Two metal bars that are put under the rear axle of a
car, so that when the
axle twists during
acceleration, the bars (which point forward) hit the underside of the
car, and stops the
rotation of the rear
axle.
The point of this is to reduce what's referred to as "
wheel hop", which is caused by the
axle twisting by the
momentum created between the axle and the
ground, until the
tires loose grip, and unwinds the
axle (then you're back to square one, twisting the
axle until it the wheels slip).
Also known as "
slapper bars".