Monday, May 26, 2008

Pressure Sensing Valve Caps

A few months ago I bought my wife a set of pressure-indicating valve caps from TerraPass. These contain a red LED which flashes when the pressure in the tire is more than 4 pounds below the correct pressure, which is preset the first time you attach them to the valve. I bought them primarily because my wife had suffered two flat tires in a short period. Both times the tire was destroyed and she was convinced she had driven a significant distance with them partially deflated. She says she cannot tell whether they are inflated properly or not, and indeed it is impossible to detect under-inflation visually until it is quite extreme. Modern tires have much firmer sidewalls than the cross-ply tires of old, so the pressure has to get down to about 10 pounds per square inch or less before under-inflation is obvious. This is exacerbated in the case of my wife’s Subaru Legend GT Wagon by its low profile (45 series) tires.

Driving with under-inflated tires is dangerous, and – more important at least in the context of this blog -- even a relatively small loss in pressure increases fuel consumption. Fortunately we have not yet had cause to see the new valve caps in action, though I did test one of them by deliberately deflating the tires. They have the potential to pay for themselves quite quickly in saved gasoline.

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