I would like to endorse the comments above regarding the use of tyres to grow Potatoes or in fact use to grow any any food. The rubber compounds in both the carcase and tread contain significant numbers of nasties. Tyres are designed to perform at high speed under quite arduous conditions, absolutely not designed as end of life food growing receptacles! They contain many potential hazards/chemicals, far too many to fully list. I will list just a couple,so that fellow readers who do not have my background can appreciate better what they are dealing with. Firstly the reinforcing Carbon Blacks utilized in the rubber compounds, contain significant amounts of Organo-Nitrogen compounds, blacks of this type are banned for use with any "Potable Water" applications! the reason being these compounds are considered as being high risk carciogens. There are special Blacks made specifically for food contact applications, rubber reinforcing blacks are definitely not suitable. Processing aids, The rubber in the tyres must be made to be strong/resilient/heat resistant; specially designed chemical compounds are encorporated into the rubber compounds to achieve this. The chemical compounds used present problems in many directions, firstly they are not ( dont need to be) pure compounds they contain debris from the chemical synthesis processes used to make them; these same compounds also decompose both during Vulcanization and during the life of the tyre. The Organo-Chemical families many of these compounds belong to include compounds that are considered hazardous and not suitable for food contact. The possibility of side chemical reactions between both the impurities and the debris from the degradation, resulting in compounds that could present significant hazards is real. Are tyres dangerous? yes! when attached to cars driven by idiots and when used as receptacles to grow food; otherwise no!

- Geoff Brooks