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Two tubes in one tire - why not?(9 posts)

Two tubes in one tire - why not?Woof the dog
May 19, 2002 11:35 PM
i've heard some mtn.bikers doing that. They drill another rim hole for a second valve. I figure if someone would make tubes thinner than present, two of them could fit in and prevent a complete flat in a road tire. What do you guys think?

Sincerely

Woof.
because you were just asking how to take 12g off of a 512g wheelcollinsc
May 19, 2002 11:48 PM
you really want to throw another 90g on it?
Friction-that's whyAlexx
May 20, 2002 3:33 AM
2 tubes rubbing together are going to cause a lot of friction. Do you really want a blowout?
Nope.jw25
May 20, 2002 4:39 AM
The reason mt. bikers did this (I don't think many did, but I remember one GT pro - Gerd Schraner?) was to cut flat-changing time. One tube was left flat, and in case of a flat, they could just air up the spare and go.
While both could be aired up at the same time, reliability would drop. For one thing, you'd get lots of friction between the tubes, despite plenty of talc. And for another, each tube would be at half-pressure. In a road wheel, that means if one tube went, you'd only have 50-60 psi remaining, which probably wouldn't last long. Mountain is the same way - no way you could lose 20-25 psi and keep riding.
Plus, you're adding weight where it's least welcome, and with the plethora of CO2 inflators on the market, the time savings drop quite a bit.
Oh, okay, thanx!(nm)Woof
May 20, 2002 4:59 AM
nm
BZZZZT!!grzy
May 20, 2002 8:39 AM
Lots of people run their tires underinflated and 20 to 25 psi is no biggie on an MTB DEPENDING ON TERRAIN. If it's soft and loamy redwood forrest it works pretty well. Roling resistance is higher, but traction is superior, Denting a rim and a pinch flat are real issues. You can ride a road bike at 60 psi -but it's not recomended.

In actuality each tube would be at full pressure (120 psi), but when one went flat the VOLUME would suddenly double - so the pressure drop is actually a result not a cause (PV=nRT). Anyone who has studied thermo dynamics can relate. How is the friction between two tubes materially different than one tube and the tire casing? You've got one tube that must do all of the deforming instead of splitting it between two tubes. In reality the inner tube rubber just expands and contracts to accomdate the casing deformation - the tube doesn't really move or migrate in one direction as the tire rolls. Relative motion between the tubes isn't an issue.

Ther real issue is that it's damn hard to stuff two tubes in a 23 mm tire casing - even getting a Mr. Tuffy in can be a challenge. Going to even thinner tubes is a bad idea from a reliability standpoint.
BZZZZT!!Woof
May 20, 2002 11:05 AM
uh huh, so there is no big issue with friction after all, eh?

If you simply make the tubes a little bit smaller in diameter, i bet you could stuff it all in.

Sincerely

Wood the fog
Two tires on one wheel, now THAT helps!speedisgood
May 20, 2002 9:24 AM
It's like having a super Mr. Tuffy! Cut the beads off a used tire and stuff it in between the tube and outer tire. Makes the ride harsher, but I feel better having the extra flat protection.
get some Conti Gatorskin tires and no problem nmDougSloan
May 20, 2002 9:57 AM