Illuminating test - Light-up tire pressure monitors

Want to maximize your gas mileage, reduce tire wear, and improve safety? Well those are the sort of claims made by the makers of the Air Alert Valve Cap System. The caps they’re selling are the simple screw-on type with valve indicators that blink once the tire’s air pressure falls about 4 pounds per square inch (psi) or more from the initial cold inflation pressure of a tire. We bought a set of four for $24.95 direct from Aviation Upgrade Technologies to try them out for this blog-exclusive look at tire pressure monitoring systems.

Valve cap sensors aren’t new; we tested a mechanical color-coded sensor some years ago under the Accu Pressure name. They worked OK, but we had problems trying to read the color-coded display, which dimmed over time due to moisture fogging. They also required stooping down close to the sensor to read the display. Plus, the sensor was susceptible to road curb damage, and we even had a set stolen on a parked car during our test.

We found that these new, blinking Air Alert stems more accurately sensed pressure changes. Think digital pressure gauge to mechanical stick pressure gauge in comparing it to previous mechanical systems.

The instructions are straightforward and the caps are simple to install, but it’s necessary to follow the instructions precisely to initially calibrate the caps to your car tires’ recommended inflation pressure. 

• Set your tire’s pressure to the recommended inflation pressure and then install the cap. It screws on like a regular valve cap.
• The cap will automatically measure and retain the pressure setting for the life of the cap.
• Should the pressure drop 4 psi or more from the initial pressure, the top of the cap will blink red until the pressure is restored.

We bench-tested each of the four valve caps and found them to accurately flash when the pressure dropped 4 psi +/- 1 psi as claimed by the manufacturer.  In fact, against our pressure calibration gauge, the caps worked within about one half of a psi (+/- 0.5 psi), notably better than claimed. (Aviation Upgrade Chief Executive Officer Torbjorn Lundqvist says that caps are checked at the factory to be within specification of +/- 0.5 psi, despite the advertised claimed tolerance of +/- 1 psi.) We then installed the caps on a Chevrolet Silverado pickup and compared them to the truck’s own tire pressure monitor system, which displays individual tire pressures. Each time the tire pressure fell 4 psi or more, the Air Alert flashed.

Pros:

• The caps are relatively small, just about 1” x ½” in size, so they should be fairly discreet, and they only weigh about 0.35 oz. each.
• We didn’t experience any tire imbalance, but it’s probably a good idea to have the tires rebalanced to compensate for the weight of the valve cap. Mr. Lundqvist says a more miniaturized version of the cap is in the works.
• Accuracy may be satisfactory, but durability is still an open question. They do have a long-life battery -- good for about two years of service or just three weeks if a flashing light condition persists.
• The caps are suitable for a wide range of cars, trucks, trailers with tire pressures from 10 to 110 psi.

Cons:

• Mess-up the initial calibration of the valve cap and you end up with a non-functional system.
• Like all valve cap sensors, you have to walk around the car to observe each tire. We found the blinking light noticeable in most light conditions and it was far easier to detect than some mechanical color-coded pressure loss systems. But we agree with the manufacturer’s advice: the system is not meant as a substitute for monthly tire pressure checks.
• Four psi is a narrow window of air loss particularly with a tire that operates at high air pressure. The natural variance of pressure resulting from the changes in air temperature might routinely trigger the caps to flash. As a comparison, the government-mandated tire pressure monitoring system (which will be mandatory on all new cars starting in 2008 model year) requires activation at margin of 25 percent loss from the vehicle’s recommended air pressure setting. For a vehicle like the Chevrolet Silverado, that would be about 8.8 psi less, resulting in fewer false alarms than the Air Alert System. But, of course, the Air Alert System is providing a more stringent and better early warning system.
• Like all twist-on pressure cap systems, it’s critical to properly hand-tighten the cap. Leave the cap a bit loose and it could actually bleed air out of the tire. And because the caps do stick out a bit more than regular valve caps, they get damaged from curbs.
• Finally, some states restrict use of blinking lights on the wheels; some devices are clearly cosmetic with brilliant illumination. It’s not clear if these add-ons are affected by the same restrictions since the light is not normally on when the tire is properly inflated and the illumination is subdued. But it’s probably a good idea to contact your state department of motor vehicles for advice first.   
• The batteries are not replaceable.

If your car doesn’t have tire-pressure monitors and you’re looking for an economical and simple way of ensuring that your tires are not under-inflated, consider the Air Alert System.

