James <
james.e.steward@gmail.com> wrote:
I started using TPU inner tubes on my gravel bike a few months ago, and mostly without issue.
One pinch flat so far, that I repaired with a couple of drops of
Aquaseal glue.
A few days ago I swapped tyres on my gravel bike, from a new pair with
tread to an old pair that were a bit bald, but fine on our hard packed
gravel roads and bitumen.
Alas, the rear got a slow leak after a 40km ride.
I could not see any obvious damage to the tube, and it wasn't until I submerged the tube underwater that I found 3 imperceptible pinhole leaks where the tube would have been pressed against the rim tape.
The rim tape is factory installed on my Fulcrum Rapid Red 5 DB wheels,
and is in perfect condition.
I was able to repair the tube, again with a few drops of Aquaseal.
I suspect that when I installed the old tyre that somehow a few grains
of sand or grit became stuck to the rim tape or were on the tube, and
with 40 psi + pressing the tube against the grit, it caused a hole to form.
I just read a forum post from a person who suspects grit causing similar problems on his fat bike with TPU tubes.
I think regular butyl tubes would be far more capable of coping with a
grain of sand, given their additional thickness.
After patching, I cleaned the rim, rim tape and inside of the tyre case
with a slightly oily rag, to hopefully pick up any sand or grit prior to reassembly.
I've also found that if the rim tape has a whiff of lubrication from a
wipe with a slightly oily rag - and I mean a whiff - then it makes
seating a TR tyre on a hook bead TR rim with an inner tube, much easier.
My 45mm tyres will seat with 40 psi. It otherwise requires inflation
to near maximum pressure (60-70psi I think) to get the tyre to be seated properly on the rim. That can be an issue if you have a puncture out on
a ride and using a high volume low pressure pump for wide tyres.
That makes sense yes, the grit and the lube, in fairness I have double punctured once when I didn’t clean the grit out and did puncture if slowly
ie rideable just needed pumping every mile or so!
That was with a Butyl tube though equally I’ve changed tyres and found lots of dirt in the tyre which hadn’t cased issues on the MTB/Gravel bikes.
Roger Merriman
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