Funny thing happened to me.
Yesterday, I put my winter tire/rims on my IS. Checked the air pressure - they were from 23 to 30 psi (sitting since spring). I pumped them all up to about 32 psi. I don't have sensors in my winter rims. Then, drove it around for about 5 minutes to be sure everything was OK.
Today, I was driving to an appoinment, and just before I got there I hear rat-atat-tat..........
My destination was a few blocks away, and when I got there my left rear was dead flat.
I finished my business, then put the spare on the car (fortunately it was a nice day) and drove home.
I could not find a foreign object in the tire, so I put the tire in a tub, and pumped it up. I don't see any bubbles ????? It seems to be holding pressure. WTF ???
The only unexpected thing I have found is that, on one of the many, many times I put my pressure gage on my tire tonight to see if it was still holding pressure, one time, when I pulled off the gage, the valve stem did not seal -- was pi***ing air.
I suppose its possible, that, after filling my tire yesterday, the valve stem stuck open, and I did not notice the tire was flat until I drove 10 miles today.
Can anybody come up with a better explanatiion ?

 

Sometimes tires can leak air from the bead but it's usually a really slow leak.

Grab a bottle of soapy water and spray the tire to check for leaks, remember to over-inflate the tire before checking though, 40-50psi.

 

Similar issue with mine is driving me crazy. I have a super slow leak...when it was hot out, once a month i had to put in air. Now that it's cold, every 2-3 days i'm having to put in air. Need to find some other place to repair, took it to get it checked out last week and the shop couldn't find the leak!

 

Did u check inside wear toe side? Maybe the tire got split expose metal...

 

Thanks guys, but its not a slow leak. 20 hours earlier, it was at 32 psi , and it held pressure since the spring.
Soap did not show anything.
The tire is not slit. It looks fine.