Turns Lock to Lock vs. Overall Steering Ratio
This can be potentially confusing since some prefer to express steering response as an overall steering ratio, which would typically be around 16:1 on a car with traditionally “quick” steering. This ratio is calculated by measuring how many degrees of wheel movement results from one turn of the steering wheel. In the example above on full steering wheel turn (360 degrees) and with an overall steering ratio of 16:1 will yield 22.5 degrees of wheel rotation about the spindle since 360 degrees (in one rotation) divided by 22.5 degrees of measured travel=16, or a 16:1 ratio .
What do we mean when we say turns “lock to lock”? Lock being the hard stop where the steering wheel will not turn when rotated in each direction. We prefer using the lock to lock number because it is a lot easier for you to hop in your car, count the turns of the wheel when rotated all the way from one lock to the opposite lock, than to put your cars front tire on a degree table and measure angular rotation of the tire and wheel about the spindle with one turn of the steering wheel.
An example of how simple this is can be illustrated by using our development car, a 1964 Mustang. The factory stock car without power steering was five+ turns of the steering wheel lock to lock! A handful when trying to maneuver quickly; no fun at all. With our Steeroids power rack and pinion kit installed and no changes to the stock steering arms the driver now makes 2.5 turns lock to lock. This increases the response of the vehicle significantly, yet not to the point of being “twitchy” and subject to over control. No more wild antics just to get the car to turn, just move the wheel a bit and you are turning!
NOTE: It is important know that power steering boost has nothing to do with the overall steering ratio.
This is a subjective area of discussion in talking about handling, but a very important topic. Modern vehicles have significantly better “feel” than those manufactured in the ‘60’s through the ‘80’s. ( It is what we have all become accustom to when we drive a car.) It is not about wear either, it’s about design. If you just look at the number of parts in the linkage between the steering wheel in your hand and the front wheels there is a major difference in opportunity for slop, friction and flex between a modern rack and pinion design and an old steering box design from the “good old days.”
On a steering box design the path to the wheels starts with the box itself which has internal gear lash (play). Next the pitman arm with a joint linking it to a center link (track rod) which as two joints for each inner tire rod. In addition to this the center link has a pivot point called an idler arm for stabilizing the end, and finally the tie rod end. Altogether seven separate connections until you are actually turning the wheel, not including the gear lash in the steering box and the clearance for the re-circulating ball bearings inside the box.
Contrast this to a rack and pinion which has gear lash as well, but no re-circulating ball bearings, and has only two joints for the tie rod ends, and two inner tie rod joints. You can see how even in a new setup there are three more points to add play, and friction, and flexing to the feel. This linkage path is integral to another element that is inherent to both designs; on center feel.
On Center Feel
This is the most noticeable difference between steering box steering and rack & pinion steering. It can be best described by the response you receive while cruising with the wheel “on center”. The vehicle moves when you steer without lag or play. Even a new steering box with new steering parts will have lag. That is because of the extra joints for motion in the system as described in the Steering Feel Section. In addition to this it is very difficult to “back drive” a worm and segment gear found in a steering box. Back drive is when the front tires try to drive the steering wheel back to the center position. The incline of the worm gear ( a spiral shaped gear) introduces a lot of friction that must be overcome by the natural tendency of the steering geometry to self center. The result is a vague and drifty with no center feel and no fun at all.
Rack and pinions have a different design with a horizontal “rack” of gear teeth that are meshed with a pinion gear. This is a much easier physical arrangement to back drive since there is no steep incline to drive against. It is also directly driving the steering with the tie rods with no additional linkage to flex. These facts plus only four steering joints to add friction make the steering try to center itself. This gives the driver a solid, crisp on center feel that is ready to accept steering wheel inputs. The car will then drive as good as it looks with a modern steering system like Steeroids.
Corvette Owners With Factory Power Steering: In addition to these facts your Vette has a power steering servo valve at the end of the pitman arm. This is not like most steering box equipped cars which have the power boost built into the box. On the Corvette the pitman arm has a joint that moves as you turn the wheel. The force of turning the wheel causes a force sensor to activate the hydraulic ram in the direction you steer, and applies power boost to the to the steering. Every control system has “dead band”, an area where no control boost is applied. Some dead band is necessary, but this dead band outside the box when added to the natural poor back drive of a steering box makes the on center position vague with a lot of steering wheel “sawing” to keep the car pointed straight. This only gets worse with age as the joints wear.
All of the previous discussion about feel and on center feel is the basis to understand steering feedback. From the basic design limitations of a steering box it is easy to explain why a car with this system has very imprecise feedback to the driver. All the force necessary for you to feel what the car is doing is absorbed in rotary joints and linkage needed to make the system work. If you add wear on those joints you have a steering system that is ambiguous to drive, it is not “telling” you what you really need to know. This is especially true if you are cornering hard up to the limit of available traction. The last thing you want when the tires are howling is to have no clue what the front end is doing.
Feedback is also affected by the amount of boost your power steering has, if so equipped. This is why a few drivers prefer manual steering over power, but that does not need to be the case. A properly designed power steering system is just as good if not better that a manual system. For one thing fatigue is a factor. That is why most race cars have power assisted steering. Make sure you consider the amount of boost you will get if you are converting. There are ways to limit this with certain pumps. It is well worth the effort to have a car that handles well at speed and that you can easily maneuver to park with the added friction of wide tires, so don’t dismiss the power steering option.
It’s Time to Update!
Classic cars have that iconic look that we all love but they drive like a dump truck! You now know that a steering box has serious technical limitations that can not be corrected by just a steering system rebuild. Even when your car was new the steering box did not provide either the proper steering ratio, feel, on center feel, or feedback that have become the hallmark of a modern steering system. We now take for granted how a modern car should feel. Driving a classic convinces us that something has drastically changed in steering technology since the car was designed, and its time to update.
Rebuilding is time consuming and expensive and the result is the same old technology “refreshed”. Here are some of the benefits of a rack and pinion conversion to consider:
· Truly a modification that is really gratifying; you can easily feel the results.
· Vastly improved handling that technically is not possible with outdated steering boxes.
· Tames the beast – makes the car more drivable and fun to be in.
· Modernization of your classics steering to take advantage of a superior and newer technology.
· Improves your competitive advantage if you road race or auto-cross.
· A rack and pinion conversion is easy to install, and will not eliminate the ability to return the car to factory stock steering if necessary. No drilling, welding, cutting whatsoever.
· Enhances the vehicles resale value.