Bicycle Mechanics - Tire blew off of rim while in garage

While sitting in my living room I hear what sound like a gunshot coming from the garage. Uppon investigation I see the front tire blown off the front rim of my 2007 Cannondale touring bike. Rims are DT Swiss TK 7.1 with Schwalbe Marathon 700 x 35 tires. I keep them at 85 PS
There is no vilable damage to the rim and the tires have just over 1300 miles (tread still looks like new). Appearently the bead becam unseated.
Is there anything other than defective tires that would cause this to happen?

AL W

Most likely improperly mounted pinching the tube.

Tire was still mounted from when the bike was bought at the LBS. Never had a flat till now. When mounting the tire with a new tube it went back on the rim with very little effort, a lot easier than any other tire I have ever mounted.

Tire was still mounted from when the bike was bought at the LBS. Never had a flat till now. When mounting the tire with a new tube it went back on the rim with very little effort, a lot easier than any other tire I have ever mounted.

What does the tear on the tube look like?

Try a new tube and make doubly sure that it isn't pinched anywhere.

Schwalbe are crappy tires. Check the side wall and lip.

And by crappy, I mean falls apart prematurely.

I had the same happen with Schwalbe folding Marathon Supreme, 700x35 on Synergy Rim, very loose fit, the tire had been fine on another rim for 1/2yr but blew spontaneously after three days on the Synergy. The tube was shreaded along the rim side,,ie. in the middle of the rim. Consensus here was pinched tube but I'm not sure, I wonder if there was a bit of aluminum flashing poking through a marginal rim strip made of cheap duct tape. I've remounted with a new rim strip,tube and anxiously wait to see if it happens again, pumped to 80psi.

I keep them at 85 PSWho ever inflated the tires most recently, is responsible for the inspection of the tires' mounting and condition. If you were the last person to operate the bicycle and inflate the tires, the "blow off" is your responsibility.

Whether or not this event remains a mystery is anyone's guess.

the tire had been fine on another rim for 1/2yr but blew spontaneously

Interesting. The one time this happened to me it was with a tire that had been on another rim. I remounted it with a new tube, and it's been fine ever since.

Schwalbe are crappy tires. Check the side wall and lip.

And by crappy, I mean falls apart prematurely.

That's rubbish. I've been using Schwalbe tyres for years, and I have never had problems.

A pinched tube might take a while before it shows up as a problem. My dad recently crashed because of a front tube blowout while going down a hill. He had replaced the tube a few months ago and mistakenly put a 28-32mm tube in a 25mm tire. The extra rubber caused him to get the tube partially pinched near the valve stem and it blewout at a bad time.

My one and only flat on my commuting bike happened 7000 miles after installing the tires/tubes (tires lasted another 3000 miles before I finally replaced them and never once flatted because of a puncture). I had twisted the tube slightly during the install and over time, the rubber wore thin from rubbing against itself and eventually caused a hole.

Check the edge of the tire lip, VERY CLOSELY.

I had a tire one time that kept blowing tubes for no apparent reason, and finally determined that the edge of the tire, right at the bead, was "bent" or "creased" or "nicked" and was the reason.

That imperfection allowed the tire to work it's way off the edge of the rim at that exact spot, and it always blew the side of the tube out. The dealer even changed the tube a couple times, thinking I was doing something wrong.

My LBS gave me a new tire and it never happened again. He even gave me a half dozen tubes to replace all the tubes I bought from him.

The vast majority, like 99.9% of the causes of these spontaneous blow-outs are due to pinched tubes during tyre-mounting. Telltale signs of pinched-tube blowouts are HUGE rips in the tube. Typically star-shaped and towards the rim-side of the tube. Unless you've done the following, you cannot rule out an improperly installed tyre:

1. give tube 1-pump to form it into round shape instead of flat

2. if 1/2 tyre already mounted, push valve into rim and stuff tube into tyre

3. start pushing remainder of tyre over starting near valve-stem and go over valve-stem along the way (DO NOT save valve-stem area for last)

4. after tyre's installed, push the valve-stem into the tyre to ensure that tube in that area isn't pinched

5. after tyre's fully mounted, let out some air from tube so you can pull tyre sideways and look down into gap between tyre and rim-edge

6. look for pinched tube showing, then move over a couple inches and pull tyre sideways again and look

7. work your way around entire circumference of tyre, then inspect the other side all the way around

8. only after ensuring no tube is showing anywhere around entire tyre would you then pump up the tube.

