All of them I have seen are only good for spotting very low tyres. By
the time you get there, you should be feeling it. They won't hurt, but
don't rely on them to tell you when you need to check and fill your tyres.
If Jamie is anything like me, he'll never feel it.
But I agree, he has to post a url. His description so far is no good.
I have two different designs already that screw onto the valve stem.
One included a little battery in each one and it squealed when the air
pressure dropped. I don't know why I stopped using them.
Geeze just get a good ol' fashioned air pressure gage and check your
tires about once a week. That way you can give each tire a good looking
over to see for any damage that might have occurred or is starting to
I've been wondering for a long time why some manufacturer doesn't
invent a system to automatically maintain correct pressure. I've even
thought through a couple of primitive designs. The military Hummer has
central tire inflation, but that's got to be too expensive a system for
widespread use, and quick re-inflation is not a normal on road need, a
small, slow pump would do just fine. Most vehicles on the road probably
have tires a bit off optimum pressure- and I've seen some way off.
Could enhance safety and save a lot of gas.
Because if your tire won't hold air well enough so that there's
no real point in that, you should be replacing either
the tire or the wheel, anyway. It's not a big enough
problem to make automating it worthwhile.
You hit the nail on the head -- for passenger vehicles, the per vehicle
cost would make the cost/benefit high enough to make it pretty much a
no-go. Takes a fairly sophisticated system to actually get air
distributed into the mounted tire and don't forget that when you
introduce a new system there's another location for a failure to
counteract the benefit as well.
Note that a significant fraction of the benefit is already available in
pressure-monitoring and warning systems on vehicles from most if not
all manufacturers as either an option or as standard equipment on
If you've got a good idea, where there _might_ be some opportunity
would be in OTR trucking where the mileage is so high and the fuel
usage is also a significant operating cost that makes economic sense to
help minimize that a few percentage points could be a significant total
dollars to a Yellow Freight, say.
Exactly. The mechanism to transfer pressurized air to a rotating tire is
non-trivial and introduces all new failure modes.
In many cases, run-flat tires provide a reasonable (but not cheap)
alternative to automatic inflation systems.
One situation where the inflation systems have an advantage is for vehicles
used in both on- and off-road driving, where you might want to lower tire
pressure for driving in sand, etc.
The factory installed systems that I have seen are quite accurate, often
better than the tire pressure gauges that many people use. Besides alerts on
low pressure, they often provide digital readouts of the pressure in each
tire and can be used to monitor slow changes.
So my curiosity has gotten the better of me: how do those systems (like,
say, the ones on the Hummer) work? How do you get compressed air into a
spinning wheel? Seems like the sealing problem would be pretty horrendous.
Just as McDonald\'s is where you go when you\'re hungry but don\'t really
care about the quality of your food, Wikipedia is where you go when
This is true, and exactly why I envisioned not a central system, but
one which operates independently at each tire. Of course, we are
talking about an environment of vibration and dirt, so it's still a
challenge. I've thought of a mechanical piston type pump, rim mounted,
driven by braking forces, for example, though would still necessitate
electronic controls- I'm sure engineers could come up with better
ideas than mine.
Attn David N: this gives a graphic of how central tire inflation
works, though I've seen much better- just couldn't locate them this
minute. Essentially, air is injected through central spindle, which
connects through a rotating seal.
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