R4s are the Industrial type tires that are almost as wide as turfs, but with cleats. The cleats are not really very deep and the cleat design is meant to give you the best traction on a wide variety of material surfaces like asphalt, concrete, gravel, or loose soil that are common to construction areas. These tires work very well for loader work and have thicker walls to resist punctures.
The R1s are the traditional agriculture cleat tires that you see on farm tractors. They are designed to be used in loose soil and for draft loads. Their cleats are very deep and are generally narrower than R3 or R4.