Whether stock or wildly modified,...
Whether stock or wildly modified, well-tuned steering is a must for upgrading any muscle car.
When looking for guaranteed ways to transform the handling and driving characteristics of a muscle car, most rodders go straight for suspension upgrades. While that's not an incorrect plan of attack, the issue is that far too many will stop there and forgo the upgrades to the one system that most completely transforms the feel of a car: the steering.
Fundamentally speaking, steering is the result of transforming rotational input from the steering wheel into lateral motion through the use of a recirculating ball-type steering gearbox (an evolution of the earlier worm and sector design) or a rack-and-pinion. In other words, it's the one input that determines how quickly and how precisely your car reacts. After all, what good is a state-of-the-art suspension if the sloppy steering has the responsiveness of a school bus?
There have been a great deal of advances in technology and better implementation of the fundamental components of steering design since the muscle car glory days. From the factory, steering is typically adjusted for the lowest common driver, so to speak, and that was even more the case in the past when suspension and tire technology were more primitive. Making a car steer like a barge kept people out of trouble. Nowadays, suspension and tire technology, combined with vastly improved steering systems, have advanced vehicle dynamics to the point that today even the cheapest commuter box can typically out-handle the best tuned muscle cars in a stock-versus-stock comparison. Sad, but true. However, don't despair; there are plenty of companies crunching the numbers and working to bring 21st century handling to 20th century hot rods.
There are quite a few advanced steering conversions out there that require entire suspension swaps to perform, but we know few people want to re-invent their front suspension just to update the steering, so we only took a look at kits and upgrades that can bolt into an otherwise stock muscle car with little to no modification. You'd be surprised how difficult that can be to design since so many things need to be considered.
At a glance, steering is a deceptively simple looking system, but the real trick of geometry is getting all of the ratios present in the individual parts of the system to coordinate and create that familiar reassuring feeling of control. So what exactly are these guiding principles that aftermarket manufacturers have to keep in mind when designing upgrades to increase steering performance? Trust us, steering theory gets thick with advanced geometry and physics quickly, and complicated equations abound, but the good news is that you don't have to be a mathematics protégé, engineer, or race car chassis designer to have a strong grasp of some of the basic concepts and how they apply toward making your car perform better.
Rack-and-Pinion Conversions
What models are covered?
'641/2-68 Mustang
What do you get?
Kits include a power rack, mounting brackets, U-joint assembly, power steering hoses, and a complete hardware kit.
What options are available?
Chrome ididit steering columns are the only option available.
Why should I buy it?
Aeroform says their kit installs with basic handtools in approximately three hours and uses existing or readily available power steering pumps and bracket. Plus, at 2.5 turns lock-to-lock, Aeroform claims it's the quickest ratio steering rack on the market and saves significant weight over the original steering system.
Are any modifications required?
Absolutely no cutting, welding, or drilling is required if purchased with the steering column, but stock columns will require minor trimming.
How do I buy it?
Direct from Aeroform, on the website or by phone
How much does it cost?
$895 for the basic kit, $1,495.95 with the chrome column
What models are covered?
'62-67 Nova
What do you get?
The base kit includes a 1? x .125 wall tubular crossmember that replaces the flex-prone stocker, ididit paintable tilt column, plug-and-play wiring harness, floor support bracket, manual rack with billet aluminum rack clamps, Heim joint rear-mounted strut rods (fronts are eliminated), billet steel steering arms, and Borgeson steering joints.
What options are available?
The full conversion package includes the exclusive 1?-inch Church Bar sway bar, as well as tubular lower control arms equipped with chromoly Teflon rod ends (F/K bearings), new eccentric bolts, and Moog ball joints.
Why should I buy it?
The rack installs far forward in the chassis instead of the usual location under the engine, which means that a stock front sump, or any rear sump oil pan, can still be used. The extra room also clears LS swaps and can even accommodate inline-sixes if a 230 or 250 rear sump pan is used. No ground clearance is lost either, thanks to the high mounting location achievable with the custom steering arms. Lock-to-lock steering is reduced from 4 turns to 33/4, which resulted in 2 mph and .66 seconds improvement in the slalom on a station wagon test car.
Are any modifications required?
With the base kit, the forward rubber mounted strut rods are eliminated and replaced with a stronger, rear-mounted system. The passenger strut rod bolts up with a supplied mounting plate that uses existing boltholes from the stock steering, but the driver side requires drilling four ?-inch holes in the lip of the frame.
