wtandem

Descending, about 40 mph, near our house at the start of todays ride, our front tire blew. We did not go down, thus lucky. It is a 700x25c Continental Grand Prix. Looks like it is a tire defect. Horizontal split, just above the bead, almost invisible till you start pumping it up. Either slightly below the rim or close enough that I am pretty certain nothing cut it. The inside just looks like the cords separated. I still had plenty of tread left. We are riding a 2013 Calfee Tetra with 404 Firecrest Zipps. I run the tire at 90 psi and had not used the brakes, so there were certainly no heat problems. 90 psi is well below the max rating on the sidewalls of 120. I am thinking it is time to switch tire brands. Anyone have experience with the new Pirelli tires? Anyone measure their width mounted on 404 Zipps ( a few years old ). I can only fit a 700x23c on the back of the Calfee and some tires a 700x25c is too wide for the front (used to use Michelins till I decided to go wider than 23c. Michelin 25c do not fit in the front).

wtandem

Typo, Calfee is 2003, not 2013.

merlinextraligh

I've had Continental 4000's fail at that spot on both singles and tandems. However, I don't think the risk is unique to Continentals, and any lightweight racing tire can fail like that. How old were the tires? The casing threads can fail before the tread is worn out, particularly if the tires have some age on them.

Your failure might have been age related, road hazard, manufacturing defect, or a combination. I think all you can do is inspect the tires regularly, replace frequently, and/or go to a more robust, heavier tire.

wtandem

The tire was about 5 months. I was thinking maybe age and replacing before the wear indicators show replacement. I switched from Michelin to Continentals maybe 5 or 6 years ago so I could get 700x25c on the front. This was the first failure.

gcb

I've had three sidewall cut/failures just above the bead as you describe. I found a statement on the Continental website warning that the internal hook (where the bead seats) on some carbon rims can be sharp and that these sharp-edged rim flanges can slit a tire sidewall. I checked the rim hook/flange on my carbon rims and sure enough they were quite sharp! I tried to post photos, but was blocked as apparently you must have at least 10 posts prior to posting photos and I do not have even 10 prior posts. If you happen to check your rim hooks I'd be curious to know if they are sharp.

wtandem

I did go out and check the area of the failure. They do not seem very sharp. These are Zipp Firecrest 404 are yours also Zipps?

gcb

No, they are not Zipp, but it is my understanding that the issue was not isolated to one manufacturer.

Monoborracho

I thought the recommended specs for the Grand Prix, and there are several types (4-Season, 5000, Classic) has minimum inflation of 95 psi or more. 90 psi seems like a very low pressure for a 25mm on a tandem. At a lower pressure is it possible that you had the equivalent of a "snake bite", only it bit the tire also? Cut near the rim? Was the tube blown at the same place?

I don't know your team weight, but we run 90 psi in our 32mm Conti Gatorskins.

I have no experience with the Pirelli tires so no advise there.

wtandem

I got the 120 psi max directly from the sidewall. It does not look like a snakebite and the hole in the tube matched the slit in the tire. It blew on a relatively smooth part of the road. Our team weight is about 265 lbs.

Carbonfiberboy 

We run 95 psi on Conti 4000 IIs 28mm tires, measuring 32mm inflated. On 25mm tires, we ran 115 psi. To run a pressure equivalent to our current Conti 4000IIs, one would have to run 120. Our team weight is 282 lbs.

We've been running Contis of one sort or another for over 20 years and never had a sidewall failure. As said above, sidewall failures happen to all brands, but they are very rare.

Conti 5000 25mm tires have a max pressure of 123 psi. That sounds like a good tire for you. I've been told that the 5000 series are more true to size than the 4000 IIs series, which ran big, though I have a 23mm Conti 5000 on my road bike with 23 mm outside rims, and it measures 25.8mm inflated. The wide rim will make some difference.

Building a tandem that can only take 23mm tires is a little odd. That said, I have friends who own a relatively new Calfee Dragonfly. They won their AG at Nationals on 23mm tires inflated to 140 psi. IIRC, they were running Vredestein Tricomp tires with a sidewall max of 170. They don't make that tire anymore, but Vredestein's Senso Superiore 25mm has a max pressure of 145. Several other tires in their lineup also have a max pressure of 130 in 25mm, and might be a good choice at 115-120 psi.

mikebian 

In July, I bought a pair of GP 5000 28mm tires for our Calfee. We run them with 100 PSI on a set of Rolf tandem rims.

