Steering Shafts - Safe SteeringWritten by on June 1, 2003 The Steering Shaft Can Help Protect The Driver
It was an idea brought to light well before the most recent emphasis on safety, and the idea is finally starting to take hold. There will be plenty of drivers who will be thankful for it.
Woodward Machine has been marketing a telescoping steering column for over 12 years. Despite the definite advantages, Woodward still finds the need to explain it to allow every user to get the maximum benefit out of this unique product.
The explanations start in dealing with the misconceptions about the application of collapsible columns in race cars. One myth holds that, in a crash, the steering column is intended to telescope upon being struck by the driver. That simply doesn't happen. An essential requirement of mounting any steering wheel is that the wheel cannot be moveable in or out through any effort applied by the driver. "Shear pins" that would theoretically hold up while driving but yield under the impact of the driver's chest is a myth. The assumption that the driver could somehow benefit from striking the steering wheel with his rib cage instead of his hands is in any case absurd. The whole point of the elaborate driver-restraint systems in use today (harnesses, safety seats, full-face helmets, etc.) is to prevent driver impact with interior objects, especially the steering wheel.
The real function of a telescoping steering column is to accommodate the rearward thrust of a steering shaft resulting from compression of the front end of the chassis. In order for this to happen effectively, there must be no resistance to the collapsing action within the column-that is, no shear pins, tension clips, shim stock, set screws, dirt, or anything else that would inhibit movement of the telescoping parts. On the other hand, there should be maximum external resistance to movement of the end held by the driver, usually in the form of clamp collars installed against shaft support bearings. There is no limit to the number of places the shaft can be stopped or made to resist thrust (the more the better, actually) provided there are no thrust-resisting elements within the telescoping section.
Relying on the angle of a universal joint to force a plain shaft to buckle away from the driver is not an acceptable substitute for an adequate telescoping section. If the wreck is hard enough to break the U-joint apart, you will have a loose shaft waving around. If the U-joint doesn't break apart, it might break off a supporting Heim joint, allowing the shaft to jackknife and pry itself into the driver's lap. If neither breaks, the steering shaft tubing may be guided right up through the support bearings, even around a bend. Debating which of the above conditions is the more dangerous is pointless. A telescoping safety steering column would absorb up to 9 inches of the linear component of the wreck in the first place.
The safest possible steering shaft for very high speeds, of course, is one where both upper and lower segments can telescope. A few Winston Cup teams have used setups like the one described since 1997. The obvious drawbacks of a dual installation for short track use are expense and fabrication time, plus the fact that speeds on a half-mile are not normally high enough to shorten the front of the stock car by 18 inches. On the other hand, one of the safety advantages of an extremely light car is the absorption of collision energy into a "crush zone," which reduces the likelihood of inertial injuries, such as concussion, by allowing the car to shorten itself. Therefore, at extremes of light weight, a tandem system may turn out to be worth the extra work.
Better understanding of safety products and their uses will benefit each racer along the same lines as the increased knowledge of engines and suspension systems have increased any racer's performance. In most cases, it's safety first.