Toe In/Toe Out are basic opposites that have inverse effects. When the leading edge of the tires are angled towards each other (no matter how slight it is), the wheels are said to be toed in. If the leading edges of the tires are pointed away from each other, then the wheels are toed out. Too much toe either way isn't good and will cause tire scrub and wear; wear on the outside of the tire if toed in, and wear on the inside if toed out. Why would you purposely set the wheel other than perfectly straight ahead? Well, on most 4x4s you probably won't, but in ideal street conditions, having toe in will make the vehicle track in a straight line, and toeing out slightly will help the vehicle be pulled with the leading tire into a turn during the deflection of the suspension.
Crossover Drag-link Angle With crossover steering, the drag link (at the knuckle) travels in an arc as the suspension cycles. As the drag link becomes parallel to the ground, it reaches its longest parallel distance (to the ground) between the knuckle and whatever the drag link is pivoting off of. This pushes the wheels to the right when the drag link becomes closer to parallel (with the ground), and pulls them to the left when moving away from being parallel (when the suspension droops and drag-link angle becomes greater). Ideally the drag link should be close to parallel with the ground when the truck is stationary. This will guarantee the least amount of distance change in between the vertical plane of the knuckle and the vertical plane of the steering box as the suspension cycles, therefore limiting the amount of knuckle movement and consequently the amount of bumpsteer.
Drag Links and Leaf Springs In a leaf-sprung front end the axle travels up and down and also backwards or forwards as the spring compresses, elongates, and moves towards the pivoting point (the shackle); the axle does not move from side to side (ideally). Since the drag link moves in a side-to-side arc with suspension cycling, it is unlikely one could rid one's vehicle of all bumpsteer with a crossover steering and leaf-spring setup. The best one could do is have the drag link parallel with the ground when the vehicle is at rest. Actually, the "best" one could do would be to put a track bar on the axle that will mimic the arc of the drag link as the suspension cycles. This would almost completely eliminate bumpsteer as explained below in Drag Links and Five-Links. A track bar can also offer a noticeable improvement in handling and stability to 4x4s with very soft front leaves. Sometimes leaf springs don't do a great job of giving lateral support and the front axle has the ability to wander back and forth as forces are put on it (including steering input and road conditions).
Drag Links and Five-Links (Four-Links With a Panhard Rod, Also Pertains to Radius Arm Design) If you have a linked front axle, it is almost certainly a five-link (including the Panhard rod) and not a true four-link. This is for a few reasons, including the sheer difficulty of getting two triangulated upper links not to hit the oil pan. And without having triangulated links, there is a need to laterally locate the axle via a track bar. Luckily this is beneficial with the type of steering that most solid-axle 4x4s run. Much the same as the drag link becomes longest (side to side) when parallel with the ground, the track bar does as well. On that same note, a similar arc is followed with the track bar as the suspension cycles and the track bar pushes the axle slightly from side to side. This can be very good, or very, very bad: if the track bar and drag link follow the same arc, you will have none or almost no bumpsteer, as the track bar's movement of the axle will compensate for the drag link's movement of the knuckle. The easiest way to make this occur is to use a track bar of the same length as the drag link, set at the same angle as the drag link. If you have a track bar that does not follow a similar arc as the drag link, your bumpsteer could be horrendous. The greater the differences in the traveled arcs (of the track bar and drag link), the greater the bumpsteer. Radius-arm design front suspensions use a track bar and two links fixed to the axle. This suspension design will be affected much the same as a five-link would, with the major difference being that an axle can rotate and change caster as suspension cycles, but not on the two fixed radius arms.
Drag Links and Five-Links, but Not Four-Links? To drop off on a tangent for a second, you might have asked yourself why you can't have a four-link with two triangulated links instead of having a four-link with a Panhard rod (truly a five-link, commonly referred to as front four-link) connecting your front axle. Besides the clearance issues of the triangulated links and the oil pan, a triangulated four-link moves the axle straight up and down as the suspension cycles, unlike a five-link (with a track bar) that will move the axle slightly sideways, compensating for the drag link's movement. And since the drag link is still moving the knuckle slightly from side to side with cycling, it will exhibit qualities of bumpsteer. Now, there are always exceptions, and we have seen a front triangulated four-link work well by using a cantilever arm on the axle to feed two tie rods. The cantilever was controlled by a drag link that went from the front to the back of the truck, perpendicular to a normal crossover drag link. This was accomplished by moving the steering box under the floorpan and using a series of pulleys to control it.