Thanks Dannon for a good 'how to'. If I could only figure out what a 'tyre' is.

Number 1. up above is very important. Put just enough air in the tube to be able to feel it with your fingers as a tube. And gently work it up into the tire before you fully seat the second half of the clincher's edge up and over the rim.

I've had a cheap tube blow-up before in my garage one night. I was expecting the police! It went off like a 9mm. BANG!! LOL.

Thanks Dannon for a good 'how to'. If I could only figure out what a 'tyre' is.You're welcome and not everyone speaks American. ;)

Telltale signs of pinched-tube blowouts are HUGE rips in the tube. Typically star-shaped and towards the rim-side of the tube. .

you described it exactly

While sitting in my living room I hear what sound like a gunshot coming from the garage.

That happened to me but in my living room! I nearly S&*T myself it was so loud. Turned out that the kid at the LBS I bought it from 2 days earlier told me to keep the tires at 120lbs. Looking the the tire side it said 90lbs. I keep them at 90. Man it did indeed sound like a gunshot!

Was the tyre damaged when it blew? Typically the sidewall numbers are 1/2 of the actual pressure required to expand the tyre bead enough to blow it off the rim.

That's rubbish. I've been using Schwalbe tyres for years, and I have never had problems.

I've had six Schwalbes. 2 x 28 for a roadster, and two sets of EA3 26 inch tires. I bought them because I didn't want cheap tires on my commuter and they have reflective sidewalls. I liked them, so I threw them on two other lightly used bikes. Two have blown tubes out the _sidewalls_ and two had crumbling edges on the beads that blew the tires off the rims.

I'm glad you're having some luck with them, but I still think they are crappy tires. And, it sounded like this guy had the same problem.

Incidentally, please note, although my experience is the opposite of yours, I do not assume you are full of crap, er, rubbish.

Schwalbe are crappy tires. Check the side wall and lip.

And by crappy, I mean falls apart prematurely.

I've had zero problems with Schwalbes. My experience is limited to Marathon Slicks, Marathon Racers and Stelvios.

I've had zero problems with Schwalbes. My experience is limited to Marathon Slicks, Marathon Racers and Stelvios.

The 28s I had were Marathons. The 26s were Delta Crusiers.

If you'd posted like that in the first place, I would not have disagreed. Also, I only wanted to say that I disagreed with your blanket statement that Schwalbe tyres are crappy, not that you were crappy, or trashy, or rubbish :)

After four blowouts, and LBS telling me I put tube and tire on wrong or had snake bite. I tried brand new tires and tubes. One blew just 800 feet into ride, and another after one mile. Been riding bikes and mounting tires for 50 years so do have some experience. That makes 4 blowouts in 4 months.
Built a brand new front wheel, and no more blowouts! Am looking for cracks or other imperfections now on old rim. If LBS did not dismiss me out of hand thay might have been able to sell me a new wheel.
BTW riding with same tires that blew off, for quite a few miles now.

I had the same happen with Schwalbe folding Marathon Supreme, 700x35 on Synergy Rim, very loose fit, the tire had been fine on another rim for 1/2yr but blew spontaneously after three days on the Synergy.

That is strange. I've been riding 700x32 Supremes on Synergy's since last November.
They were very *tight* when I mounted them. I have had no problems whatsoever with them.
How long ago were those Synergy purchased? I'm wondering if Schwalbe changed the bead dimensions.

the synergy was purchased last fall. The Supreme is much looser than I'd prefer and about a year old. It's a folder. I've been running a Supreme on the rear and Pasela TG on the front,,ridden through glass a few times with no flats.

Was the tyre damaged when it blew? Typically the sidewall numbers are 1/2 of the actual pressure required to expand the tyre bead enough to blow it off the rim.

Where does that data come from? I hear that all the time but nobody has ever been able to give me a reliable source. If that's true, I'd think there would have to be a "standard" rim for testing bicycle tires.

