I’ve seen such dare a number of times ~ above Michigan roads, and it’s just a bizarre sight. So what’s going on?


To discover out, I referred to as up Woody Rogers from tire Rack, who knows a point or two about alignment, and also I rang increase Ken Lehto, a former Ford chassis technician who worked on a bunch the leaf-spring suspension systems, including the one under the behind of the second-generation Explorer shown in the video. (Full disclosure: Ken is likewise the brothers of onetime gimpppa.org contributor Steve Lehto).


Rogers told me the Dog Tracking happens frequently in straight axle vehicles: The behind gets out of whack, and the systems is frequently just to change the front finish to make the vehicle drive in a straight line. “Often times, it comes after some type of accident,” Rogers told me. “It’s a symptom of probably a lot bigger problem.”


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Lehto agrees, beginning by describing those going on. Essentially, the told me the behind axle is no lined up perpendicular come the axis of the car, and because the behind solid axle always travels essentially perpendicular come its very own axis, it is going to cause some issues.

You are watching: What is dog tracking in cars


“The rear axle is do the efforts to steer the behind of the van to the left,” he created me in an email. “If the driver to be to hold the steering wheel straight, the behind of the truck would want to come approximately from the left and also cause the van to make a right turn - for this reason the driver have to compensate by transforming the wheel come the left.”


What Lehto is describing here is a principle called “Thrust angle,” which tire Rack specifies on the website together “an imaginary line drawn perpendicular to the rear axle’s centerline” the “compares the direction the the behind axle is aimed v the centerline the the vehicle.”

In various other words, those happening through the explorer is the there’s a huge negative thrust angle, which means the rear axle’s heading is markedly various than the chassis’ heading. Here’s a much more thorough summary from Hunter Engineering, a agency that’s been manufacturing car alignment tools for decades:


Thrust angle is something that have the right to be measure on the alignment rack, through tire service company Les Schwab showing an instance of a common alignment paper in the picture below. Notification thrust angle over there on the bottom :


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Keeping the thrust angle as close to zero as possible reduces possibilities of “dog tracking” prefer what’s presented in the optimal video. But, particularly with a hard axle, solving the problem with one alignment isn’t always possible.

That brings united state to the question: How have the right to an axle be pointed that far in the wrong direction in the an initial place? prior to we get into that, let’s have actually a look at the Explorer’s basic suspension setup, i beg your pardon is recognized as a “Hotchkiss” design, employing two longitudinal leaf packs to act as the springs and also to locate the solid behind axle.


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As shown over under a random explorer that I slide under in Kentucky (yes, i risked being shot to take it these pictures), four leafs together consist of a leaf pack, i m sorry is fastened come the underside the a hard axle.


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The end of the leaf spring (which save on computer bushings) are hosted in a frame-mounted shackle top top the rear of the truck and directly ~ above the structure at the front.


The method this all functions is this: as the automobile goes over a bump, the wheel transmits pressures to the axle, which pulls up on the leaf spring, bowing it upward. As the spring flexes, that straightens, and also its fore-aft size gets longer, therefore the rear shackle rotates about its mounting allude on the framework to accommodate.


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With that the end of the way, stop talk about how the axle is situated under the vehicle. We’ll begin with the facility bolt, stood for by the red dotted line above. Also called a facility pin, it goes with a feet drilled through all four leafs. The pin has a ring head top top one end that goes right into a feet in the leaf spring perch ~ above the axle, and a nut on the other end, which sticks through a feet in the sheet spring mounting plate.

The leafs room squeezed with each other and against the perch on the axle via 2 U-shaped bolts accordingly called “U-Bolts,” which wrap roughly the axle, drop under on either next of the sheet pack, and are placed in stress via four nuts on the underside side of a mounting plate.


Looking at the image below (which mirrors my Jeep Cherokee’s rear suspension, i beg your pardon is set up likewise to the Explorers, except inverted), you can see the fore-aft and lateral motion of the axle is eliminated, because the head of the facility pin stays clear of it indigenous shifting family member to the frame-mounted sheet springs.


“In the mounting pad on the axle ,” Lehto told me, “there’s a hole. Once you download the spring, girlfriend make sure that the facility bolt sticks with that hole, and that kinda keeps from shifting fore and aft.”

Lehto described some possible causes of the Explorer’s strange Dog Tracking condition in one email. Because that one, he said, one of the two leaf spring center bolts could have damaged or fallen out of the locating feet in the axle, permitting one side of that axle to transition fore-aft follow me the leaf spring.


If the axle slides front on one side, that will reason both rear tires to toe in one direction, yielding a nonzero thrust angle, and thus make the rear of the car want to drive in a direction other than where the nose of the auto is pointed.


In addition, Lehto claims the front sheet spring structure mount top top the left side can have failed, enabling the spring to move rearward, or the framework mount ~ above the right side could have failed, allowing the entire spring to transition forward.

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He likewise says there might have been a failure in a sheet or in a U-bolt mounting plate. In addition, he told me, a U-bolt can simply have actually loosened, permitting the center pin to come out of its locating feet in the axle-mounted spring perch, and also thus letting the axle transition on one side.

A bent frame could likewise cause together a condition, as might a big disparity in sheet spring stiffness, as a level leaf spring on one end and also a highly-bowed spring on the various other would reason the axle to shift rearward top top the saggy side.


On vehicles with independent behind suspension, the behind toe might possibly be adjusted out, and the dog tracking reduced. Yet this phenomenon is much more common through solid axle vehicles v leaf springs, and also for them, the strange handling linked with this weirdness, also called “crab walking,” usually means fixing a bent or broken bit the hardware.


That said, there’s supposedly a maker called a “thrust alignment plate,” which in reality offsets the leaf spring’s center pin, and allows it come be moved relative to the axle’s feather perch feet to solve thrust angle problems rather simply. It no seem prefer the best method to deal with what’s practically certainly a structure issue, yet it’s exciting nonetheless:


So if you see a automobile that looks come be travel sideways under the road, that probably since the behind axle is spicy in the not correct direction as result of an concern with the frame, the springs, or the method the leaf springs are an installed to the axle. In any kind of case, it way the auto is deeply screwed up, and possibly structurally compromised. Therefore maybe offer them a little bit of space.