It had turned into a great day. *After about 55 miles into my 95 mi..
trip I had a slight wind pushing me along and I was going to make some
time. *The asphalt had buckled against the expansion joints but no
need to slow down or swerve. *I was double tubed.

The first bad bump was about 5" above the bridge deck. *The front
wheel came down not quiet properly aligned with the direction of
motion and the water bottle flew out. *I recovered the water bottle
and quickly resumed riding in the same fashion. *A mile later the same
happened again except with a softer bounce. *The water bottle stayed
put. *The front tire was definitely softer than when I started out. *I
thought, finally an opportunity to ride on one tube but it quickly
became clear that _both_ tubes had pinch flat punctures.

This brought up one advantage of double tubing. *If the innertube
rubber is pretty thick and if you shift as much weight as possible to
the back wheel, you can more or less ride on the flat tire for short
distances.

I'll check to see if the punctures on each tube are side by side
indicating that both pinch flats happened on the same bump.

If not then the usage other cyclists have been recommending may hold.
Once one tube goes down then inflate the other tube, at least on
longer trips.

Two punctures lined up, side by side, but a shard of glass still in
the tire indicated it wasn't a pinch flat over one bad bump. *It
wouldn't have been a likely scenario for me to get the glass out
before the 2nd tube went down.

Tire pressure needs to be monitored more closely. This is very easy.

it's not really likely that any sharp will not puncture both in a very
short space of time.

It depends on several factors, the locations of most punctures on the
tire, the size of the tires and the location of the "seam" between the
two tubes, the puncturing object, pinch flats, riding style.

Obviously a larger tire presents a larger target so a typical
puncturing object will tend to be further away from the seam.

which kind of begs the question whats the point?

R & D. It'll take a at least 10,000 miles to get an idea and that's
deliberately swerving for glass, thorns, etc.

The Titantic was a good idea. The owners just didn't do enough
research before they declared, at least in their minds, that it was
unsinkable. My mistake wasn't nearly as bad because, after all, I
never really stopped. I just dropped my speed to 12 mph.

What's really curious is the 2 tubes only leak in two places each
after 33 miles of rim riding.

Sorry but I really can't see this being anything but a solution looking
for a problem.

There's no such thing as one solution.

tubeless tyres seem to be catching on slowly or simply robust tyres.

I like to ride tires down to the fabric. Personal transportation
should cost less than 0.03 cents/mile.

The biggest advantage of double tubing may be the ability to ride on
two flattened tubes without damaging the tire casing. Usually when an
under inflated tire hits a pot hole or is ridden on the rim and then
is re inflated to full pressure the belts rip diagonally and the tire
becomes too lumpy for a smooth ride. Yesterday I pumped the tire --
single tubed -- up to 50 psi yesterday with no problems after riding a
few miles. I just pumped it up to 65 psi and will try that for a 30
mile in a few minutes. I'll then try 80 then 90 psi, the rated
pressure, to see if double tubing saved the tire.

Part of the protection is due to the extra rubber from 2 tubes but
most of it is the tubes don't bunch up. The tubes are glued together
and pegged in two places instead of one by the valve stems. Both 700
c / 27" tubes are thin wall ~ 125 gms.


Roger
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