Talking about riding mowers, not heavy tractors or walk behinds, I use 2 x 6 ramps on 6 x 6 blocks, front or rear. If you run up to where the wheels are over the blocks one can turn /twist the ramps sideways providing full access underneath.
Also one can buy or weld up an axle lever lifter. Placed under the front or rear axle and forcing the vertical handle to the ground, it levers the axle up several inches and locks it there in an over center position.