I recently put a spare tire back on my van,that was on it when I bought it in 1990...(its sitting unregistered,so no fears of it failing on the street--I just want 4 non-flat tires to move it around in the yard)..
It is a "Tribune" brand,which I found was one of the cheapest tires available back then,"made in China" is cast right into the rubber..
This tire sat on the rim,fully inflated,lying on the ground for years,then one day I decided to clean up the yard,and I rolled it in my shed..
A good ten years later,I put it on the van,because the left front tire kept losing air due to bead leaks,and I got sick of having to drag out the compressor to pump it up every time I wanted to move the van..(bad enough I had to put a battery in it and rig up a small gas tank to the fuel pump !)..
This tire has never lost a pound of air,has very little tread left,and the rubber shows no signs of dry rot..it appears to have ground up glass mixed in with the rubber,and its a hard compound compared to most tires..when I first got the van in 1990 and drove it with that tire on it,it took a long time to wear the tread down..so I guess not every rubber thing made in China is crap..
I have had several Michelin truck tires,load range E,develop severe cracks in both the tread area and sidewalls in a short time,and though none of them failed,I took them off in fear they would grenade !..my friend who ran a tire shop for 18 years told me the most expensive tires seemed to be the ones most likely to dry rot the fastest..probably because the tread life is 60K miles,they want to be sure you'll need new tires before they wear out....trailer tires start cracking the day you mount them,in my experience too...
I have several old bias plys in my shed that look nice still,including some studded snows "D-78-14" that were made in the late 70's that still look great,no cracking anywhere..too bad they are useless as far as being put on anything that has radial tires,I tried mixing bias plys with radials and found out the hard way it'll make the rear end pass you without any warning when it hits a certain speed on slick roads!..
As far as the law they want to pass forcing you to buy new tires once they are 6 years old,good luck with that...most of my vehicles since I got my licence in 1977,were lucky to have a tire ONLY 6 years old on them...and I had relatively few blowouts and dry rot issues with them..like many things,I guess they "dont make em like they used too"..