How do I buy it?
From Church Boys or from one of the authorized dealers listed on the main website
How much does it cost?
$1,600 for the base package, $2,200 for the full package
What models are covered?
'64-65 Comet
'64-67 Fairlane, Ranchero
What do you get?
The rack-and-pinion unit, the mounting brackets, the centerlink, power steering hoses, U-joints to attach the unit to the steering shaft, and assorted hardware
What options are available?
Options aren't really necessary, since the rack is designed to work as either manual or power. To use it as a power rack, plumb it into a pump using the provided hoses. To use it as a manual rack, fill the unit with fluid and put pipe plugs in the hose holes. The rack-and-pinion kit can also be packaged with Dearborn's Mustang II-style front suspension.
Why should I buy it?
Engineered to integrate with stock components with ease, Dearborn says the kit installs in an afternoon with proper tools. Since proper geometry is retained, bumpsteer is not an issue.
Are any modifications required?
This rack-and-pinion system was designed to work with auto trans, column-shift cars, but there is an adapter kit that will work for four-speed manual trans, floor shift configurations. It does not fit column-shifted cars. Depending upon the age and condition of the original power steering pump, an upgrade may be required to provide adequate pressure for low-speed turning.
How do I buy it?
Direct from Dearborn Classics, through the website or by phone
How much does it cost?
Price: $950
What models are covered?
'65-70 Mustang (also manual rack conversion for '79-10)
'55-57 Thunderbird,
'60-64 Galaxie
'55-57 Chevy,
'67-81 Camaro,
'68-72 Chevelle/ El Camino and GM A-body
'62-67 Nova, '63-82 Corvette
Steering Box Upgrade
'63-82 Corvette,
'66-82 A-, B-, C-, and E-body Mopars
What do you get?
Cradles vary from car to car for the rack-and-pinion conversion, and some systems will use center-mount travel bar-style racks, while others use end mounts, but all come with an application-specific cradle, rack-and-pinion, Grade-8 mounting hardware, wiring connectors, universal joints, and shaft support bearing. A new steering column is included when necessary, otherwise the original is retained and modified slightly. Power steering kits add a power steering pump with billet bracket and pulley, and polished aluminum mounting reservoir (hoses are sold separately).
What options are available?
Rack-and-pinion conversion kits are available in either manual or power for most applications, and either a small- or big-block design for first-gen Camaros. 1962-'67 Novas can choose between front or rear steer, while '65-70 Mustangs have options to accommodate Granada spindles and the original-style four-speed linkage. Custom headers specifically designed to clear the rack-and-pinion cradle are available for most GM and Ford kits with small-block engines.
Why should I buy it?
Thanks to a wide array of in-house designed and manufactured steering related parts-including their own columns, steering wheels, rack-and-pinion systems, and steering boxes-Flaming River is one of the few companies that can provide complete branded packages. Also, only new (never rebuilt) parts are used in the kit, allowing stringent quality control. Steering box upgrades are all new as well, and are typically quick-ratio 16:1, except for the Jeep box, which is 20:1.
Are any modifications required?
All of Flaming River's cradle kits, both manual and power, are designed as bolt-ins. No chassis mods, drilling, cutting, or welding is required. Upgraded steering boxes are bolt-in as well.
How do I buy it?
Direct from Flaming River or through the national dealer network searchable on the main website
How much does it cost?
Rack-and-pinion cradle kits start at $1,190; steering boxes start at $259.
What models are covered?
'641/2-70 Mustang,
'67-70 Cougar,
'60-64 Galaxie
What do you get?
The base kit includes the rack, new tie rods, hoses, and specific parts needed to connect the steering column to the rack. The complete kit adds a new aluminum pump and pulley with a billet aluminum bracket.
What options are available?
They can be ordered two ways: with power steering pump or without.
Why should I buy it?
According to Randall's Rack, their crossmember is the strongest design on the market with six Grade-8 bolt mounting points. They also position the rack as far to the left as possible to reduce the angle from the column to the rack. The kit uses correct factory geometry and tie-rod length to prevent bumpsteer, while also providing exceptional header clearance for both small-block and big-block cars with either auto or manuals trans. Also, Randall's kits include the only collapsible connecting shaft on the market to connect the steering column to the rack-and-pinion, which adds a degree of safety to cars equipped with non-collapsible columns.
Are any modifications required?
