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Baffling thing happened yesterday with my front left Pilot Super Sport tire on my Vagon. I was driving on the freeway in the morning and got a low tire pressure warning. I track my car so I'm pretty aware of the tire pressures and had only a week or two prior set the fronts to 32 after a track day, so I assumed I had picked up a nail or something earlier during that particular drive. The tire pressure monitoring system showed it in the low 20's PSI and I watched it drop in real time over 5 or 10 mins of drving pound by pound down to 13 PSI as I made for a gas station several miles down the freeway. The tire was visibly very low. I filled it to 40 PSI to buy myself room to drive to a tire shop later in the day after I took care of some unrelated business. Once the tire was reinflated, however, there was no further leaking. The tire even added pressure as it warmed. I took it to a tire shop later in the day and they couldn't find anything. No leak. No nail. No gap in the fit against the wheel. Nothing. I set the PSI to 35. Over 24 hours later and there's still no leakage or loss of pressure of any kind.

Very unlikely to be a problem with the tire pressure monitoring system, since tire was visibly low and the PSI readings in the air hose were consistent with TPMS.

So strange. Even if it stays inflated, I doubt I'd ever use the tire at higher speeds or on track. Have any ideas what this could be?
 

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Baffling thing happened yesterday with my front left Pilot Super Sport tire on my Vagon. I was driving on the freeway in the morning and got a low tire pressure warning. I track my car so I'm pretty aware of the tire pressures and had only a week or two prior set the fronts to 32 after a track day, so I assumed I had picked up a nail or something earlier during that particular drive. The tire pressure monitoring system showed it in the low 20's PSI and I watched it drop in real time over 5 or 10 mins of drving pound by pound down to 13 PSI as I made for a gas station several miles down the freeway. The tire was visibly very low. I filled it to 40 PSI to buy myself room to drive to a tire shop later in the day after I took care of some unrelated business. Once the tire was reinflated, however, there was no further leaking. The tire even added pressure as it warmed. I took it to a tire shop later in the day and they couldn't find anything. No leak. No nail. No gap in the fit against the wheel. Nothing. I set the PSI to 35. Over 24 hours later and there's still no leakage or loss of pressure of any kind.

Very unlikely to be a problem with the tire pressure monitoring system, since tire was visibly low and the PSI readings in the air hose were consistent with TPMS.

So strange. Even if it stays inflated, I doubt I'd ever use the tire at higher speeds or on track. Have any ideas what this could be?
When mine did that, turned out to be a cracked rim.

Would hold pressure fine still or on short trips, but at some point while driving, the pressure would drop precipitously.
 

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Did you park in someone else's space? Park too close to someones car door? Annoy you neighbor in some other way???

Here's why I ask. 20 years or so ago my now ex-wife calls and says someone slashed two of her tires. I drive over to where she's at, and sure enough, both right tires are flat. I noticed she was parked kinda jacked up, right side of the car is right on the line in the parking lot, but I didn't think much of it at the time. I jack her car up, pull the wheels, and head for the tire shop. Once there, tire guy checks them and can't find any problems. Then, he looks in the valve stem cap. In each cap, there was a small pebble. Just big enough to push in the valve stem when it's screwed on. The Ex is with me, and tire guy asks her the questions I posted above. "Well, says Ex, I was pretty close to the car next to me, he probably had to get in his car from the passenger side."

Tire guy laughs, and says it's an old trick. Remove the cap, drop in a pebble, and screw it back on. Mystery flat tire, and if you don't dig the pebble out, it just keeps mysteriously going flat...
 

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I did that to a substitute teachers car in school once.

The trick is to just barely tighten the cap down - we tightened it too much, and the tire went flat too quickly and we got caught.

But if you can make it take a couple days to leak down....
 

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Started with '04 BR V, moved on to '09 Slvr V, now '13 CRT coupe
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If the issue arises again, try inflating the tire to your normal pressure, then check around the tire pressure sensor for leakage with soapy water.
There is a small O-ring between the sensor and the retaining nut. Sometimes you can tighten the retaining nut very slightly and that will fix it.
Otherwise, it requires breaking down the tire from the wheel, removing the sensor and replacing the O-ring, if your tire shop has them. A cheaper fix than replacing the sensor.
I've played that game before with a V1 I had.
 

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I'm assuming your valve stem caps are on. If not maybe a small stone got lodged in the stem that let the air out. When you put air in it was dislodged.
 
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