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Don't let me burst your balloon (tires).

Famed though I may be, as one with a talent for analyzing matters of an artistic or cultural manner, there are times when even a humanities snob like myself must deign to speak in empirical terms. Today, it is to dispel a myth going around that balloon tires are fast. If they could be pumped to 100psi without emulating the big bang, that would almost be true. But they can't, and neither would anyone want to do that, as the supposed reason for these tires' being, is to provide cushioning.

The term rolling resistance refers to the energy that goes into constantly massaging your normally convex tires into the flat surface they present to the road. A good solid 100 pounds per square inch (psi) will keep rolling resistance low, by reducing the size of the contact patch being massaged. Massaging one knot in your friend's back, by kneading hard with a thumb, takes less energy than massaging their whole back with both hands and your chest (we'll return to the question of which is more fun). The contact patch expands until equilibrium is achieved between the equal and opposite weight of your bum pushing back off the road, and the pressure pushing on the dark side of your rubber. If you and your bike weigh 200lbs, and that weight, for argument's sake, is shared evenly between both of the wheels, then a one-square-inch contact patch for each tire, inflated to 100psi, will establish this equilibrium of which I speak. Comprende amigo? One square inch of tire, with a weight of 100 pounds of air from behind, will oppose that 100 pound force of the road. [Ref. 1]

Now focus your thoughts on that inch square patch of rubber at the moment when the hard road is massaging it flat, and imagine all the tiny forces in those fibers of rubber. Hear them squelching, making sound energy. Feel them rubbing, generating some heat. Sound and heat are two forms of energy other than kinetic energy, the energy form you're trying to make from that your pasta you ate. You can reduce those stresses by using tires made from a soft compound rubber. However, such tires are more prone to punctures, and will wear out much quicker. Better still, pump your tires to 200psi (they, might not pop), and halve the size of that contact patch being massaged. The certain problem with this last approach, is your bike will feel like a tuning fork. Ever wonder why Lance Armstrong had troubles "down there"?

Balloon tires permit low inflation, and a super soft ride. Now the proud owner of a Velorbis Scrap Deluxe balloon bike, I've been doing the maths. Together, it and I weigh 200lbs, with roughly one third (66) of those pounds over the front wheel, and the other two thirds over the rear. 22psi in the front wheel feels just right to me, eliminating those jolts from the forks. Okay, sure, that leaves a whopping 3 inch square contact patch beneath the front tire (66/22=3), but it's a fairly localised patch, not insinuating sides walls into its dramas, as the diagram above kind of explains. Besides, I figure I will more than account for the rolling resistance on the unloaded front tire, when I inflate the hell out of the loaded up rear one, from which I don't require cushioning, because my bike has a sprung saddle and long slender seat stays.

But herein lies the rub: the max pressure rating for Fat Frank tires, is 60psi—balloon tires just don't go any higher. That means I still have a contact patch of 2.2 square inches beneath my rear tire, a tire from which I don't require dampening. 

I would say that's a fairly standard Balloon tire story these days, that would apply for Electra Townie bikes, Retro Velo models, and so on.. Contact patches might be local to the actual patch, but by racing bike standards they're triple size, and still double what they would be if we all just kept riding to work on our 1.5" commuting tires inflated to 85psi, that hold their shape just as well, if you keep them pumped up. Balloon tire makers like Schwalbe know balloon tires cannot really be fast, because they can't be pumped up very hard, so use soft rubber compounds to compensate, then downplay the attendant high wear and lack of resistance to punctures.

In the end, the best argument for balloon tires, is that they provide some especially non-compliant (in other words, hard riding), bikes with the sorely needed road cushioning they otherwise lack. Why do such bikes exist, when we know how to make slender forks and cushioning frames? Well, we can mainly blame the makers, and millions of recent buyers, of bikes made from aluminium. Cheap to make, yet easy to lift, these bikes appeal to buyers whose sole criteria, are price and weight. They test ride them in front of the shop, where they only have a chance to notice the smooth ride from those space hoppers with axles, but not the rolling resistance they will be cursing half an hour into each ride. I'm not here to promote balloon tires as cures for problems of a naive market's creation.
 
The kind of hard riding bike I can support, that could do with balloons lest fillings be shaken loose from our teeth, are those with over-sized tubes, designed to look all Bauhaus Moderne. I think of the Victor Bike (above left) designed to look good, and who cares how it feels. I think of that bulbous fork on my Scrap Deluxe, curved like the steel in a Wassily chair, a chair designed by architect Marcel Breuer to recall the handlebars of his much loved Adler bicycle, and around the references go. Verily that fork is over engineered, to look great. My "Flat Frank" (as I call my 22psi front balloon tire), is what these beautiful forks need. Before letting the air down, I felt like I was holding a jackhammer.

If after all this, you still can't decide,
do as I do, with
Billy Crystal my guide.

Nando, don't be a schnook. It's not how you feel, it's how, you, look.
 
And retro bikes with fat tires look marvewous darling. Ab-so-wutely marvewous. Crave as you might, to die in your sleep, I would rather die of discomfort, with a fashionable corpse left behind me. I would rather work up a sweat commuting on a cool looking bike, than get to work early on a bike with no sense of style. And really, all things considered—headwinds, hills, the art school chicks who will line up to be doubled—by how much will those low pressure tires really make you go slower? If one punctures, take the opportunity to let those girls see how you're not only hip, but Mr. Fix-it as well.

Need convincing that chicks dig fat tires? Then search a few stock photo libraries for romantic pictures of couples with bikes. Not sure if the arty look will lure someone attractive? Just google "art school girl". Not "suicide girl"; us bike bloggers worked hard to win you from porn, we can't have you go back there.

References
1. Sheldon Brown tells me on this page, that "The area of the contact patch equals the weight load, divided by the air pressure. For example, if the air pressure is 50 PSI and the weight load is 100 pounds, the contact patch will be two square inches".

Further Reading
http://yarchive.net/bike/tire_pressure.html
http://www.rouesartisanales.com/article-1503651.html

Comments

Paul Squire
Apr. 30th, 2011 07:20 am (UTC)
Are you sure?
OK 60psi vs 100 does makes a difference. However, a 60psi wide tire will have less drag than a 60psi narrower tire. The contact patch of the wide tire will be more or less circular, the narrow tire's contact patch will be oval i.e.; longer and narrower. Because the wheel is moving forward not sideways, a long contact patch suffers more tire deformation and drag than a short contact patch. Returning to tires with different pressures, further research is required to determine if the circular vs oval benefit offsets the higher pressure benefit. The difference may be less than initially thought.
behoovingmoving
May. 2nd, 2011 12:49 pm (UTC)
Re: Are you sure?
Hi Prof Squire, my case in a nutshell is that a 60psi balloon tire is faster than a 60 psi 23mm tire, but not as fast as a 120psi 23mm tire. And the balloon tire, alas, can never reach such heady heights of high pressure. I hope that makes sense, I am in Amsterdam, so not 100% sure of anything I'm afraid :)

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