SPEED NEWS

SPEED NEWS March 2016

Speed News Magazine - The Official Magazine of the National Auto Sport Association

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T E C H M A T T E R S Spherical bearings and rod ends provide the articulation your suspension needs to function properly without the deflection of a factory rubber bushing. CAUSES, EFFECTS AND CURES S tanding starts are hard on a car, and there are a few NASA classes that begin races that way. A standing start is even harder on a car if it suffers from wheel hop, which occurs when a tire loses and gains traction in rapid succession. Wheel hop also can occur on corner-exit in slower- speed turns where a car is in a low gear and torque multiplication is high. To find out more about what wheel hop is, why it occurs and how to cure the problem, we caught up with Pete Epple, a marketing technician with BMR Suspension, a company that specializes in suspension upgrades for early and late model domestic cars. "Wheel hop can be caused by a variety of things, from the wrong shocks to a better surface than the tire can handle or more power than the tire can handle, but the biggest thing that we really see is bushing deflection within the suspension system," Epple said. "In an IRS car, you would see cradle bushing deflection, differential bushing deflection, and it creates large amounts of movement within the system that causes the tire to lose traction and WHEEL HOP STORY BY BRET T BECKER PHOTOS AND VIDEO COURTESY OF BMR SUSPENSION then gain traction and lose traction and gain traction." Bushing deflection sets in motion an oscillation that occurs throughout the entire rear suspension. The condition is somewhat common on cars with independent rear suspensions, but it can occur on cars with live axles, too, particularly those that use coil springs and control arms. From the factory, bushings are made of rubber, often with voids within the material, which allow for significant deflection. Rubber is great for alleviating noise, vibration and harshness, but falls short of the requirements for track use and racing. The rapid and severe torsional loading and unloading during wheel hop can wreak havoc on a drivetrain. "Through all of our testing and all my previous experience, I've seen wheel hop break everything from the actual differential housing to axles to ring and pinions to even breaking the welds on control arms," Epple said. "It can be extremely violent." Regardless of whether your car has a live axle or independent rear suspension, 18

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