AKRON (July 3)—Four tire makers are instituting price increases this summer as high as 5 percent. Cooper Tire & Rubber Co. plans to increase prices on all its passenger and light truck tires by 2 to 4 percent, effective Aug. 1. Continental Tire North America Inc. also raised prices, effective July 1, according to a letter sent to dealers June 18. Prices on Continental and General brands sold to the U.S. replacement market will increase up to 5 percent, the company said. The specific increases depend on the tire line, though it affects passenger and light truck replacement tires. Firestone Agricultural Tire Division is planning a price increase of 3 to 5 percent on all Firestone-brand agricultural, industrial and forestry tires, effective Sept. 1. Michelin North America Inc.´s Uniroyal brand raised prices between 3 and 5 percent July 1. The increases vary depending on tire line, though they apply to passenger and light truck replacement tires.