Rubber prices may be due to drop as much as 35% and tire makers may report a 6.8% sales slump in 2009 as the global recession cuts auto demand, according to the government-funded International Rubber Study Group in Singapore. Rubber prices have been on a tear, rising 42% in the last four-months. Prices are 18% higher than alternatives made from oil and may fall as global tire demand plunges the most in three decades, according to Bloomberg.