Re: TPU inner tubes and sand or grit

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