Carbon Fiber Driveshaft - Getting Shafted

Carbon fiber is one of the neatest composite materials ever created. Components that are woven from it are incredibly strong, extremely lightweight, and pretty to look at-which helps to explain why carbon fiber is not only used regularly by racers but is also a very popular dress-up for many street cars.

LG Motorsports in Wylie, Texas, now offers carbon fiber driveshafts for C5 Corvettes, which provide much more function than just dcor. The C5 driveshaft-also known by GM as the propeller shaft-spends its entire service life hidden inside the torque tube (in the driveline tunnel where nobody will ever see it). But it works hard and often takes a lot of abuse. Carbon fiber driveshafts have been used in most forms of professional racing for years and with good reason. A carbon fiber shaft will maximize both the performance and longevity of the entire drivetrain.

Carbon fiber driveshafts have a lower rotational mass (weigh less) than aluminum or steel shafts, which allows more of the engine's power to be applied to the ground. Since all C5s came equipped from the factory with lightweight aluminum propeller shafts, however, the couple of pounds saved by carbon fiber is the least of carbon fiber's advantages on a C5.

All driveshafts are inherently subject to a great deal of twisting force as they transfer an engine's torque to the rear tires. "Torsional spring rate" is a measurement of the amount of resistance to this twisting force, and carbon fiber driveshafts have a torsional spring rate a little lower than aluminum and about half that of steel. This means that carbon fiber reduces the amount of driveline shock and the amount of stress on other drivetrain components. This also gives carbon fiber a near-perfect "elastic memory." Whereas the continual twisting applied by engine torque eventually causes metal driveshafts to become permanently twisted like licorice sticks, putting the shaft ends out of phase by several degrees and causing excessive vibration, carbon fiber cannot fail by becoming permanently twisted.

In addition to the twisting force of torque, driveshafts are also subject to bending stress-called "whipping" or "deflecting"-that is caused by very high-speed rotations. As engine rpm increases, the force applied to any driveshaft as it spins faster and faster causes the shaft to bend outward in the center like a jump rope. C5 aluminum propeller shafts have a rubber donut around the center, acting as a bumper, to minimize this whipping. But severe usage can cause the driveshaft to become permanently deformed, creating excessive driveline vibration and stress on other components. The "critical speed" of carbon fiber shafts, the speed at which the driveshaft begins to deflect, is much higher than steel or aluminum shafts of the same size, and the composite nature of carbon fiber gives it very unique vibration dampening characteristics. Its exceptional harmonic dampening coupled with high lateral stiffness and low density allow carbon fiber driveshafts to virtually eliminate vibration problems from shaft whip. This helps improve power output by cutting power losses due to drivetrain vibration, as well as providing a smoother ride-especially at higher engine rpm.