Where does that data come from? I hear that all the time but nobody has ever been able to give me a reliable source. If that's true, I'd think there would have to be a "standard" rim for testing bicycle tires.It probably all started with the wizard himself: http://www.sheldonbrown.com/tires.html

"The legal department wants the number kept conservatively low, in case the tire gets mounted on a defective or otherwise loose fitting rim. They commonly shoot for half of the real blow-off pressure."

I would think that the only kind of rim that could be standardized on for testing is a straight-walled non-hook bead rim. That way, ALL of the slip-off resistance would have to come from the tyre-bead itself.

I've had zero problems with Schwalbes. My experience is limited to Marathon Slicks, Marathon Racers and Stelvios.

I've managed to destroy two Stelvios (on separate occasions) by riding over a pothole. They both broke in the same way: looking from the inside, the threads have been separated from each other at some point. Looking from the outside, at the same location, the entire tyre seems to have an S-shaped bend with maybe a quarter of an inch runout side-to-side. It's still rideable after that, but with a noticeable bounce at the damaged spot.

I'd be interested to know what Schwalbe does differently. No other tyre seems to break in this fashion.

It probably all started with the wizard himself: http://www.sheldonbrown.com/tires.html

"The legal department wants the number kept conservatively low, in case the tire gets mounted on a defective or otherwise loose fitting rim. They commonly shoot for half of the real blow-off pressure."

I would think that the only kind of rim that could be standardized on for testing is a straight-walled non-hook bead rim. That way, ALL of the slip-off resistance would have to come from the tyre-bead itself.

Unfortunately, there's no way to ask Sheldon where he heard it.

The non hook bead thing is what started me thinking. Back in those days tires were rated at around 75 or maybe 85 psi. NO WAY would they hold twice that. People would blow them off the rims with gas station air hoses all the time. For that matter, a hook bead tire on a straight sided rim probably isn't going to hold even it's rated pressure.

I wonder if it's true. The "twice the rated pressure" thing is something that I hear all the time and it has a ring of believeability. People obviously exceed tire psi rateings by 10% or 20% and suffer no consequences. Sheldon is certainly a pretty good source but he wasn't a tire manufacturer. If he got his information from a first hand source that would be one thing. If he was just repeating what he heard over the years because it has the "ring of believeability", that's something else.

If true I'd think there would be a written testing protocol floating around somewhere and I don't know how to look for it. It doesn't impact me personally because most bike tires are rated for more air pressure than I ever use. It's just one of those things that "everybody says" and I wonder if it's really true or if it's one of those urban legend things.

Hmmm, I got a couple of straight-sided rims in the garage here. Maybe I'll build up some wheels and test blowing off tyres with them. The old gumwall tyres for those rims were typically steel-beaded, so they can hold more pressure than the folding kevlar beads that became popular around the same time as hook-edge rims. Would be an interesting test... I suspect that the surface-friction of the tyre on rim-edge makes a difference of some sort as well...

Hmmm, I got a couple of straight-sided rims in the garage here. Maybe I'll build up some wheels and test blowing off tyres with them. The old gumwall tyres for those rims were typically steel-beaded, so they can hold more pressure than the folding kevlar beads that became popular around the same time as hook-edge rims. Would be an interesting test... I suspect that the surface-friction of the tyre on rim-edge makes a difference of some sort as well...

Is it even necessary to lace them onto hubs?

Wear ear plugs.

I've had the same experience with Schwalbes. Schwalbe Marathon Plus on Alex Rims. Not a good combo. Schwalbe Big Apples on Salsa Delgados.

Tight rims and loose tires go BOOM!!!!! But mounting the same tires on Sun rims and ... no problems.

Is it even necessary to lace them onto hubs?

Wear ear plugs.

It's more safe to say that the real blowoff pressure is quite a bit higher than what's usually labelled on the sidewall.

Where does that data come from? I hear that all the time but nobody has ever been able to give me a reliable source. If that's true, I'd think there would have to be a "standard" rim for testing bicycle tires.IIRC, it may be from a magazine article by Frank Berto. Unfortunately, I never saved it, and the only part I remember is a vague memory about the blowoff pressure being around double the recommended maximum on the sidewall.

Ghosts

Is it even necessary to lace them onto hubs?

Wear ear plugs.I've tried inflating tyre on bare rims. The pressure distorts the rim into a toroid shape well before you get to the max-pressure rating on the label; much less pop-off pressure.