I recently bought myself a set of 97 Cobra R wheels wrapped in a set of used Michelin Pilots. The tires have about 7mm or so tread left all the way around. I had them balanced, pumped them up to 40 psi, and took off. The next week I noticed my car pulling to the left, and when I checked my tires my front driver tire was low...about 22 psi. I pumped it up and noticed in another week or so (I don't drive the car every day) that it was pulling to the left. Sure enough, same tire, about 22 psi. It happened again yesterday, so I took it to the tire place. They found nothing in the tire and offered to clean the rim and change the valve stem for nothing, so I said thanks a lot and went on my way. What I find even more odd is that it doesn't go flat, it just goes to about 22 psi and stops leaking. What could possibly be the cause of this, and if the rim cleaning/valve stem doesn't fix it, what should I try next?

 

It is the way you describe it, a classic rim leak.The tire can be remounted,after the rim is cleanedand a new valve installed and your problem will be fixed.They may add a bit of sealer around the rim as well ,for good measure.Very common with older aluminum rims.

 

Smple
Fill tire to 40
get 25% dish washing fluid in water
spray it all over the tire, valve, rim
and look for bubbles.

I'm surprised the tire guy did not find.

 

Its not surprising that he didnt find it I get stuck with these problems at the dealership. The rim could be a little bent or just the rim is leaking. As you fill up the tire the tire expands and that might cause a hair line split in between the tire and rim and then when it leaks to about 22psi the gets covered by the tire when it srinks so thats why its not going down more than that psi.

 

BINGO!!

 

Then for $7 get a bottle of Slime. Insert
half of it in the tire and no more problem.