All tires, including those with the E1 designation, have load range and maximum inflation numbers labeled on their sidewalls. The load range identifies how much load a tire can take at specific pressures.
While most passenger vehicles have standard load ranges, light trucks use a system in which letters A to N identify the strength of each tire. Letters farther along the alphabet identify stronger tires that can withstand higher inflation pressures and carry heavier loads. E1 tires have a 10-ply load carrying capacity. This doesn't mean the tire is actually built with 10 plies, but rather that it contains one or two plies of equivalent strength.