02 February 2016

A Tube That Pumps Itself

Yesterday I wrote about airless bicycle tires.  The Zeus LCM tires I tried about thirty years ago made my bike about as quick as a donkey cart and gave it the handling of a shopping cart.  And, from what I read, it actually did less to deaden a bike's performance than other airless tires available at that time (about 30 to 35 years ago).  So it was no surprise that they all but disappeared a few years later.

I've been around long enough not to be surprised that there are attempts to revive the idea.  The new airless tires, and the insert made by Hutchinson, all have, from what I understand, the same drawbacks as the old airless tires:  a large increase in rotating weight (especially on road bikes), a hard, dead feel and difficulty of installation and removal.

Companies and individuals are reviving the idea because of people's fear of getting--or, more precisely, getting their hands dirty in fixing-- them.  When people learn that I ride bikes, the most common question is, "What do you do about flats?" While, in my mind, my younger, snarky self is saying, "I wear them when I'm not wearing my heels," I explain that fixing a flat is not a complicated process and that I carry a little vial of waterless hand cleaner if I'm going to work or some other place where I have to be presentable.

 When I've worked in bike shops, led rides and volunteered with organizations like American Youth Hostels and Recycle-A-Bicycle, I've told people that the one bike repair they should all learn is how to fix a flat.  I've also told them that if they do no other bike maintenance, they should keep their chains lubed and their tires properly inflated. 

Someone who's afraid to fix a flat also probably won't pump his or her tires if they're not obviously flat.  I think that people don't realize that all tires "exhale" air, and that such gradual air losses are less noticeably in car tires because it's less noticeable, given the greater volume of air.  They might go weeks or even longer before inflating their car tires, but probably need to inflate bike tires every week or two.

Then, of course--as with fixing flats and other bike maintenance--there are those who are too lazy or scared to do it.

For them, there is inventor Benjamin Krempel's creation, called the PumpTube.

A cutaway diagram of the Pump Tube.  The beige element represents the pumping mechanism.  From Gizmag.

It consists of a regular inner tube with a one-way valve in the valve stem. That valve draws in air which doesn't go directly into the main body of the inner tube. Instead, the air goes into one end of a tube-like pumping mechanism, which runs along the outside perimeter of the inner tube.  As the tire rolls along the ground or street, the pumping mechanism is compressed, which forces air into the inner tube.  The resulting absence of air in the pumping mechanism creates a vacuum effect, drawing more air into the valve. 

I should also mention that there is a dial on the valve stem that can be used to set the "target" pressure.  Once that pressure is reached, no more air is pulled in.

The mechanism in the PumpTube is probably useful in compensating for normal seepage or to counteract pinhole leaks.  Krempel admits that a larger punctures would  probably need to be repaired.

It will be interesting to see whether the PumpTube is actually helpful, especially to commuters and other utility cyclists.   If nothing else, it does overcome--somewhat--a drawback of one of Krempel's earlier inventions, the PumpTires.  As you may have guessed, it was a tire that had the same sort of mechanism as the PumpTube.  The problem with the PumpTire--aside from the fact that it requires users to give up their regular tires--is that once the tire tread wears away, the pumping mechanism is compromised. 

Plans call for Pump Tubes to be compatible with regular 700 C and 26 inch tires. Krempel says that once he perfects the design, he plans to start a Kickstarter campaign to produce PumpTubes, which are expected to sell for US $30 to $55 per unit.


  1. I enjoy your blog, probably because it spans some of my bicycle history, and notably because it is written with intelligence and insight.

    Your last two blogs focus on tires reminded me that the greatest difference I have experienced between bikes centered on tires.
    In the early 60's, I was a college student in rural Indiana, where no young adult rode a bicycle. My former roommate from Nigeria did buy a $10 bike and regularly rode past me walking to class with the greeting, "mechanical advantage." In any case, after destroying the Saab that my wife had bought, I decided that we should ride bicycles. The local hardware/bicycle dealer could only display derailler
    equipped bikes in a catalog. A Varsity looked very much like a Paramount, and he had never sold a multi-speed bike. The price difference was striking,
    and I ordered two Varsity...what is the plural?

    A couple of years later, living in Boston, I read in the Globe that there were bicycle races for adults.
    I went to a training race with my Varsity, and must say that the participants were tolerant of this ignorant guy. They even suggested putting on toe clips, practicing at 100 rpm, and returning to learn the game.

    Finally, I get to the "tires." A few months later, I traded the Varsity for a Frejus. I bought the $125 model 'cause I couldn't afford the $175 all Campy version. For $125 I did get racing geometry and alloy rims with tubulars...what a difference! I loved that bike for several years until it was stolen. That led to a PX10, but the difference was subtle.

  2. Anon: I loved reading your comment. It reminded me that we all, when we first started our journeys as cyclists, thought that "a Varsity looked very much like a Paramount." That's how they look to most people--unless, of course, they are bitten with the cycling bug, as we are.

    $175 for an all-Campy bike? These days, I don't think you can get a Campy cassette for that much!

    Ahh, yes, the PX10. That brings back memories.

    I must say, I haven't ridden a tubular tire in years. But I, like you, can still remember when you had to ride them if you wanted to go faster than walking speed.

    Thanks for your comment!

  3. Quite frankly, a "Bicycle tube that pumps itself" sounds like the title of a cartoon by Rube Goldberg.


  4. Leo--You're right! I don't think I'll ever buy that tube, but it was fun to look at it.