Photo © Rim and Wheel Works, Inc.
A young man came into my shop just the other day with a very odd problem. He was from New York, a refugee from the storm. He was losing air in one of his tires very quickly - about 30 psi in 20 minutes, he said - but only when driving. This problem, besides being screamingly frustrating, was preventing him from getting home. He had been to multiple tire places to try to fix this and had already stumped a large number of tire techs, none of whom could find any leak at all. The gentleman related to me that he had already been called crazy by several techs, and had even had someone tell him he was "doing too many drugs."
No problem. We are the shop of last resort for many issues like this. We get people that have been called crazy all the time. When I had originally talked to this guy on the phone I said, "I can't guarantee that we can find the problem, but I can guarantee that we won't call you crazy." At the time I thought from his description that the wheel might be bent just enough so that the car's weight would cause the tire flex away from the wheel just a little bit as it rotated and so allow a puff of air to escape on each rotation
When he arrived, we gave the wheel and tire a complete leak check, wetting the whole assembly down with soapy water and looking for the bubbles that would indicate air escaping. As advertised, there was nothing. The wheel was not bent at all, blowing my theory straight out of the water. No nails had pierced the tire, nor had any pinholes pierced the wheel, nor was any air coming out from around the valve stem. In fact everything looked just perfect.
"Okay," I said. "What we need to do at this point is isolate the issue." We decided to swap the right and left tires onto the opposite wheels. We figured that if the leaky wheel stayed where it was, we would know that the wheel was the issue. If it started leaking on the opposite side, that would mean the tire was at fault. Luis, my best tire tech started to swap the tires while the customer and I went back to the waiting room to strategize what to do next.
5 minutes later, Luis was back. "Come with me," he said to the customer, "I think I've found the problem." Leading us back to the wheels, he pressed down gently on the valve stem. A furious hissing erupted. "Your tire pressure monitor is loose." Luis said.
Here's the deal. Tire pressure monitors, which are now mandatory on all passenger cars made after 2007, are generally made up of a pressure sensor and a radio transmitter stuck onto the end of a valve stem. The monitor end goes inside the tire, and a small nut threads onto the valve stem to tighten the whole thing down. There's a small rubber gasket on each side of the valve stem hole to ensure an airtight fit. But if the nut doesn't get tightened down completely, the stem can move back and forth in the hole. Pushing down the valve stem pushes the gasket away and allows air to come out rather quickly. Under ordinary conditions, the air pressure pushes the gasket outward, sealing the hole. But when the tire takes the weight of the car, the air pressure goes up substantially. When the car is driven, the air heats up inside the tire, which spikes the pressure even further.
Air under high pressure will do funny things sometimes, and in this case the air eventually reached a pressure where rather than holding the gasket against the valve stem hole, the air began to slip out from under the gasket. At that point the air pressure began pushing the monitor back inward, preventing the gasket from sealing until the pressure had dropped enough for the monitor to slip back into place.
And so, a couple of twists later, the gentleman was on his way home with fully inflated tires. I wish him the best of luck with the aftermath of the storm, and I feel like that may well have been the best thing I've done all week. We can't always volunteer for cleanup duty, or do something to help those who have lost homes, lost power or lost loved ones. But we really are all in this together, and sometimes the littlest things can feel pretty big.
So, to New Yorkers, New Jerseyites and all those affected by this terrible storm - stay safe, stay warm and stay well. To the guy with the trick valve stems - I hope you made it home, dude. But you really should cut back on those drugs...