typically consists of natural rubber with a very high sulfur level (up to 8 phr), to get a relatively stiff rubber, with sulfur promoting the adhesion with the steel cord. The basis of the tire is formed by the carcass, normally a mixture of NR (natural rubber), SBR and BR. It should have a very good adhesion to the polyester cord, used as reinforcement. And the inner side of the tire is formed by the inner liner, normally consisting of halogenated butyl rubber (IIR) For all these compounds with their different properties different accelerators and mixtures of accelerators have to be used to obtain the required properties. A vulcanization accelerator is typically used in combination with sulfur as the cross-linker, and with zinc oxide and stearic acid as activators. Other additives can be added too, but for the cross-linking reaction, those mentioned above are the most important. The various types of rubber used in the various tire compounds all have different vulcanization characteristics, like speed of cure (cure is the crosslinking reaction) and extent of cure (the number of cross-links). A typical passenger car tire is vulcanized for 10 minutes at 170 °C. Many accelerators and various mixtures thereof are typically used to ensure the vulcanization of all the component compounds have completed during the 10 minute process. Classification There are two major classes of vulcanization accelerators, primary accelerators and secondary accelerators or ultra accelerators. Primary Of the primary accelerators the major group used in tire manufacture is formed by sulfenamides. These are produced by an oxidative coupling reaction of mercapto-benzthiazole (otherwise called mercaptobenzothiazole) (MBT) with a primary amine like cyclohexylamine or tert-Butylamine. Secondary amines like dicyclohexylamine can be used also but result in much slower accelerators. Such a slow accelerator is required in the steel cord adhesion compound mentioned above, because for optimal adhesion a slow cure is required. Another important group of primary accelerators is formed by the thiazoles. The two main products are mercaptobenzothiazole (MBT) and mercaptobenzothiazole disulfide (MBTS), a product formed by oxidative coupling of two MBT molecules. The thiazoles are used for the vulcanization of thick articles, and as basic accelerator in EPDM compounds (ethylene-propylene-diene rubbers), in combination with mixtures of ultra-accelerators. In the vulcanization of neoprene or polychloroprene rubber (CR rubber) the choice of accelerator is governed by different rules to other diene rubbers. Most conventionally used accelerators are problematic when CR rubbers are