Winged tips (points) cost more than conventional tips (figure 3a). Typical winged tips are 6 to 16 inches wide with 1 to 4 inches of lift, and a 40- to 60-degree sweep angle. Winged tips should be designed to fracture the soil uniformly without lifting or furrowing the surface excessively. If the surface is not being lifted slightly, the ground may be too wet or the winged tips may not have enough lift.

About 25 to 55 percent more horsepower is needed to pull shanks with winged tips, but often the shanks can be farther apart. Winged tips set behind the leading edge of the shank improve efficiency and reduce the amount of horsepower needed to pull the subsoiler. If you consider the volume of soil loosened per horsepower, shanks with winged tips may be more efficient than shanks with conventional tips (figure 3b).

Subsoiler and shank tip equipment manufacturers have invested lots of money and time developing the most efficient subsoiler tips. They should be able to help define the best tip available for specific conditions in the field.

Figure 3a—Winged tips on subsoiler shanks (left) come in various shapes and designs.
Conventional tips (right) are wedge shaped and are easy to replace.

Figure 3b—Winged tips on subsoiler shanks (left) require more horsepower to pull through the
ground, but typically fracture more of the soil than conventional tips (right).

Parabolic shanks (figure 4a) require the least amount of horsepower to pull. In some forest applications, parabolic shanks may lift too many stumps and rocks, disturb surface materials, or expose excess subsoil. Swept shanks tend to push materials into the soil and sever them. They may help keep the subsoiler from plugging up, especially in brush, stumps, and slash. Straight or "L" shaped shanks have characteristics that fall somewhere between those of the parabolic and swept shanks.

Figure 4a—Shank designs include: swept, straight or "L" shaped, semiparabolic,
and parabolic. Shank design affects subsoiler performance, shank strength,
surface and residue disturbance, effectiveness in fracturing soil, and the
horsepower required to pull the subsoiler.

Shanks should be designed to handle rocks, large roots, and highly compacted soils.

Shanks usually are from ¾ to 1½ inches thick. Thinner shanks are suited for agricultural use. Thicker shanks hold up better in rocky conditions, but require larger, more powerful equipment to pull them and disturb the surface more. Bent offset shanks, such as those found on Paratill subsoilers, have a sideways bend (figure 4b). Some testing has shown that bent offset shanks disturb surface residue less than straight shanks.

The typical spacing is 30 to 42 inches between shanks. Shanks should be able to reach 1 to 2 inches below the deepest compacted layer.

Figure 4b—Bent offset shank.

Shank spacing and height should be adjustable in the field. Towed subsoilers should have gauge wheels to control the shank's depth. Conventional ripper shanks, typically found on dozer equipment, work reasonably well when winged tips are added and may be suitable for many jobs and locations.

Shanks With Shear Bolts

Shanks with shear bolts (figure 5a) are better suited for open ground with few rocks. If the shank strikes a rock or buried log, the shear bolt breaks, allowing the shank to swing back. The subsoiler must be lifted out of the ground, the shank swung back into place, and the shear bolt replaced. Shanks with shear bolts typically are cheaper than shanks that reset automatically, but will cost the operator time in the field replacing shear bolts.

Figure 5a—Shanks need to be mounted to subsoilers so that the shank can
survive if it runs into rocks or stumps. The shank above is protected by a
shear bolt designed to break if too much force is put on the shank.

Shanks That Reset Automatically

Shanks that reset automatically (figure 5b) use a springloaded mechanism that allows the shank to hinge back when it hits objects in the ground. The shanks typically withstand 3,000 to 7,000 pounds of force before hinging. The shanks snap forward and reset after the subsoiler has passed the object.

Shanks that reset automatically are more expensive than those that rely on shear bolts, but require less repair time in the field. Some subsoilers use hydraulic systems with accumulators (hydraulic devices that store energy) to absorb force on the shank.

Figure 5b— This photo shows shanks with springs that allow them
to pull back when they strike an object, resetting themselves
once they have cleared the object.

Coulters (figure 6) are sharpened round metal disks that roll in front of the shank. They cut slash and surface residues so the materials don't jam on the front of the shank and plug the subsoiler. Coulters for forest applications must be able to withstand forest conditions and impacts with rocks and stumps. Their height should be adjustable and they should be larger than the standard 20- to 24-inch diameter coulters, so the mounting frames clear residues on the forest floor and will not plug up the subsoiler. Coulters come in several designs, including straight and fluted.

Figure 6—Coulters help cut slash and other surface residues
so they don't hang up in front of the shanks. The coulters
can be straight (top) or fluted (bottom).

Toolbars (figure 7) are configured in a straight line or in a V. Some subsoilers have a double straight toolbar to stagger shanks, allowing better clearance. V-shape designs are said to require less horsepower to pull. Frames should have at least 32 inches of clearance under them when the shanks are sitting on the ground surface. This is especially important in forested or brushy areas.

Figure 7—Shanks can be attached to the subsoiler frame or toolbars in a straight
line (top) or in a V-shape (bottom).