The Siam cement Group is to reduce its shareholding in the Michelin Siam Group from 50 per cent to 40 in order to concentrate on its core business. The shares will be purchased by Michelin, the other partner in the joint venture, giving it a 60 per cent stake. Michelin Siam has three factories in Thailand, plus a tyre mould making plant and a steel cord factory. The company makes Michelin brand tyres for vehicles from motorcycles to aircraft.