What Is Axle Wrap?
Axle wrap is a condition that affects vehicles equipped with leaf-type springs under extreme acceleration and, occasionally, deceleration. When the driver of a leaf spring-equipped vehicle applies excessive throttle, the rear axle housing attempts to rotate around the axles as the tires grip the road's surface. The rotation of the axle housing is defined as axle wrap. Under high-traction conditions, the leaf springs will bend as the axle housing rotates around the axle; this bending or wrapping of the springs lends to the term, axle wrap. In some cases, the rear springs can break, and in severe cases can result in bent rear quarter panels on the vehicle, or the drive shaft pulling out of the transmission or even breaking.
While not a typical problem on street-driven applications, this rotation is a condition that affects race vehicles, particularly drag racing vehicles. When a drag racing vehicle is equipped with an extra-powerful engine and over-sized tires manufactured from a sticky rubber compound, axle wrap occurs as the tires grip the racing surface and full power is applied to the tires. The condition, however, is confined to leaf spring-style suspension systems only. There are a few different ways to combat the problem and ensure that the axle remains in its intended position under extreme accelerated take-offs.
A traction bar is a steel device that mounts beneath the leaf spring and extends forward to the front eye of the leaf spring and prevents wrapping. The traction bar attaches directly under the rear axle housing and is held in place with the same bolts that fasten the housing to the leaf springs. The traction bar is equipped with a rubber snubber on the forward end of the bar, which rests directly beneath the front mounting bolt of the spring. As the throttle is applied and the axle begins to twist against the spring, the rubber snubber contacts the leaf spring and stops the axle from rotating any further.
The chassis can be fine-tuned to give the optimum performance by altering the distance that the axle is allowed to rotate before the snubber contacts the spring. Snubbers in differing heights can be swapped onto the traction bars and the snubbers can also be trimmed with a razor-blade knife to further tune and make fine adjustments controlling the wrap. The axle wrap can also occur when braking heavily. As the tires grip the road, the axle housing can often attempt to rotate around the axle in reverse. This reverse axle wrap is typically due to the forward momentum the axle is experiencing, and special chassis attachments are readily available to cure this rare condition.
@Soulfox -- Oh, things get worse than that with more power, torque and traction. Some vehicles are prone to frame and body twisting due to more torque. That condition is all very related to axle wrap (in other words, take care of action wrap and that twisting will usually be addressed, too).
That is particularly true when it comes to more modern frames with lighter frames and body panels. Still, axle wrap, is something that has been overlooked by home hot rod builders for years and that has led to some horrible consequences.
Want to know what is incredible? How many people spend their time worrying about horsepower, grip and torque but do not think twice about axle wrap. You can cram a huge engine in that car and put some big, sticky tires on the back for more traction, but you could totally destroy your vehicle if you don't do something about axle wrap.
Pro builders know this, but amateur ones should get familiar with it in a hurry.
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