Zero modifications are needed to mount the rack-and-pinion system to the chassis, since the cradle mounts using six original mounting points that secured the steering box, idler arm, and support tube. Minor modifications are necessary for the early long-shaft steering columns.
How do I buy it?
Direct from Randall's rack, either over the phone on the website
How much does it cost?
$1,695 without a new pump, $1,995 with a new aluminum pump
What models are covered?
'641/2-70 Mustang
'62-69 Fairlane
'60-70 Falcon
'68-71 Torino
'60-71 Ranchero
'69-77 Maverick
'67-70 Cougar
'60-66 Comet
'68-71 Montego
'62-65 Meteor
'60-87 Australian Falcon
'62-87 Australian Fairlane
'71-77 Comet
What do you get?
Kits vary somewhat between models, but all include RRS' rack with mounting brackets, steering column conversion kit with bearings, and an intermediate shaft with U-joints
What options are available?
For those needing a kit that can handle track use, a competition-style power steering pump and braided stainless power hoses with Speedflow fittings are available. Lefthand drive is, of course, an option, since RRS is based Down Under.
Why should I buy it?
Based in Australia, RRS has an extensive model-specific listing of kits for the FoMoCo family. Rather than using the same kit for a similar chassis, RSS prides itself on developing a specific kit for each application on an actual vehicle. For example, the Fairlane chassis has six different part numbers for the three chassis changes Ford made between '62 and '71 (three manual and three power rack part numbers). Plus, all RRS racks have a built-in bumpsteer correction that allows the tie-rod bar to be moved back into correct alignment if the ride height has been altered.
Are any modifications required?
All shorty and mainstream brand tri-Y headers will clear the RRS rack, but some long-tube headers may not fit. Factory four-speed small-block cars will experience steering shaft interference, and will require either a hydraulic or cable conversion. The kit is also not compatible with column shift.
How do I buy it?
Through RRS's American distributor, or direct through the official website
How much does it cost?
Power steering kits start around $2,100.
What models are covered?
'60-65 Comet,
'67-70 Cougar,
'60-65 Falcon,
'64-70 Mustang,
'60-65 Ranchero,
'66-71 Fairlane and Torino (with minimal fabrication)
'64-72 GM A-body available soon
What do you get?
Kit contents vary slightly depending upon vehicle and column type, but all include the rack, a column component kit (steering shaft, firewall mount and gasket, roller bearing shaft support), intermediate shaft, and U-joints.
What options are available?
Power or manual, small-block or big-block, power steering pump kit, upgrade to steel braided power steering hoses, aftermarket tilt column, billet adjuster tie-rod assemblies, and even righthand drive for those of you who drive on the wrong side of the road.
Why should I buy it?
Thanks to parent company, Chris Alston Chassisworks, TCP has a great deal of research and development at their disposal and have used that to create a bolt-in rack that not only functions like factory, but reportedly has the best header clearance of any rack offered for Mustangs. Also, the rack itself is so strong that when installed, it actually becomes a load-bearing member of the chassis and works to stiffen it.
Are any modifications required?
1965-'67 Mustangs will need to trim the factory outer steering column tube to a shorter length; 1960-'65 Falcons need to drill two holes in each framerail in addition to trimming the steering column tube to a shorter length; 1967-'70 Mustangs are 100 percent bolt-on.
How do I buy it?
Direct from TCP's website or over the phone, or through any authorized TCP distributor
How much does it cost?
Pricing starts at $1,398 for a complete manual rack-and-pinion conversion kit; power racks are priced at $2,098, plus power steering pump kit.
What models are covered?
'67-69 Camaro, '67-69 Firebird
'55-57 Chevy, '68-72 Chevelle
'68-74 Nova, '53-82 Corvette
'641/2-70 Mustang
What do you get?
Parts included with the Steeroids kit are rack-and-pinion, adapter brackets, adjustable tie-rod ends, U-joint assembly, power steering hoses, and Grade-8 fasteners.
What options are available?
Kits are standard packages, but you will need to decide whether to purchase the kit to modify the stock column, or replace it with a bolt-in column.
Why should I buy it?
Steeroids kits have a very low turn ratio, typically under three turns lock-to-lock, whereas stock systems can have up to five turns. That means less struggling with the steering wheel when making maneuvers quickly, such as in an autocross, or more importantly when making evasive maneuvers on the street. Since the kit uses an aluminum housing and aluminum tie-rod links to replace the factory steel parts, a Steeroids kit typically reduces weight by 20-25 percent. Also, rather than retaining the factory non-adjustable tie-rod ends, Steeroids kits use adjustable tie rods to help eliminate bumpsteer and allow additional steering tuning.
