OT: Tire pressure monitor

[Jamie]

I was looking on eBay, and seen these monitors, which screws onto the valve stem.

How long have these things been out? And, do you know if they're worth the few bucks?

Thanks!

[Mike Dobony]

Give a link. If they are the ones I tried they are junk. I was over 10 PSI low and not one showed a visual indication of being low.

[Eric in North TX]

One more place for it to leak.

[Joseph Meehan]

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.

[mm]

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.

[claudebetts]

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 happen.

[Sev]

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.

[Goedjn]

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.

[dpb]

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 higher-end vehicles.

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.

[Jamie]

"mm" wrote

Actually, I hope I would feel it. I drive a 22 wheeler for a living, and had my share of flats. It's something for my wife's car.

Here's a link......This is not a "plug" for the seller.

[Jamie]

"Sev" wrote

I have auto regulator on my truck & trailer. Though the equipment isn't mine, I heard it runs almost $2,500 for 22 wheels.

[Jim Yanik]

mm wrote in news: [e-mail]:

If they just screw on,they can get unscrewed by some thief just as easy.

[Robert Haar]

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.

[David Nebenzahl]

Robert Haar spake thus:

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.

[Sev]

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.