French tyre manufacturer Michelin posted on Monday a 5.7 percent rise in third quarter sales despite weaker demand in developed markets, and confirmed its full-year forecast for a \"clear increase in operating income.\" Michelin said that sales in the three months from July through September had grown to 5.436 billion euros ($7.1 billion), and had gained 5.9 percent in the first nine months of the year to 16.142 billion euros. The tyre manufacturer said that it had managed to increase the value of its sales despite a 6.7 percent decrease in volumes, in part owing to gains in the value of the dollar against the euro. For 2012 as a whole, Michelin confirmed its previous outlook, for \"a clear increase in operating income before non-recurring items, with a 5.0 percent decrease in full-year sales volume.\" A favourable impact related to raw materials was expected to boost the value of sales by 200-300 million euros, the company said.