Are any modifications required?
When purchased with a steering column, no modifications are required whatsoever. Those retaining the factory column will need to modify the end. The kits were designed for V-8 auto trans cars, and may interfere with the stock four-speed linkage; cars with manual cable or hydraulic clutch conversion won't have problems. If you are using different spindles than stock (like Granada spindles), let Steeroids know, and they will supply the correct outer tie-rod ends. Also, columns are standard with GM steering wheel splines; Ford-splined columns are an additional $135.
How do I buy it?
Direct from Speed Direct on the main website or by phone
How much does it cost?
Kits start at $1,500.
What models are covered?
'67-81 Camaro
'70-81 Firebird
'64-72 Chevelle, El Camino, and GM A-body
'62-67 Nova
'55-57 Chevy
'58-64 Impala
'641/2-70 Mustang
'60-65 Falcon
'68-72 B-Body Mopar
'70-74 E-Body Mopar
'28-34 Ford (bolt-in if currently using Vega-style box on a straight axle)
What do you get?
All Unisteer rack-and-pinion Impala kits come complete with all parts needed for installation, including rack, power steering pump kit, steering shaft, and mounting hardware
What options are available?
Packages are engineered per car, so the only optional upgrade is an ididit steering column, power or manual steering, and either chrome or powdercoat finish.
Why should I buy it?
Unisteer kits are designed with simplicity and weight savings in mind. Small, compact, and lightweight, the kit offers maximum ground clearance and can drop up to 65 pounds off the stock front end on some cars. Plus, the rack is designed to match the factory suspension geometry and generate little or no bumpsteer.
Are any modifications required?
No fabrication is required, but some kits do require modification of the original steering column. Also, a new steering shaft is required between the steering column and the rack-and-pinion, and for some cars it must be ordered separately by specifying the year, make, model, engine type, and stock or aftermarket steering column.
How do I buy it?
Direct from Unisteer/Maval or though their large nationwide dealer network
How much does it cost?
Most kits are around $1,500.
What models are covered?
Rack Conversions:
'55-64 Bel Air/Impala/Biscayne,
'62-74 Nova,
'64-72 GM A-body,
'67-81 Chevy Camaro,
'61-78 Mopar A-, B-, E-Bodies,
'65-70 Ford Mustang
Steering Box Upgrades:
'65-70 Bel Air/Impala/Biscayne,
'68-79 Nova,
'64-77 GM A-body,
'67-81 Camaro
What do you get?
Each kit uses POL's custom rack made to their specs, mounting bracket specific to the chassis, tie-rod ends, steering shaft, and U-joints, plus fittings and mounting hardware. Power steering kits also include bolt-on steering arms. Quick-ratio boxes are sold individually.
What Options are Available?
Kits are available in either power or manual, and with the standard black finish or chrome plated. Steering gearboxes are a standard quick-ratio 14:1 package with no options.
Why should I buy it?
More responsive steering and excellent road feel, plus the conversion is specifically designed for each stock frame to be a bolt-on that maintains factory geometry. Kits also have the correct ball center dimension to eliminate bumpsteer on the power rack kit. Quick-ratio boxes are designed to enhance steering feel thanks to precise specifications and tolerances, but without feeling heavy. The 14:1 ratio decreases steering to roughly 3.0-3.25 turns lock to lock.
Are Any Modifications Required?
All kits are direct bolt-on applications, so no chassis modifications are needed. POL will need to know the type of transmission and shifter, as well as small- or big-block and the type of headers or manifolds used. Some quick-ratio box upgrades may require a different pitman arm for proper geometry.
How much does it cost?
Starting at $639.99 for the rack-and-pinion conversion, $249.99 for the quick-ratio steering box
What models are covered?
'55-64 Chevy, '63-72 Chevy II
'63-82 Corvette, '641/2-04 Mustang
'66-77 Bronco, '70-04 Ford truck
'74-08 Chevy truck, '79-08 Dodge truck
'72-06 Jeep, '50s and '60s Fords are in the works
What Do You Get?
Borgeson's power steering conversions seek to make things as factory looking and feeling as possible, so a new rag joint is used on the original column to connect to the modern steering box and a new splined shaft is included, when necessary. Manual steering conversions will get a mounting bracket and power steering pump with hoses; original power steering cars will only need the hoses. Remanufactured boxes are chemically cleaned, inspected, and refinished, and all components are adjusted to exceed factory specifications.
