New tire will not remain inflated?

Rim split.

Had a similar problem once with one tire that intermittently lost air. It was hard to figure out any pattern as it would be fine for weeks then on occasional mornings, getting ready to get back on the road, it would be low by 40 odd pounds. Instead of 90 PSI, it would read 45 PSI. Took it to shop after shop...they'd remove it, and do a tank dunk, but no bubbles. Ever. Even when they left it totally submersed for an hour.

Then one time, staying just 100 feet from a truck tire shop, I measured the tires early in the morning and sure enough that one tire was low. Took it over to the shop, and he found the leak very quickly after dunking it.

Turned out that the leak was in the wheel, not the tire. Rust through. Those slow leaks would occur because of the cool night would cause the steel wheel to shrink slightly, and air would leak out. Warm up the wheel, and the holes would close back up. Which was why there would be no leak after driving 4-5 miles to get to a tire shop. Those leaks were caused by tiny pinhole rust spots that went all the way through the steel. Since the wheel had been painted white inside, it was easy to spot the rust spots, so I grabbed my roll of Eternabond, cut off little patches, and after cleaning the spots, stuck them on the leaks.

Never had another problem with that wheel. Sold the rig 4 years later but I imagine it's still holding air. That EBond is great stuff.

Who manufactured the tire, where did you buy it, and, how old is it? Is it a 1st quality tire, a second, a retread, a knockoff? I would go back to the place that initially sold/installed it to start. Previous remarks about defective valve stems, possibly defective beads and/or casings or damaged (bent or out of round) rims are valid. Some manufacturers permit the installation of tubes in tubeless tires however you need to make sure you don't have other safety issues first. I've never seen a steel rim with porosity but I have seen cast alloy rims with porosity that leak air.

These issues can be very frustrating however patience is the key.

Chum lee

This is a guess, only a guess

That tire has a weak spot in the side wall
When you park on that spot on the pavement
It leaks air at the bead, after it leaks down enough, it just collapses and breaks bead
As a test Mark that spot with chalk for paint, air the tire and don't park on that spot

If it does not leak after several times of doing this
Park it on that spot, spot down, and see if it goes flat again
You have to make Mark the tire and the wheel before you get it repaired aka aired back up

Once it is aired up and appears to be holding
Do not check the pressure, do not touch the valve
You want to eliminate that from the test,
If it does not go flat when parked on the spot , replace the valve
Heck pay a few bucks and have it replaced now while getting the tire aired back up

Mix dawn with water really strong and spray down the tire and the wheel. Walk away and come back in 5 minutes. You'll see a pile of bubbles somewhere.

many times I have seen your same problem valve stem schraider valve did not seat after you checked tire pressure always put your finger on valve after you check tire your tire will be fine

I think that perhaps the tire itself is defective, but a wheel can also be defective, with a slow leak where the halves are joined together. Both are rare but do happen. Did they do a dunk test on it? Submerge it in water and check. I had a tire pass a dunk test only to discover there was a very tiny cut on the valve stem, manufacturing error. Good luck.

I would have a tire shop put it in a water tank to find the leak.