bdcheung

(x-posted to CX forum)

I was riding my CX bike to work this morning, riding it along the packed-dirt trail that parallels the asphalt MUP.

As I'm riding I hear a "thud thud thud thud thud thud BOOM" with the boom being my rear tire going flat.

here's what the tube looks like:


Any idea what could have caused this?

Tires are 700x35 Maxxis Locusts. Wheels are Soul S4.0. Tubes are Bontrager 700x35-44c

Jynx

An explosion like that I would guess is the tire slipped off the bead and the tube blew out the side. Have you recently changed the tires or that tube?

bdcheung

Nope, and the pressure was at 75psi this morning when I pumped it up. Seems like that would be plenty to keep the bead on the rim.

cyclewolf

With the thud, thud, thud, boom description I think it sounds like the tire lost it's bead. The thud, thud is the tube coming through the lost bead and then the boom being the subsequent tube destruction.

bdcheung

hmm

so what's the solution? Different rims? Narrower tire? Higher pressure?

Jynx

Exactly

A hole that big wouldn't happen inside the small area inside a tire.

waterrockets 

My bet: Your tube was slightly under the bead when inflated. Through the ride, it slowly pushed the bead off the rim. The air really wanted out of there.

When installing a tire, after both beads are on, it's important to push the tire away from each rim wall, all the way around, and ensure that you see nothing but rim tape down there. If you see tube, it's going to blow.

You'll get to where you know when you screwed it up without even looking. Usually, I fix it by inflating to about 15 psi and working that part of the tire back and forth until the tube finds its way up in there.

Jynx

Put a new tube and mount it up and you should be good.

I had something similar happen. I changed the tube after a flat. I keep my bike in my room fairly close to my bed. At like 3 in the morning there was a BOOM! Scared the crap out of everyone in my house. Rear tire was off the bead and the tube was blown out the side. I didn't make sure the tube was fully covered by the tire. Put a new tube in and have been fine since (about 4 months ago).

bdcheung

good to know, and thanks everyone for the responses.

To bring the story to a close, I didn't have a replacement tube with me (my "emergency" pack has 700x23 tubes. d'oh!) and ended up hitchhiking to my office. Quite the start to my morning.

Jynx

I would have just used the 700x23c. The worst is when you blow out a tube and only carry patches.

grolby

Now you know for next time: you can use a 700x23 tube in a CX tire and get away with it. Tubes are really, REALLY stretchy. I would change the tube once I got a chance, but I wouldn't hesitate to use the 700x23 tube in a pinch.

bdcheung

another thing that's good to know!

Brian Ratliff

FWIW, I've had a 23mm tire slip off the rim and blow the tube like that. It happened on an open pro rim (these seem to have a slightly undersized rim diameter) after I rolled over a crack or something which caught the tire and pulled it off.

I also had the bead slip with a cross tire during a race, though the tube didn't blow on that occasion even though I raced a lap and a half with it in that condition.

StanSeven

I do this too. Unfortunately I discovered it myself instead after a couple flats instead of having someone tell me.

MDcatV

this would be my guess

do tell about the hitchhiking ... stories like this are either the beginning of a porno or a horror flick.

bdcheung

you really want to hear about the Nigerian fella and his tinted-out ford explorer?

MDcatV

you're still typing, so no horror flick ... and no, if it's the other, keep it to yourself

Homebrew01

Yup. When installing tubes, it's good to have a bit of air in them. it gives them some shape and makes it less likely for them to get hung up. For non-foldable tires, I always put a few psi in the tube, then put the tube inside the tire first, then mount them both at the same time. Easier & less likely to get pinched tubes. You can sometimes do this with foldables after they've been used and hold a round shape better.

bdcheung

Thanks for the tips!

botto 

i imagined that you'd be something more than a copy boy.

bdcheung

Red herring.

BlastRadius

75psi may be too high, even for asphalt. That may be enough to blow the bead off the rim. I'm 133# and for asphalt I use 60psi in the rear and 55psi in front.

grolby

No.

Phantoj

I had a bead pop out and tire blow in a MTB race; I think it was after a minor wreck. Thud-thud-thud-BOOM and all that.

Psimet2001 

Not to be a broken record but that failure - long gaping ripping hole along the side of the tube - is directly indicitive of a blow out - tube becoming unrestrained by the tire and then expanding to the point of failure under it's pressure. Usually due to overinflation or, like in this case, improper mounting or bead seating.

This is almost always due to mounting technique or something that went wrong during mounting. No biggie. The "thump, thump, thump" before the gunshot is the telltale sign as well. That thumping is the expanding tube hitting the stays as the wheel rotates.

Tube failures are pretty easy to diagnose.

Put a new tube in and take care not to get the tube between the bead and the rim. Inflate a little and then rock the tire back and forth all the way around to ensure the tire bead is firmly seated in the rim before finishing the inflation.

BD - I know you already know this stuff - just kind of putting it here for others who may not.