--Gene Petersen

Comments

[John Gear]

Two things I'd like to know are these:

1) Is the nitrogen Costco is putting into the tires superior to plain old air (4/5th N2 already).

2) Why do we settle for "inflate tires cold" when cold can mean anything from -30F in Wisconsin to +90F in the Southwest? Shouldn't each tire come with a Pressure v. Temperature curve so that you could inflate to the proper pressure given what "cold" is in your location? Seems like it's simple physics for the makers to do this, and it could save lots of gas nationwide if we would all fill our tires properly.

[Common Sense]

The use of nitrogen or air should not affect this device as it measures pressure of the gas inside the tire, and does not care what the gas is made of. No, nitrogen is not vastly superior to common air, except in special cases of "dryness", and when working with passenger tires and not space rockets, common air does a great job.

Common air is about 78% nitrogen anyway. Both gasses will expand and contract (for all practical purposes) just about the same. You just cant get 20% better by making the gas 100% nitrogen. Besides, common sense should tell you that common air has done a very good job over the past 100 years.

The superiority of nitrogen over common air is a sales gimic to charge for more services that offer minimal value to purchaser.

Yes, nitrogen is used in NASCAR but, they want to scrape every ounce of advantage they can, and cost is not an issue. For common consumer not driving at 150 MPH or driving 100,000 miles a year (like a big truck fleet), paying for nitrogen filled car tires is an expensive way to look special and not get that much in return for the $ spent. It's a great way to shout to the world that you have too much money.

Besides, when you have a flat on the road, is your lighter powered compressor only going to compress the nitrogen or all the air we breathe?

Save the nitrogen money, and buy your kids an ice cream cone, give your wife something special, or give to charity. You will get far greater value from that action.

[Jake]

Nitrogen has a clear benefit in racing, that of dryness and the resulting known pressure increase with temperature. While dry air and nitrogen both have consistent pressure/temperature curves, tossing in an unknown amount of water vapor means an unpredictable temp/pres curve.

For the street, the additional claimed (note claimed) benefits of nitrogen inflation is reduced corrosion due to water vapor inside the tire. What they don't tell you is nitrogen's smaller atoms may also migrate out of the tire more quickly. In practicality, there is little difference to using compressed air and nitrogen as if you monitor tire pressures on a regular basis, you will soon be 'contaminating' the nitrogen with 'regular old air'.

[Sagaliba]

"Cold" means the ambient temperature for your region for the particular season. In other words, if the recommended tire pressure for your vehicle is 30psi, then you should pump your tires to 30psi at +95F in Southwest summer and the same 30psi at -30F in Wisconsin winter. So there is really no set "Pressure v. Temperature curve." The "curve" that is applicable in Wisconsin would not be applicable in the Southwest. Likewise, the curve that is applicable in winter would not be applicable in summer.

[trucking software]

I have one doubt that will these types live up for longer time or are they simply marketing gimicks

[helomechs]

im an aircraft mechanic and have an excellent understanding of nitrogen i tires. primarily used in aviation because it is inert, pressure changes are far less at altitude, zero moisture so no corrosion inside aircraft wheels etc.

benefits to a car vs. the price people are charging? zero. its a complete waste of money. people would benefit far more from checking their pressure once a week and keeping it proper, which most dont.

cold tire = tire that has been static (not driven) for 3+hours
hot tire = driven 1 mile in last 3 hours.

has nothing to do with ambient temp. although yes ambient temp has something to do with pressure, the "cold max." printed on the tire isnt refering to ambient temp.

[car lights]

a great step in caring for our own safety.

[Woodnowin]

Well, I have purchased 1 set of tires at costco where they put nitrogen in the tires and after 3 years I am looking for a used nitrogen bottle so I can keep some in my garage to put in other cars. Why? Because in 3 years my tire pressure has always checked within 2 psi of the original inflation pressure and I have not had to add any air. Never had that happen in the previous 30 years, and I don't think the michelins are the difference. Don't knock it till you've tried it.

[adam]

I got a pack of these tire pressure valves from walmart, but didn't realize until after I bought them, the "recommended PSI" on my door placard, actually sets the pressure valve as "red" - kinda annoying....my door placard has a recommend of 24psi, a little Kia Rio.

just something to consider. Perhaps I'll air them up to 30 (checking my sidewalls first to make sure those aren't set to 30 PSI on the tires themselves...as I don't want the tires to explode when driving on hot tires in this hot southern weather).

But yea, I was kinda disappointed, cause it won't do me any good, at the recommended pressure, it will always show red (add air...) lol.

Buyer beware :)