Without Air Or Tubes, In 3D.

Three years ago, "The Retrogrouch" wrote about one of the most interesting and enigmatic companies in the cycling world.

Zeus probably came as close as any bike manufacturer to crafting all of the parts for its bicycles.  Of course, they didn't draw the frame tubes, which were usually Durifort, Vitus or Reynolds.  But they, or one of their subsidiaries did  make all of the other major parts, except for the tires.  But you could still ride Zeus tires on your Zeus bike.  How's that?, you ask.

Well, there was a company in the US called Zeus that made them. But they weren't the kind of rubber someone riding a Reynolds 531 frame with Zeus 2000 components would have wanted.  The appeal of that tire, the Zeus LCM, was found more among novice commuters and folks who didn't want to get their hands dirty or scratch their just-enameled nails. (I can understand that!)

Those tires were airless and didn't go flat because they were solid polyurethane rubber.  I tried them for a half-century and a few days of commuting. I wondered whether I had just experienced what it was like to ride a "boneshaker"!  

As so often happens when a new product comes to market, people think the idea is new when, of course, it isn't.  And when it disappears, it will probably return and have another generation of consumers believing they've just witnessed the most wondrous innovation.

Well, it turns out that the airless tire has been revived during the past few years.  Three and a half years ago, The Retrogrouch wrote about a new crop of such rim coverings. They were not solid, like the Zeus, but like other offerings that preceded them, they had solid inner tube-like inserts.  

Now a German startup company, ProFLEX, has created its own version.  This one does not have an insert but, unlike the Zeus, it is not solid rubber.  Instead, it is supported by a complex honeycomb-like structure inspired by a car tire Michelin introduced last year.  That network mimics alveolar structures like the air sacs of lungs:  solid on the inside and more flexible on the outside.  

(Or, since we're talking about Michelin here, we could say it's the inverse of a baguette, which is crunchy on the outside and chewy on the inside.)

The ProFLEX has one more thing in common with the Michelin tire:  It is 3D printed.

ProFLEX tire

Although I am not sure I would switch over to such tires, I would be curious to try them. I wonder whether their ride is more akin to that of pneumatic tires (most likely heavy ones) or solid tires like Zeus.

None of these airless tires, by the way, should be confused with tubeless tires, which are filled with air and can therefore be flatted.  I know:  Bill and I stopped to help a fellow who'd just been sidelined with his tubeless tires.  

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.

Letting The Air Out

Tubeless tires for bicycles have been available for about two decades.  I have never used them myself, but I understand how they are useful for some riders, particularly mountain bikers.  While most road cyclists' flats are the result of punctures from road debris, mountain bikers are more likely to incur pinch flats that result from riding tires at low pressures, which causes the tube to be squeezed between the ground and the rim. If I were to become an active mountain bike rider again, I just might try tubeless tires.

I once tried another product created with the aim of preventing flat tires. 

Imagine a (say, 27 inch or 700C) donut made from the kind of rubber used to make tire casings.  That "donut" is solid; it does not have a hollow core into which air can be pumped, let alone one that can accommodate a tube. 

As you can imagine, installing such a tire was not easy:  It didn't even have the "stretch" of a tight-fitting tubed tire with a particularly stiff bead.  (I thought it was difficult to put those old Specialized Turbo tires on Weinmann concave rims until I tried installing one of the solid tires I mentioned!)  Removing it wasn't easy, either. 

That tire--the Zeus LCM--was available for a few years from the late 1970's to the mid-1980's.  Frank, the proprietor of Highland Park (NJ) Cyclery, stocked a few only because a few customers wanted them.  He also kept a pair of wheels fitted with those tires so would-be customers could try them before committing.  During the time I was working at HPC, he allowed me to borrow them for a few of rides.

If I thought those tires were hard in my hands, they were even harder on the road. They felt like they were made of cement!  Believe it or not, I actually did a half-century, in addition to riding to and from work for a few days, on them.  Never before had I ridden so slowly and felt so banged-up after riding:  The Zeus tires lacked the buoyance of pneumatic tires.  I found myself wondering whether I had just experienced what riding on a "boneshaker" must have felt like!


By the way, those Zeus tires were made in the US and bore no relationship to the Basque/Spanish bicycle and bicycle component manufacturer. Ironically, the only items on Zeus bikes that weren't made by the company were--you guessed it--the tires (and, in the case of clinchers, tubes). 

Around the same time those Zeus tires were on the market, a few similar products were being made.  Also, at least one other company made and marketed a solid foam inner tube, and another made a closed-cell foam inner tube with a hollow core which, as Retrogrouch pointed out, was like a big elastomer.  They were even heavier, slower and harsher-riding than the Zeus donuts.

Those products apparently disappeared around the mid-to-late 1980s.  

Sometimes it seems that if an idea is silly, impractical or bad enough, its time will come, or come again.  (That could make Victor Hugo turn in his grave!)   So, would you be surprised to find out that someone is making closed-cell foam tire inserts  again?  For me, the only surprise is that one of the most respected tire makers--Hutchinson--is behind it.  They don't sell that insert alone, but as part of their "Serenity" tire, which is like one of their city tires (I forget the name of it ) with a tough casing. 

From the Tannus website

Knowing that, you also probably won't be surprised to know that another company--Tannus--is reviving the idea of the Zeus tire.  Like the Zeus, it's a fully-molded solid tire that come in an array of neon colors that would have sent even Valley Girls running and hiding.



As George Santayana said, those who ignore the past are doomed to repeat it.  The pneumatic tire is one of the most important inventions in the history of the human race, and certainly the most important bicycle-related inventions.  Without that chamber of air floating and cushioning the bike and its riders, the bicycle, most likely, still couldn't be faster than a horse, even with Eddy Mercx pedaling.