Self Sealing Inner Tube: Do They Work ?

On 4/17/2011 9:54 AM, David Scheidt wrote:
In rec.bicycles.tech Peter wrote:
:On 4/17/2011 5:01 AM, Tosspot wrote:
: On 17/04/11 09:27, Blue Heeler wrote:
:
: snip
:
: Cost to treat 4 tubes - about $26 made up of $20 green slime sealant,
: $2 scalpel $4 for 8 large tube patches. I guess there is also some glue
: in there too, but I buy my patch glue in bulk and still working my way
: through the 100 tubes I bought 5 years ago.
:
: Doesn't that stuff go off after a while? I tend to 'collect' glue tubes
: and have had a couple of *unopened* ones reveal themselves to be a solid
: rubbery block.
:
: Although, thinking about it, I've had some 5 year old ones be fine on
: first opening. Maybe it's in the manufacturing process.

:The problem is that the tubes are often not gas-tight. Since they
unopened) are sealed at the screw top end, the only place for them to
ass gas is at the bottom crimped end. What I do, even with new,
:unopened ones, is make another fold at the crimp. That seems to help. I
:also carry 2 glue tubes in my patch kit. In a gas-tight container the
:glue will last indefinitely.

You're repeating Jobst's 'this is how they did things in the dark
ages' spiel. Modern cement tubes are heat crimped. They're normally a
multi-layer sandwhich. It's not perfectly gas impermable, and some
are just defective, so there is a shelf life.

Perhaps, but my experience has been that some even recently purchased
tubes dry out for whatever reason. There's usually enough slack to
double over the tube at the crimp. I haven't had one dry out after doing
that, but I haven't exhaustively tested, either. When still-sealed tubes
dry out, it's obvious that it's the crimp that's at fault, either by
design or manufacture, doubling it up can only help.


For those who patch at the work bench, cement is available in larger
containers. An 8 oz jar with a brush in the lid costs a few bucks,
and lasts a long time[1], as ong as the cap is screwed on after use. If
it dries out, the usual cause is the solvent has evaporated; it can be
thinned with hexane. If it's over heated, it can vulcanize itself
into a blob.

[1] the tubes in a patch kit are 5 grams, so about 50 of them.


Unlike Jobst, I don't patch at the bench. I just don't have enough
flats. I've had perfectly good luck just patching on the trail/roadside,
which is my usual practice, weather and conditions permitting. I always
carry an extra tube or two and a patch kit with 2 tubes of cement. The
belt and suspenders approach takes little extra effort. I've found that
if I don't patch a flat immediately, I'll forget about it only to
rediscover it when my next one happens and the "good tube" happens to be
no so good. I haven't had Jobst's problems with failures of freshly
patched tubes, I just patch 'em and ride 'em.