Goodyear's 'On TheGo' Self Inflating Tire 207
A reader writes with a bit of maintenance saving tech for drivers. From the article: "When was the last time you checked your tire pressure? If you're scratching your head, you might want to put a set of Goodyear's new self-inflating tires on your ride. The company's Air Maintenance Technology was rolled out of the lab this week for debut at a car show in Germany. Commercial truckers will be the first to put the rubber to test, but a consumer version is in the works. A regulator in the tire senses when tire-inflation pressure drops below a pre-set point and opens to allow air flow into the pumping tube. As the tire rolls, deformation flattens the tube, pushing air through the tire to the inlet valve and then into the tire cavity. All this technology, in Goodyear's words, eliminates the need for 'external inflation pressure intervention.'"
Price is key... (Score:5, Interesting)
Contrary to popular misconception (Score:2, Interesting)
Tire pressure should be set by the specific application. In a passenger car that generally has a weight that varies only a small amount over its service life, this tire could save a little time, but since it will almost certainly cost more, I don't much see the point. Car tires don't generally leak that much, and thanks to TPMS, (such as the one in my Chevy Impala with which I can see the pressure in each tire displayed on my dashboard) I can check without having to take the valve stem caps off. When it gets a little low, I top off the tires. However, the pressure that should be in each tire corresponds to the characteristics of the tire, AND THE LOAD ON THE TIRE. If you drive on tires with pressure that is too low, you get degraded performance, a spongier ride, increased likelihood of rim damage due to road irregularities, debris, etc., as well as excessive wear to the left and right edges of the tires. If the pressure is too high, depending on HOW MUCH they're too high by, you run risks ranging from degraded performance, increased chance of a blow-out, and the associated loss of control and crash that often occurs with this sort of thing at high speed, especially dangerous if two or more fail simultaneously. As a minimum, you can expect better fuel economy from your over-inflated tires, but decreased tire life span, as you'll see excessive wear in the center of the tread area, which also means greater odds of a flat from puncture than you'd have running over the same thing with a tire having the proper pressure.
As for load, you must understand that the pressure inside the tire is equivalent to the distribution of weight over the entire area of the contact patch, the area of the tires' tread that touches the surface on which you're driving (the road, usually, though occasionally the sidewalk for more adventurous types). So if your tires are inflated to 50 p.s.i., and they're supposed to be at 25, the area in contact with the road should be about half of what it should be. Some people mistakenly believe their tires should be inflated to the MAXIMUM TIRE PRESSURE marking on the sidewall of the tire, and that's simply NOT TRUE under most circumstances. That's a specification that indicates the greatest internal/external pressure differential the tire can safely and reliably handle, under the normal stresses a tire is exposed to, when used in an application for which it was designed, and still give service life as specified and maybe also warranted by the manufacturer.
So if a tire mounted to a passenger car that weighs 3000 pounds, and has a recommended tire pressure of 30 p.s.i. front and rear, is designed to have a contact patch that is 75 square inches, and you are routinely carrying 1000 pounds (between you, the driver, and all the cargo, and let's say the weight is more or less evenly distributed throughout the car,) the load on each tire is 4/3 what the specified pressure was intended for. You should therefore increase the COLD pressure for each tire, (measured and filled when the car has NOT just been driven, as per the manual of every car and truck I'VE ever owned...) by the same amount, so each tire should be at about 40 p.s.i., which BTW, if you carefully note the shape of the tire when the car is empty, the size of the contact patch, you should find it is the same when the pressure is bumped up to 40, with the extra weight added.
Failure to adjust will result in tires that are overinflated or underinflated, depending on when you failed to adjust. Obviously, if you're carrying 3000 pounds in a car that weighs 3000 pounds, you'll probably void the warranty on car and tires, may damage both, and since the tires are probably not designed to handle TWICE THE RECOMMENDED PRESSURE for that car, you run the risk of catastrophic tire failure.
On SUV's and pickup trucks, esp. heavy duty ones, you'll note that in point of fact, the tires that come on them usually have a substantial overhead, can be aired up to much higher pressure than the recommended. This is because such vehicles