h a l f b a k e r yRecalculations place it at 0.4999.
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While riding along this morning, I noticed that the
bottom
of my tyre deforms due to the effects of my non-zero
weight. Because of the rotation of the wheel, the
deformation moves around the perimeter making the
inner
tube a sort of really-inefficient peristaltic pump <link>
which squidges
compressed air around in a futile loop.
Now. What if we built in compartments to the inner
tube?
Like bulkheads in a submarine, they could isolate
sections
in terms of pressure. In this way, air would not be
pumped
around in a circle. Also, the deformation at the bottom
of
a traditional tyre induces a small pressure increase in
the
whole tube. With compartments, the deformation would
induce a much bigger relative volume change, causing
larger relative pressure increase and proportionally less
deformation. In effect, it would behave like it was
inflated
to a higher pressure.
To construct this tube, you could just have lots of little
sections, each with their own valve. But having 32 valve
holes in your wheel rim is undesirable, as is the tedious
nature of inflating such a system*. So, construct a tube
with bulkheads which are somewhat permeable to air.
This
would allow the compartments to equalize in terms of
pressure with a slow** kinetic, but not fast enough to
move the air around while riding. So, while riding along
it
would behave like the compartments were independent.
If there were 32 compartments, then the deformation in
the lowermost compartment would be 32 fold higher***
relative to a traditional tube. This would lead to a... 5
ish?
fold increase in compartment pressure and related
reduced
deformation. So while riding along you'd avoid
pumping
losses and it would feel like a harder tire. The faster you
go, the more pronounced the effect.
Now, these compartments offer an additional
opportunity.
The bulkhead walls could contain small plastic pressure
equalizing valves. These could be reed-valve based and
be
tuned to produce a musical note. Then, simply specify
your
inner tube in either "the birdy song" or "la cucaracha"****
*although the inherent puncture-resistance may pique
the
interest of cyclists deployed to tactical hot zones.
**as slow as possible to avoid pumping losses and to
frustrate the person tasked with inflating it.
***sort of, I'd expect the bulkheads to bulge a bit.
****no other options.
Peristaltic Pump
http://en.wikipedia...ki/Peristaltic_pump
[bs0u0155, Jul 30 2014]
tireballs - flat proof tire solution
http://www.tireballs.com/pages/shop
[pashute, Jul 30 2014]
[link]
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The whole point of a pneumatic tyre is that the entire tyre acts as the spring. Your solution would give a much harder ride. |
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Harder ride for a given pressure. Just reduce the
pressure a bit. Then you get to use thinner rubber,
smaller valves and pump equipment. |
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Even if the pressure is lower, you have massively shrunk the system that is giving your ‘spring’ from the whole wheel to the single section. |
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That's why a solid rubber tyre doesnt work so well, no matter how squidgy the rubber. |
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Yeah, but imagine the fun of checking your tire pressure in twelve places ! |
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They make "solid" (tough foam rubber) inner-tubes for bicycle tires. Perhaps if the tires of a car were wider (more contact surface area with the ground for weight distribution), such could work for them, too. |
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One of the biggest factors affecting riding effort is rotational mass of the wheels. You're suggesting putting additional valves, layers of inner tube, etc in there, which will increase that mass significantly. In that a hell of a lot of keen cyclers actually use tubeless tyres, I think you're going against trend here. Any gains in tyre work will be well lost by having heavier wheels (both in effort to get up to speed, and also sprung weight for suspension systems). |
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Also, I think you're vastly overestimating the "moving air around the tyre" peristaltic effect. This would only really come into play if the feformation of the tyre bottomed it out against the rim, causing some form of partial seal. I would contend that bike tyres usually deflect less than 30% into the rim, anyone wanting to have minimal drag will set pressure so deflection is much less than that. The actual drag effect comes from sidewall flex, that is flexing the sidewall rubber in and out is felt as rolling resistance, and of course higher tyre pressure reduces this. |
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It would be some entirely novel way to pump dairy products from one place to another. |
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Not to mention the prime churning effect of all those sealed compartments. |
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<slips out to register "Wheel-O-Cheeze" trademark before anyone else can> |
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Done! It's a Feta compli. |
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Ee, damn, you always get the best puns. Still, tons left. |
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