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A straight axle is a type of axle used on the front suspension of a custom, performance or drag racing vehicle. Consisting of a straight piece of steel tubing with spring pads welded to the axle and mounting provisions for the king pins and spindles on each outer end of the axle, it allows the front of the vehicle to ride higher than a common drop axle. Used primarily in performance applications on rear-wheel drive vehicles, the axle is designed to transfer the vehicle's weight quickly to the rear tires to provide traction and better take-off speed.
The use of a straight axle on the front suspension of nearly any type of vehicle necessitates the removal of the stock front suspension pieces from the vehicle's chassis. Once the frame of the vehicle has been cleared of all chassis components such as A-frames, coil springs and steering gears, the frame is ground clean with a heavy disk grinder. When the position of the axle has been determined on the frame, the perches for the mandatory leaf springs are welded to the frame. With the perches affixed to the frame, the leaf springs can be installed.
The straight axle is commonly mounted under the leaf springs using U-bolts. The front wheel spindles are attached to the axle through the use of king pins, and then the steering components can be installed on the new front suspension. It is critical to the handling characteristics of the vehicle that the axle be mounted correctly by designing in the correct amount of caster and camber for the front spindles. Occasionally, the front axle was installed without brakes to further reduce the weight on the front of the vehicle. Special springs and shock absorbers are commonly used to promote the rapid lift of the front suspension while holding the vehicle in the raised position for a longer time before allowing the suspension to settle back to the typical ride height.
The use of the straight axle as a performance item on racing vehicles reached its heyday in the mid to late 1960s during what was known as the "Gasser Wars" in American drag racing. Advances in front suspension technology replaced the often dangerous and difficult-to-handle straight axle with lightweight, independent suspension pieces. The use and popularity of the "Gasser" type race car has returned in the form of nostalgia drag racing events featuring the straight axle-equipped vintage racers.