Get a big jar of kids bubble soap and find out where it is leaking. Aluminum tires are hard to correct rim leaks once they start. Did you tell them the old one was leaking? They have several options to correct the rim problem so take it back and talk to the place that sold you the tires.
Everything is new. They knew we had a slow leak on the old tire and checked it for a nail or some other puncture. Nothing found. I don't know if they checked the rim. I'm bringing the van in tomorrow to the same garage.
Have them take a really good look at the rim of the rim(where the bead of the tire is). Road salt and moisture tend to corrode the rim after some years right where the tire and rim meet.
The good news is a quick buffing will remove the corrosion for another 5 years. Now that the tire's been mounted on it, the tire itself should be checked for any grunge on the bead it may have picked up.
I had a similar perplexing leak in a wheel, I ended up taking the whole thing to my pond and submerging it. Leak was around the valve stem. With that car, I have to have the guys "permatex" gasket sealer the valve stem to provide a tight seal, otherwise it leaks. Car was from up north with salt. Must have some slight corrosion.
Yes, the valve stem is also prone to corrosion. Should have mentioned that myself, since my last way-too-old tire had to be dismounted a second time to fix the stem leak.
N.B. If you have or intend to have a separate set of winter tires/rims, check the age of the tires once in a while(there's a code on them). When I finally got rid of the Integra(in Summer), its winter rims were shod with 12 year old rubber. That's a very bad thing, and was caused by only running them for about 2k miles a year(winters... doh!)
They were basically worn out two years before I retired(no pun intended!) them. I would not have reinstalled them for another winter, which was a small factor in selling it.