Many RVers were using simple 2X4's as blocking material. Additionally, this writer witnessed many blocking examples where only the outside dual was blocked to raise that rear corner. Another no-no, especially for radials. Over time, uneven distribution of weight while blocking can damage the steel cables, the casing and especially the sidewall. In some cases, the damage may not be readily visible until after a failure has taken place.
Maximum support is mandated in order to avoid warranty discrepancies and premature tire failure.
Here a few simple examples provided by the Michelin Technical Group that further exemplifies the correct and incorrect methods. F igures one and two show the correct method of using wood blocks to support the footprint of a single tire and the rear duals of a typical motorhome. Notice how the boards extend well beyond the actual tire footprints. If additional height is needed for proper leveling of the refrigerator, a progressive set of boards may be used as long as the bottom board is the longest and the widest and the additional boards are progressively shorter. The uppermost board that is in direct contact with the tire still must maintain the full tire footprint, and then some.