What options are available?
Chrome ididit columns are available for some cars for manual boxes or power steering conversions.
Why should I buy it?
Borgeson says the use of a modern fast-ratio power steering gear as a starting point brings the benefit of variable assist and true, modern power steering feel and response that cars originally equipped with slave-cylinder systems lack. In addition, Borgeson power steering conversion boxes maintain the original ground clearance, simplified steering linkage, and a close-to-stock appearance underhood.
Are any modifications required?
Remanufactured manual boxes are stock parts, so they are all bolt-ins. Some power steering conversion kits require a replacement column shaft, or collapsing the factory column 1 to 2 inches for clearance. Mustangs originally equipped with power steering will require either a drag link adapter, or a manual steering centerlink; early cars will need to have the steering shaft replaced.
How do I buy it?
Direct from Borgeson on the website or by phone
How much does it cost?
Power steering conversion kits start at $898.28
What models are covered?
'67-92 Camaro,
'67-92 Firebird,
'68-74 Nova,
'64-72 GM A-body
What do you get?
A brand-new steering box (not a rebuilt stocker) with completely revised internals using a low-friction gear design.
What options are available?
Bare steel finish or ceramic coating
Why should I buy it?
DSE designed their box to nearly match rack-and-pinion steering performance with a bolt-in 12.7:1 ratio steering gear. This box can be used to replace the common Saginaw 800-series power steering boxes used on most GM cars from '64 to '92.
Are any modifications required?
Despite being a clean-slate design, the DSE 600 steering gear is a direct bolt-on. A new 3/4 x 30-spline rag joint is needed with the box, however.
How do I buy it?
You can buy it direct from Detroit Speed, or one of their authorized dealers.
How much does it cost?
Bare is $495, ceramic coated is $575
What models are covered?
'64-76 AMC,
'67-79 Camaro,
'64-76 Chevelle,
'65-76 Chevy car,
'68-79 Nova
What do you get?
CPP's power steering gearbox is a completely new design with revised geometry inside for a more modern steering feel.
What options are available?
Rubber or stainless braided hoses, new power steering pump (recommended), pitman arm, and rag joint
Why should I buy it?
The firm feeling 14:1 ratio is a moderate ratio that's perfect for everyday driving, while still inspiring confidence for those who want to push things to the limit.
Are any modifications required?
In a few applications it will require a different pitman arm and fitting adapters.
How do I buy it?
Buy direct or through any of CPP's 200 dealers. Call for information on the dealer closest to you.
How much does it cost?
$379.95 for the box without pump
What models are covered?
Just about any car that uses an 800-series Saginaw power steering box from the '60s to the '80s is covered.
What do you get?
In the fast-ratio conversion, boxes receive a brand-new Saginaw worm and piston with 12.7:1 ratio, new bearings, Teflon O-rings, seals, and the shafts are polished to a mirror finish. Also, all boxes carry a lifetime warranty on parts and workmanship.
What options are available?
Ratios are available in 14:1 or 12.7:1, and boxes can get the Extreme Detailing Service, which steps it up from the standard finish.
Why should I buy it?
Each box is tailored to the customer's need, including making sure that the internal stops match the car's steering geometry. If you don't like how the new ratio feels, Power Steering Services will reinstall your old ratio, remove the upgrade charge, and pay shipping both ways. In 15 years, no one has ever taken them up on it.
Are any modifications required?
The box is stock, so no changes are needed.
How do I buy it?
Direct from Power Steering after a brief discussion of your car and your expectations
How much does it cost?
Standard rebuilds start at $225, fast-ratio upgrades start at $325. Add $40 for the Extreme Detailing Service.
Steering Box Upgrades
Not ready to step up to rack-and-pinion, or just want to maintain the originality of your car? There are several good choices out there for a drop-in steering box upgrade. In most cases, an updated quick-ratio box with a modern spool valve can provide as much as 90 percent of the improvement that a rack-and-pinion conversion provides. Plus, installation tends to be a much easier affair, with little or no concern about a loss of turning radius, header clearance, or transmission compatibility.
Ackerman
Early on in the invention of steering systems, most were arranged in a more or less parallel design, meaning that both front wheels turned the same amount in a turn. This works well for low-speed performance, like in the buggies and carts it was originally designed for, but it causes a great deal of problems as speed increases.