With about 250 miles on them, we were climbing a big hill very slowly and the rear tire blew out. There was no pothole or rock or anything. We were going maybe 5-6 MPH and there was a loud pop as the tube blew out. The rubber on the tire bead came apart. Fortunately, we always carry a spare tire and we were able to complete the ride.

I tried writing to Continental, but I got no response from them. It's nearly impossible to figure out how to make a warranty claim on a bike tire on their site so I just wrote to their general email address. There was no phone number to be found. I bought the tires from BikeTiresDirect.com, so I wrote to them asking for a phone number or email to make a claim to Continental. They quickly replied that they would send me a new tire, and a few days later, I got it in the mail. I really like BTD! Never heard anything back from Continental.

Haven't had any issues since and we have about 2,000 miles on them now. With our business temporarily shut down (Adventures In Tandem) and nothing much else to do, we rode over 6,000 tandem miles this year, a new record for us.

wtandem

In 2003, my local dealer convinced me to order 130 mm spacing and I did not think to ask about tire size. It was before the move to wider tires and lower pressures. We have had no problems with standard road spacing on the wheels and as he suggested it allows for a wide choice of hubs/wheels, but I do wish I had thought about wider tire accommodation. Greg, the local dealer, was a nice guy, let us take home his Calfee Tetra with a Campy double, to test ride over the weekend. It was an easy decision after weekend rides with my 8-year old son and wife. On our Co-Motion travel tandem, we run 28 mm tires. On our 1976 Jack Taylor, I put 32 mm Gator Skins for l’Eroica in California.

Carbonfiberboy 

That bottom photo is very interesting. Some years ago, there was a thread here about running reflective sidewalls for better night visibility. The photos were quite striking. They were Conti 4000 IIRC, not the later IIs. The reflective sidewalls looked very much like your bottom photo, exposed fabric with some sort of reflectivity in it. Though I assume that yours aren't reflective, they look similar. I blew two of those tires off the rim during short, steep descents, rim brakes of course. That had never happened before or has happened since. I did the same with Conti as you did, no response, but those reflective sidewalls disappeared off the website. I gather I wasn't the one one to have had a problem with them.

I checked my stock of 5000s. I have 23mm, 28mm, and 32mm and none of them have fabric visible there. All the fabric is covered with rubber in the normal fashion. Your tire didn't actually blow out, as I understand that term, rather it blew off the rim, just like mine did. The rubber on the tire bead was peeled off by the rim bead. My guess is that the fabric does not hold to the rim bead as well as rubber does, less friction, so it's more apt to blow off. Yours peeled the rubber off the bead, though mine did not.

So if anyone else here ever gets a Conti tire with fabric showing there, replace it.

wtandem

I am pretty sure our tire from the original post did not blow off. It was still well on the rim when we stopped. He is a picture of our failure, a very similar spot to the picture you are referencing, although not nearly as large.

Carbonfiberboy 

Right, even more interesting. Your tire has that same fabric showing right above the bead as the blown-off tire has. I went out and deflated our 28mm 5000 which we've had on the front for several months, enough to wear the flashing off and start to develop a flat in the center. The area right above the bead looks just like that same area does on my in-the-box 5000 tires. If you have any others, you should take a look at them, see what that area looks like on them.

I wonder if it's the 90 psi? The official pressure range for a 25 is 95-123 psi. Back when I ran 25mm, I ran them at 115 Should have used 120, but that was just too harsh. I wonder if running them under-inflated and under much heavier than usual load, caused them to move a tiny bit at the bead and saw away at that area until the rim went through. That's what it looks like.

I'm running my 28mm 5000 on the front, which measures 29mm inflated on my rim, at 105psi. I run 32mm tires on our tandem at 95 lbs. 282 lb. team, 36 lb. bike. My rule of thumb for our tandem is tire pressure = 3000/(measured tire width). Because of tandem frame design and the usual proportion of captain-stoker weight, tire pressures on both ends are usually the same, unlike a single.

reburns

What model and vintage is that Continental tire? I’m curious, because that sidewall molded detail looks familiar but I don’t see it on any of the models in my garage, including gp4000, 5000, 4 seasons or gatorskins. I’m also noticing a line of what looks like circumferential cracking up near or on the tread area. Could that be due to running under inflated? If so, that could have possibly also put wear and stress on the interface between tire and rim, where the split occurred.

