descent... could easily be fatal.

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formerly rruff...

Well, we were at least 600 km into our training camp. Maybe more. I don't think the tire had been off recently.


Funnily enough I experienced a similar blowout on the same camp. I was going down the steepest descent from the Pico de las Nieves on Gran Canaria when my front tire blew off. Fortunately I was able to safely stop. The rim was warm but not hot. I was riding butyl tubes and GP4000s on new Mavic Ksyrium Elites. Tires had been running perfectly for about 1000 km on the wheels when it happened. No signs of damage to the tire except for that which appeared on the sidewalls when it was ridden and braked on wo air.

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12 Canyon Aeroad CF 9.0 ETE
12 Canyon Ultimate AL
11 Cervélo P2

djm,
your photos look like a thin/worn sidewall that has given way, leading to the blowout. i think the OP is talking about a blowout with no visible rim damage.
i used to have an old mavic MA40 that had this issue. never did find the reason, but it was more than 10 years ago. nothing recently, but i havent had that many alpha340s come through.