Boiled down to it simplest form, the Ackerman concept orients steering angles so that all four wheels rotate around a common point in a turn that correlates with the rear axle. To accomplish that, the front wheel on the inside of a turn rotates more than the outside wheel. Why is that a better design? First, imagine a circle. Now, imagine the outside tire of a car is following the outline of the circle. The inside tire has less distance to cover since it is further inside the circle. In a parallel steering arrangement, the wheels actually end up fighting against one another since the inside wheels want to trace the same line as the outside and end ups scrubbing. In a pure Ackerman arrangement, the inside wheels turn a tighter radius to compensate and create a condition where each tire can cover the correct amount of ground. This arrangement is ideal for most situations, and every car on the road today uses some variation of the Ackerman principle in their steering design.
Things do get quite a bit different in the world of road racing and circle track as pure Ackerman is not necessarily the desired arrangement since many other factors come into play, and energy carried into a turn is far greater. As a matter of fact, some racers use reverse- or anti-Ackermann geometry to compensate for the large difference in slip angle ratio between the inner and outer front tires experienced during high-speed cornering. High-end data acquisitions systems can reveal what adjustments need to be made, but knowing how to correctly read your tires can be every bit as effective.
Caster/Camber
Caster and camber are the two principles most enthusiasts are familiar with since they are two of three components addressed in a standard front-end alignment. To understand caster, it's important to understand the concept of trail, which is most easily demonstrated by a shopping cart's front wheel. The steering axis is located ahead of the wheel, so when the cart is pushed forward the wheel will follow directly behind the steering axis, making it self-straitening and therefore stable and easy to control. If the steering axis were placed vertically above the wheels, there would be zero caster effect and the wheels would tend to wander. The longer the distance between the steering axis and the wheel, the greater the force, or trail, exerted.
On a car, this same force is applied by titling the steering so that the steering axis falls on a point ahead of the wheels' contact patch with the road. Higher caster angles improve straight-line stability, but they also increase steering effort, so most street cars stay at 3 to 5 degrees of positive caster, while racers have been known to experiment with slightly higher angles to promote camber gain through turns.
While caster is a forward or rearward rotation of the wheel from vertical, camber is the amount the wheel is tilted inward (negative) or outward (positive) from vertical. You've likely seen heavy negative camber on the front wheels of race cars, or on an IRS-equipped car with a heavy load in the rear. There are actually two camber angles that are critical to steering and suspension performance: camber relative to the road and camber relative to the chassis. Ideally, the wheel should always operate at a slightly negative camber relative to the road, but this can be challenging since the forces exerted by suspension travel, body roll, and suspension dive must be taken into consideration.
To counteract roll, suspension is designed to travel in an arc toward the chassis, which helps maintain more of the tire's contact patch on the road in a hard turn. Camber adjustments are independent of this and preload the wheel with more or less static camber. This same motion creates camber gain, which is added to the static number and needs to be taken into consideration for serious track cars. From the factory most cars are dialed in to gain slightly positive camber in a hard turn; this creates understeer, which limits cornering ability and helps keep inexperienced drivers safe. Street cars set up for handling often run -.5 to -2.5 degrees of static camber. While that doesn't sound like much, that extra negative camber makes a dramatic difference in a how a vehicle feels through a corner. It also leads to dramatically shorter tread life and can cause the front end to track grooves in the road, so more is not necessarily better.
Of course, that same negative camber setting causes the inside front tire to lose contact patch in a turn, but for open track, autocross, and aggressive street cars, setting the tires for negative camber is the only viable option. As for circle track where surfaces are usually banked and turning two directions isn't a factor, typically the outside tire will be set for negative camber while the inside would get positive camber to compensate.
Understeer/Oversteer
These two aren't settings, but rather the result of all of the steering and suspension chassis choices made. Understeer, also known as plow or push, is the tendency of a vehicle to resist making a turn and "push" toward the outside of the curve. What's actually happening is the slip angle is greater at the front than the rear, due to alignment settings, center of gravity, soft suspension, aerodynamics, or a combination of these and other influences. Since understeer is inherently easier to predict and control, and prevents pushing a car to its traction limit, typically new car manufacturers err toward understeer on factory alignment settings in an effort to keep unskilled drivers safe. In racing circles where chassis are dialed-in for lap times, however, understeer is typically used to refer to the inability to follow the desired line through a corner when a vehicle has hit its traction limit.
