Many people suggest using tyres (tires in the US) as cheap containers in which to grow food. It is a very bad idea as rubber breaks down to a fine toxic dust which cannot be removed from the garden. See this article for more information Here is a brief extract:
“Although tyres remain substantially intact for decades, some of their components can break down and leach. Environmental concern centres on the highly toxic additives used in their manufacture, such as zinc, chromium, lead, copper, cadmium and sulphur.”
Personally, I would never have them in my garden and would never want to grow food anywhere near them and neither do I want to permanently poison my soil!
The other big issue is foam backed carpet used a weed suppressant. Again, find particles of rubber can be left in the soil. Don’t use it.
Updated 25 May 2019