robo

I posted this on MTBR too.. sort of a 'don't be stupid like me' public service announcement:

I'm not sure if others use this weight saving 'trick', but i sometimes would run small (ie. 26x1.5) tubes, overinflated in my tires (1.95"), thinking it would save a bit of rotational weight, and that the tubes would probably be fine getting a little overinflated.

I guess not. I had some mysterious punctures on my front wheel, one of which almost caused a crash on a rocky descent, but i thought they were freak punctures, and just patched them and kept riding. This morning, i discovered that my front wheel had gone flat overnight. I took out the tube, and saw that one of the glueless patches had leaked, so i re-patched it, reinstalled it, and began pumping it up. When i got to about 40psi, there was a deafening bang (my left ear is still buzzing, 20 minutes later), a cloud of talc, and my tube had literally exploded, taking with it some of the kevlar tire bead. My precious vintage Specialized Ground Control tire is ruined.






In retrospect, the previous mysterious flats should have been a warning sign, but i had been using this 'trick' for so long that i never thought it was the culprit. Also, the glueless patch probably leaked because it the butyl tube was probably stretching out too much under it. I should note that this blowout did not occur where there was a patch, but in another place on the tube.

Anyway, just thought i'd pass on the warning. Use the proper sized inner tubes!!


I was just lucky this happened while the bike was on the work-stand, not while riding! (i wouldn't be deaf, but i might have gotten a broken neck and tacoed front wheel)

-robin

supcom

The blowout was almost certainly caused by pinching a bit of tube between the rim and the tire, not from running a small tube.

bwinton

I'm new to this sort of thing, but wouldn't running a small tube increase the chances of that sort of pinching?

robo

I doubt the pinching thing. The tire was kevlar beaded and very old (12 years), so it was quite loose on the rim (no tire levers needed for install/removal, actually). Also, i partially inflated the tube and popped it in, so i think pinching is unlikely.

Another possible explanation is the fact that this wheel has no rim strip (it came that way from JensonUSA). While i can't find any sharp edges, it's possible the tube got punctured from inside, but even then, it doesn't explain the explosive nature of the failure.

robo

Ah.. a bunch of people on MTBR are telling me it was probably the lack of a rim strip and the old tire (bead failure) that caused the explosion, not the overstretched tube.

womble

I did this for a while, only because I was new to biking and didn't even realise tubes came in different widths. In hindsight, it's bleedin' obvious that a narrow tube in a wide tyre is going to be overinflated and prone to failure.

bkrownd

The LBS here swears that tube "size" doesn't matter much, since it's contained within the tire/rim. Anyhow, no rim strip is asking for trouble. You're supposed to install the rim strip yourself, which is why they sell them.

Bikepacker67

I love it!

Working on your bike, on the hardwood floors....
Now that's a guy who's got his priorities straight!

Bikepacker67

Well... I see that the decline of civilization is right on schedule....

Disrespect for another's property is right up there with sex outside of marriage.

michaelnel

12 year old tire
undersize tube
patches
no rim strip

I think you should probably just stay home, you're a danger to yourself.

michaelnel

12 year old tire
undersize tube
patches
no rim strip

I think you should probably just stay home, you're a danger to yourself.

recursive

Pfffff.. I've had some bad landlords before. If they don't give a crap about their own property, why should the tenants?

Bikepacker67

No one is twisting your arm to live there.

robo

Well, thanks for the snarky comments, guys. I posted this in good faith thinking it might save someone else a blowout, but whatever.

Yeah, i live in a ****** NY apartment. If you'd like to provide me with a garage to work on my bike in, i'll be right over. Until then, it's my room or nothing.

The hardwood floors have survived 100 years of abuse, including about 600 sloppy coatings of lacquer/poly applied by apathetic supers.

And i do have that plastic sheet that you can see under the drive train, where oil actually does hit the floor.

recursive

Yeah, no crap. That's why I don't live there anymore. But around here, you have to sign a 1 year contract to get a place.

Bikepacker67

I wasn't being snarky - I assumed it was YOUR house, and thought it cool that you didn't have that annoying "Felix" attitude about what's important (replacing a sketchy BB) opposed to what's not (habitat accoutrements)

crank'n

two problems,
glue-less patches.
patches don't stick to talc powder on tubes.

robo

^^ I usually carry some alcohol prep wipes for cleaning the tubes prior to patching, but the last flat i got was on the trail and the last wipe i had turned out to have had a punctured package and it was dry.

CRUM

In my career in a bike shop I have mounted umpteen thousands of tires. From your description, it sounds like you did not check to see if the bead of the tire was properly engaged before pumping her up to full tilt boogie. I do not often have this happen to me anymore, but occaisionally I still get caught being stupid.

One safety hint - never inflate a tire with it between your legs. The boys will often take a hard shot when that tire decides to let go. And you will drop like a rock.

My tire mounting method
~Once you have the tube and tire on the rim, inflate it to the point where you can still squeeze the tire and manipulate the side walls(About 10 to 15 PSI).
~Work the sidewalls back and forth all the way around the tire.
~Spin the tire and look at where the tire meets the rim. Does it form a clean circle as it spins? Or is there one section that seems to bulge. The bulge generally means the bead is not set. Push the tire in. Work it back and forth.
~Inflate some more and spin the tire again.
~If everything is cool, run her up to the desired pressure.

This technique may seem over the top but it is not. I can swap most ATB tubes out in 2 to 3 minutes using this method.

phidauex

Sooo... Not a big deal? Thats refreshing to know.

catatonic

They are right....go get either a rim strip or some rim tape. Since it seems you care about this bike I'd go with tape...Zefal is good and relatively inexpensive.

nycm'er

I repaired my bike on my hardwood floor and had sex outside of marriage, and it's only 9:45 am: never thought those two pastimes would be paired; I'm glad I fit in somewhere.