FWIW, I’m running 32 mm GP 5000 front, 32 mm 4 seasons rear. They measure 34 mm on my rims and I inflate them to low 80s front, high 80s rear. I stopped using GP 4000/5000 on the rear due to the frequency of sidewall cuts and dings back there. Total team, bike and gear weight approximately 350 lbs.

gcb

I remembered that I had save a couple links discussing the potential for some carbon rim hooks to eventually cut through a sidewall just above the bead. Thought I'd post the links as they may be of interest to others.

Article by Lennard Zinn: velonews.com/gear/technical-faq-a-tubeless-tire-blowout-in-the-pyrenees/

Warning posted on Continental website: conti-tyres.co.uk/tyre-bead-seating-on-carbon-clincher-rims

wtandem

They are Continental Grand Prix, pretty recent vintage. https://www.continental-tires.com/bi...res/grand-prix

I decided to try these as slightly heavier, but maybe tougher than the 4000, I had been using.

wtandem

Wow, very convincing article by Leonard Zinn, I will at least look into sanding the hooks on my Zipps before riding them again. I suspect my rims are not too bad since I have had several sets of tires on them over several years and never had the problem before, but we are too old for the risk. Thanks for finding this.

Carbonfiberboy 

OK, not in the 4000-5000 series. Do note that the minimum tire pressure for those 25mm tires is 110 lbs. and you are in a tandem.
https://www.continental-tires.com/bi...res/grand-prix
Do not inflate them to less than 115! No mystery here. Manufacturers' tire pressure recs are for good reason and only they know what that is.

DangerousDanR

This is a GP5000 tubeless 25 mm tire. I had this tire failure on my solo bike. Rolf alloy wheels, so no blaming the carbon rims. This was the rear tire, and it had about 2000 miles on the clock. I believe this happened immediately after hitting a steel bridge to shore junction. Fairly low speed, rear wheel. Pressure was probably 90psi or so. I still have GP 5000 on my road bike and on our tandem. But I take a close look at the tires once a week just because this would have hurt if the speed had been greater.

dwmckee

This was my thought as well. The pressure is pretty low for a tire of that width on a tandem. There could have been a rolling pinch flat damage that could weaken the casing for a long cut just above the rim.

Also, tire defects are not all that rare among all of the brands. We had a batch of bad Schwalbes that blew off the rim (3 in a row) when were inflating new installations on a bike. All 3 went well below the recommended pressure. Schwalbe replaced all 3 with a phone call. Turned out there was a bad batch that many had and there was some buzz online about it for a while among the shops.

jnbrown

We used to use Conti 4K and had no problem with them.
But switched to Schwalbe One and ride is better and durability is as good if not better.

Chancy

Folks,
We experienced a similar failure to MikeBian's. I had just installed a 700x28mm (measures 30.4mm at 105 psi) Conti GP 4 Seasons on our rear wheel (Spinergy Z Lite rim). We had an identical tire on this rim for 2,100 miles with no problems. The new tire blew out while riding 16-17 mph on a flat pavement, no rocks, potholes, etc. The tire only had 39 miles on it when it blew. You can still see the mold "hairs" on it. I purchased several of these on sale from Plant X in the UK a couple of years ago and still have 2 left. I like Continentals and have used them in various widths and models for years and this is the first failure that wasn't caused by road conditions. Do you think it's safe to install another and go with it? I felt the "hook" portion of the rim and it doesn't feel sharp, plus a had an identical tire (from the same bulk order) on the rim for 2,100 mile trouble free.
Data: Team wt- 350 lbs; we ride only on pavement and don't corner too aggressively.




Tailwinds,
Charlie
2016 Santana Beyond

P.S. The rubber delaminated from the bead and the tube has a 1/2" slit matching that spot on the wheel.

Carbonfiberboy 

Are these the reflecting sidewall version of these tires? They look like it. I had 2 of those blow off my rims. Threw them away, wrote to Conti, they no longer make reflective sidewall models.