Oversteer is the exact opposite; the slip angle is greater at the rear of the car due to any number of the same influences found in understeer, so it tends to get "tail happy," or rotate toward the outside of a turn and will usually result in a spinout without counteractive steering. Cars that exhibit a tendency to oversteer are significantly less stable at any speed, but the effects are exacerbated by driving near the car's limits. Typically, track cars are set up with a slight amount of understeer for stability, but some drivers prefer the quick rotation available with a touch of oversteer-especially drifters.
Wheel Diameter
This is probably the most basic concept that many people overlook when upgrading muscle cars. Most classic cars have steering wheel diameters 15 inches or larger because a larger wheel offers more mechanical advantage, which makes steering easier, especially in cars without power assist. Nevertheless, it also works to decrease the effective steering ratio. Simply by dropping the steering wheel diameter, say from 15 to 13 inches with a custom steering wheel, the steering response will be noticeably quicker. It'll also be noticeably harder to turn at slow speeds, necessitating either power or "Armstrong" steering, but the benefit can be almost as transforming as changing the steering box ratio.
Slip Angle
The nomenclature is a little misleading here since slip angle doesn't pertain to actually slipping or sliding of the vehicle. What it's referring to is the deformation of the tire under load, resulting in a difference of angle between the contact patch of the tire relative to the angle the wheel is steered. You're more familiar with this than you might think; imagine a standard sedan with 15-inch wheels and 70-series tires taking a fast, sharp turn. The tire's carcass and tread rolls and deforms, changing the tire's contact patch causing loss of traction. We actually found a YouTube video (
www.YouTube.com/watch?v=W8UiE7yvO_M.) that offers an excellent example.
As a general rule of thumb, low-profile tires offer much less sidewall deformation, keeping angles low, while high-profile tires can go deep into the double digits. Notwithstanding, beyond the tire's ability to resist deformation, weight transfer in a turn from the inside to the outside tires (as illustrated in the video) is the biggest culprit. The more speed a car is capable of carrying into a turn, the larger the lateral forces acting against the outside tire. More equally loaded tires resulting from a well-sorted suspension will limit weight transfer, and will run at smaller slip angles. Of course, larger disparities will cause the slip angle to increase.
It can actually get much more complicated than that, since slip angle has a direct impact on Ackerman geometry, but as far as steering is concerned, the main consideration is working to create front-to-rear slip angle ratios that are as close to 1:1 as possible. Ratios above 1:1 tend to create understeer, while ratios below 1:1 result in oversteer. Eliminating slip angles is impossible, but controlling them will create more balanced handling and steering response by proxy.
Scrub Radius
Scrub radius is basically the centerline of the wheel relative to the steering axis inclination (SAI). SAI is easiest to explain by breaking the term up. The steering axis is the line between the top pivot point of the spindle (the upper ball joint on cars with upper and lower control arms) and the lower ball joint. The inclination of the steering axis is the angle between the steering axis and the centerline of the wheel. Now to find the scrub radius, we follow the SAI all the way to the ground, and measure the distance between that point and the centerline of the tire patch. If the tire contact patch is outside of the SAI pivot, the scrub radius is positive. If it's inboard, it's negative. Unless you're swapping to a new style suspension system, or willing to do some complicated customizing, scrub radius is set at the factory and not adjustable.
So why do you care? Well, the point where the SAI meets the road is the pivot point on which the tire is turned, so scrub radius has a great deal to do with how the steering feels and how much feedback is generated through the steering wheel. Also, scrub radius is directly affected by wheel offset, so it's a good idea to keep that in mind when pondering new wheels. Small changes won't make much difference, but large ones can affect vehicle handling notably and change the steering dynamics. For example, wider wheels with minimal backspacing create positive scrub radius because the centerline of the tire patch is moved further outside the SAI, which places more stress on steering components and typically increases steering effort at low speeds. On the upshot, it also increases steering feedback and feel, which is vital for control. Conversely, negative scrub radius tends to decrease steering effort and feel.
Generally speaking, older muscle cars tend to have a longer scrub radius, and modern performance cars have a short scrub radius (usually only an inch or so). Sometimes cars having a longer scrub radius experience "tramming" on roads with worn surfaces, such as where heavy vehicles have created ruts. This can create a wandering feel that is sometimes confused with bumpsteer. Wide front tires can also exhibit negative effects of a longer scrub radius as the road camber changes, whereby the road acts alternately on the inside and outside of a tire.
