A brief history of the Thompson wheel
Spoked closing wheels first came onto the no-till scene in the early ’90s, and were often simply rotary-hoe wheels or row-cleaner ‘spider’ wheels bolted onto the planter closing brackets. This was novel and insightful. While these first-generation spoked closing wheels were certainly improvements over the smooth wheel, they had significant limitations. Rotary-hoe wheels often excessively packed the furrow sidewall (think of a sheepsfoot), and had some issues with accumulating mud and stalks. The row-cleaner wheels (when used for closing) had such long slender spokes that they tended to lift the sidewall too much, flinging chunks of sidewall in all directions, and sometimes roto-tilling out the seed (the extent to which these are problems depend on amount of pressure on the spoked closing wheel, soil conditions, lateral spacing from furrow, and the degree to which the seed is embedded in the bottom of the furrow). Also, the row-cleaner type of closing wheel did no seed firming whatsoever, but luckily Keeton seed firmers (and several small-diameter ‘seed-lock’ wheels) were introduced to the market about that same time.
By the mid-’90s, at least one spoke design was specifically created to provide the closing action demanded by no-till conditions. This design had spokes with a fairly small surface area at the tip, tapering sides of the spoke, and a shorter spoke length. Although an improvement over the earlier attempts, the new design had problems with durability, particularly frequent bearing failure, and with mud accumulation due to the thickness of the spokes at their base. However, the spoke shape was clearly an improvement over earlier attempts at spoked furrow closing from off-the-shelf wheels designed for other purposes.
Enter the Thompson wheel (in 2002), with unique patented features to dramatically improve performance. The thinness of the wheel allows it to easily enter the soil, for excellent breakage of the sidewall. The thinness is also what prevents mud accumulation on the spokes. It simply has nowhere to gather. The blunt tip & tapering sides of the spokes further assist in crumbling the sidewall. The tapering sides gradually increase the resistance the spoke encounters while operating in the soil. This limits the depth, as does the overall length of the spoke itself (considerably shorter than some other designs on the market). So you get just the right amount of sidewall shattering, without digging too deep.