Over the last decade, at least one Cup driver has experienced wheel hop problems at Watkins Glen each year, but I do not think TV commentators have ever given a proper explanation of the phenomenon that would satisfy those unfamiliar with it. With the season's final road race approaching, I shall take matters into my own hands. I will explain what wheel hop is, why it happens, and how to correct it.
Wheel hop is a condition where the drive axle of a vehicle literally bounces (or hops) on its vertical axis. It manifests itself during periods of heavy acceleration or heavy braking. During acceleration it can be countered by backing of the throttle; however, countering the phenomenon while braking is harder due to higher starting speeds (obviously higher than zero) and a sudden lack of rear stability.
Our Problem is the product of severe axle wrap (excessive torque turning the axle housing on its roll axis) coupled with an intermittent loss of traction. The axle housing rolls when a rudimentary rear suspension (say a Hotchkiss or two-link trailing arm setup) cannot hold it in place against the torque forces exerted on the axles by the engine and brakes. As the rear tires gain or lose traction (whether spinning the tires or locking the brakes), the axle housing deflects between its natural and stressed positions with enough violence to actually lift the tires from the ground.
The easiest way to correct the problem is to not drive so aggressively, but that would defeat the purpose of a race. The smartest way to correct the problem is to build a multi-link suspension, but that will just make NASCAR's inspectors laugh at you (and possibly call you an "egg-head"). We hear drivers being told to adjust brake bias toward the front brakes to prevent the rear brake lock-up, but this is just treating the symptom.
The problem here is the driveline's stability. Crew chiefs cannot treat this as a simple matter of traction. All the traction in the world will not take the stress off the axles, differential, U-joints, or driveshaft. Changes should start with the trailing arms. Despite the increase in unsprung mass, a sturdier trailing arm would help axle housing resist torque. If there is not time for wholesale suspension changes, shock absorbers can be adjusted to compensate for excessive dive under braking or acceleration. Spring and sway bar changes have little effect in correcting wheel hop.
I have gotten very tired of hearing people say, "Our sport is about people." That is B.S.! Racing is about math and physics taking the human body and technology to its limits. The only time anyone says something is about people, is when they are among the select "people," and that makes them better than everyone else.
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