Toe Angle
At its most basic, static toe angle is just the degree the front wheels deviate from parallel to the centerline of the vehicle. On the road, near-zero toe is ideal for tire wear, but due to the flex created by the numerous suspension bushings, compensation is necessary. To get close to parallel at speed, rear-wheel-drive cars always require a slight amount of toe-in, because the forward thrust from the rear wheels causes the compliant rubber bushings in the front suspension to flex rearward slightly. Front-wheel drive is exactly opposite, and requires toe-out, but for the same reasons. Cars upgraded with Heim joints rather than bushings experience far less flex.
There are other considerations as well; toe-in, meaning the centerline of the wheels, will converge at some point ahead of the car. This aids stability at speed and for self correcting, but too much toe-in causes accelerated wear at the outboard edges of the tires. Too much toe-out causes wear at the inboard edges and skittishness over bumps and grooves, but serious track cars often accept that trade-off for the increased steering response available from a light amount of toe-out. That brings up dynamic toe.
Ackerman geometry naturally produces toe-out on the inside wheel in a turn, which helps turn-in, but toe is actually a dynamic setting that varies according to the forces applied on the wheel, and according to camber gain. This concept is actually closely associated with roll steer, which is the result of one wheel rising as the other falls due to weight transfer and cornering force, as in a hard corner. The result is more toe-in on one wheel, and more toe-out on the other, consequently producing a steering effect.
Bumpsteer
Most of you have felt this at some point, especially if you've ever lowered or raised a vehicle, or changed the suspension significantly without compensating for the resultant change in steering geometry. Typically, bumpsteer manifests itself as a tendency for the front end to dart or wander without driver input, especially on a less-than-ideal surface, forcing a concentrated effort to keep the vehicle in a straight line. What's actually happening is the wheel is steering as the suspension moves over the road irregularities because the length between the spindle and the rack or gearbox lengthens, but the tie rod does not. The result is the spindle rotating, or toeing, outward slightly to compensate. Depending on the severity, on the street it can be a minor hassle all the way up to dangerous; on the track excessive bumpsteer is always a liability since it will limit control and traction if a bump or dip is encountered while cornering.
Most modified cars have some small degree of bumpsteer; the real goal is simply to make it small enough that it doesn't interfere. To achieve that, the tie rod has to travel on an arc parallel to the one the spindle follows. That's why bumpsteer often increases noticeably when lowering or raising a vehicle-it changes the angle of the tie rods and consequently the arc on which they travel. The only way to combat it is to try and get everything back in line; in the case of lowered cars, by either raising the rack or steering box (usually not an option), or lowering or raising the outer tie-rod attachment point at the spindle accordingly.
Yaw
This is a term that gets thrown around mostly in racing circles, but having a grasp on what it means will still help with understanding the rest of the concepts. To locate an object in space, we need three things: the X-, Y-, and Z-axis coordinates. When relating to cars, the X-axis is lengthwise, and the Y-axis is side-to-side. However, that doesn't tell us anything about how the object is oriented. Yaw is the concept that describes angular motion and how a car rotates around the Z, or vertical, axis. By definition, a car is always in yaw through a turn, simply because it is headed in a different direction than the nose is pointing-which, of course, means that yaw is related to the slip angle.
Why is that important to know? Because there is only so much yaw that can be exerted on a vehicle before control is lost, and knowing how to make adjustments to keep it in check dictates how much speed can be carried through a corner.
More Sources For Rebuilt And Upgraded Steering Boxes Classic Industries
Huntington Beach, CA; 800-854-1280
www.classicindustries.com
'67-92 Camaro
'67-92 Firebird
'58-96 Impala
'68-72 Nova
Original Parts Group (OPG)
800-243-8355
www.OriginalPartsGroup.com
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'64-77 Chevelle
'64-88 El Camino
'64-77 F-85/Cutlass/4-4-2
'64-73 GTO/Tempest/LeMans
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'59-76 LeSabre
'70-88 Monte Carlo
'59-76 Pontiac Fullsize
'63-76 Riviera
'61-72 Skylark/GS/GSX
'63-70 Wildcat
Year One
Braselton, GA 800-932-7663
www.yearone.com
'67-81 Camaro
'64-72 Chevelle/El Camino
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'53-82 Corvette
'68-72 Impala
'64-72 Skylark/GS
'78-88 Regal/GN