Carbonfiberboy 

We have now blown 2 Conti 4000s tires off our rims. These are the ones with the reflective stripe. There was quite a discussion of that stripe on here a few months ago and we decided to buy four of them and give them a try ourselves. One tire succumbed to cuts in a few hundred miles. Its mounted mate blew off early in its life, but since the bead was destroyed I couldn't tell what the fault was. The second pair lasted long enough for us to wear about half the rubber off them. We always run 120 psi in these tires.

One rim was a Mavic CXP33, the other was a Velocity Aerohead. In both cases we were braking hard at the bottom of a terminal velocity descent. In both cases the rim was only warm to the touch. The first time was a front rim and the tire and rim were both destroyed. The second time, this past Sunday, it was the rear, which blew just as we came to a stop, so rim and tire were undamaged. We always carry a spare so we put that on and continued with no problem.

We have a friend who also blew a 4000 off her single this past May. She was sucking our wheel on a 30 mph easy descent and blew a rear tire off braking for the end of ride parking lot. Rim again only slightly warm. I don't know which model 4000 it was.

In all these cases, the tire had been mounted for several hundred miles, so it wasn't a mounting error, plus we are pretty good at mounting tires after changing few hundred flats.

Examining the tire, the bead shows frayed cloth on the surface in the bead groove and deteriorated rubber on the bead itself most of the way around the tire. I also removed the front tire and examined it. It also shows the beginnings of this same problem. The bead groove is mostly cloth and the bead itself is beginning to tear off.

I have four new regular 4000s 25c tires, purchased from PBK on that recently posted deal. I examined them and they seem to have a good layer of rubber over the cloth in the bead groove, though the weave of the cloth is visible through the rubber. On none of my other brands of tires is that cloth weave so close to the surface in the bead groove. I mounted a pair of these new tires and will keep a close eye on them.

My theory is that hard braking caused the tire to slip slightly on the rim because the metal of the rim bead was running on cloth rather than on rubber. This encouraged the bead to pull out of the rim.

I've emailed Conti about this and will post any response. Meanwhile, I'd encourage anyone running Conti 4000s tires to pull them off, examine the area of the bead, and post what they find.

ct-vt-trekker

We also had a 700x 25 Conti 4000 blow off the rim a few weeks ago. I think in our case I thought it was a defective tube because the tube was split about 9" to 12" long . The tube blow completely out of the rim adn wrapped around the cassette. We were able to come to a stop quickly but we did ride on the rim for a bit. But since you mentioned this I could have had a similar issue, unfortunatley I can't check our tire because I threw it away.
I switched back to 700 x 28 GP 4 seasons for the time being.
Thnaks for the info, I'll keep an eye on my Conti 4000s that we're still using on all of our single bikes.

Carbonfiberboy 

That's what the tube always looks like after a blow-off. Which variant of the 4000? One possible theory is that the extra weight of a tandem causes the rim to wear the already thin rubber off the bead area, exposing the cloth, and leading to a blow-off. I'd be interested in the appearance of this bead area on your singles, if you wouldn't mind having a look.

mibike

I have 4000s 25c tires on my single. I deflated them so I could see the bead area and took a good look at them. I could see no problem. I’ll keep an eye on them. I like 28c on the tandem so I run 4 Seasons on them. I have been told by Conti that a 4 Season is a 4000 with more flat protection. I took a look at them and see no problem. Based on your theory of the extra weight and if it’s correct that this is the same tire the width could be the difference. I run Dyad rims on the tandems so it’s also might be possible that the wider rim doesn’t cut into the tire as much.

ct-vt-trekker

Ours was the regular Continental 4000 not the "S". Then one that blow off the rim was the rea. I just looked a the tire that was on the front, this one was installed at the same time as the rear one that failed. I don't see any noticable wear along the bead area compared to a brand new 4000 tire that I have. There was no exposed cloth.

Carbonfiberboy 

I just took a closer look at my bad tires. They were marketed as the reflective sidewall version of the 4000s, but nowhere on them is there any tire model designation. They just have the Continental logo, Made in Germany, size, pressure, hooked rim warning, and rotation direction. I dug an old 4000s, a regular model that had sustained a cut, out of my spares bin. Its bead looks OK, though it only shows a few hundred miles wear.

jnbrown

I have been using those tires for a long time without a blow off or even a flat. The rear is almost completely worn.
It does make me uneasy to hear these reports.

tandem rider

About 10 years ago we blew the side walls on two Continentals within a few weeds and stopped using them. When the Gator Skins came out we went back to the Gators and have had good luck with them.

Carbonfiberboy 

Yes, that was a problem with the old Contis. I had the cords break in the carcass of a couple of 3000 tires. The 4000 series does not have this problem.

Carbonfiberboy 

I'd pop them off and look at the bead. If it looks normal, nice sharp crease in it from the rim, cloth not exposed, I wouldn't worry about it. OTOH . . .

I'm still running 4000s Contis, just not those with the reflective stripe. Or maybe I just had a bad run. I'm looking for more information from other Conti 4000 users.

gracehowler

We are also doing well with gatorskins. I have 4000's on my single with good success, but not much load on that one.
R

jnbrown

I just changed the GP4000 rear tire today.
It is the 25c with the reflective side wall.
The tread was almost completely worn and I would have left it on longer but we are starting a tour on Saturday.
I looked at the bead and there is exposed fabric around the entire tire.
The new tire has rubber or whatever it is covering the fabric.
I think it is normal for the rubber to wear off exposing the fabric and I don't believe this is an indicator that the tire will blow off.

zonatandem

About 25+ years ago when Contis first were imported experienced a front tire blowoff in a mass start lineup . . . Kaboom! . . . Wondered whose tire had exploded.
Oh . . . ours!
That's before the switch to kevlar beaded tires from wire beaded.
We've been using Maxxis Re-Fuse tires 700x25 for the past several years with excellent results on our Zona tandem.
Just our input.
Rudy and Kay/zonatandem