Muscle Car Suspension Basics - Turning The Corner
If You Want To Maximize Handling, You Have To Understand The Basics Of Suspension Design And Spend Money Where It Counts Most
From the September, 2009 issue of Chevy High Performance
By Stephen Kim
Photography by Courtesy of the manufacturers
You always want to fine tune...
You always want to fine tune with the sway bars and shocks. Also, as soon as you put more load into a car with stiffer springs and sway bars, you need to strengthen the chassis with subframe connectors.
What We Did
Introduce you to suspension basics.
The technology is here to transform any muscle car into a corner carver.
As little as $43 for shocks and more for complete out-of-the-box packages
The import guys-at least the two that are still left-think that coilover technology descended from the chariots that travel the golden streets of heaven, but coilovers are actually very simple devices. Aftermarket tubular control arms are superior to stock arms in almost every respect, but it has nothing to do with the fact that they're built from tubular steel. Such misconceptions aren't so much the product of misinformation as they are the consequence of not having enough information. Likewise, while it's no secret that stiffer springs, bigger sway bars, and adjustable shocks can dramatically improve a car's handling, very few people truly know why. Understanding the principles of suspension design at the most fundamental level is mandatory in order to improve your car's handling, so we'll take a crack at explaining it all.
Some of the information here may seem very rudimentary, but the extreme nature of suspension dynamics requires starting at square one. For instance, a few millimeters in additional sway bar thickness may seem insignificant, but such a miniscule change in diameter can yield a 50 percent increase in bar stiffness. Likewise, if you want to cut your car's body roll angle in half, but don't think sway bars are worth the money, then you'll have to double your current spring rate.
In addition to explaining the fundamentals, loads of hot-button topics need to be addressed. Is stiffer always better? Are linear rate springs junk? Are you man enough for double-adjustable shocks? Do coilovers deserve the hype? Are four-links just for drag racing? Should you replace your knees with urethane bushings? If you want to turn the corner in your understanding of suspension design, then turn your attention to the next page. To get the down-low on suspension tuning, we enlisted the help of Kyle Tucker of Detroit Speed and Engineering, Tom Brown of Heidt's, Bret Voelkel of Air Ride Technologies, and Chris Alston of Chassisworks.
As a result of a larger diameter...
As a result of a larger diameter and a shorter swing arm length, the bottom sway bar is substantially stiffer than the unit on top. In practice, this is because the front sway bar (bottom) must endure greater cornering loads than the rear bar (top). However, differences in sway bar design between a matched set of front and rear sway bars clearly illustrates the effects of diameter and swing arm length on overall stiffness.
Whether you call them sway bars, antiroll bars, or stabilizer bars, they are one in the same. By attaching the left and right sides of a car's suspension together and anchoring them both to the frame, sway bars help resist body roll by increasing roll stiffness. In the front suspension, the sway bar anchors the lower control arms to the frame. In the car's posterior, the sway bar usually attaches from the rearend housing to the frame. As a car's body begins to lean upon corner entry, cornering loads twist the sway bar. Consequently, it is the bar's torsional stiffness that determines how much the body roll is reduced.
The three primary factors that determine a sway bar's torsional stiffness are its diameter and swing arm length and whether it is of solid or hollow construction. In regards to sway bar diameter, stiffness can simply be expressed as diameter. For example, take two sway bars that are identical in every respect except for diameter. A 32mm sway bar (324 = 1,048,576) is approximately 70 percent stiffer than a 28mm one (284 = 614,656).
This exponential relationship means that a small increases in diameter substantially increases stiffness, which is important to keep in mind when shopping for a new sway bar.
Although not quite as extreme as tweaking diameter, changes in swing arm length dramatically impact sway bar stiffness as well. The swing arm is the portion of the sway bar that extends from the frame to the control arm or rearend housing. Lengthening the swing arm reduces sway bar stiffness, while shortening it increases stiffness. For example, shortening the swing arm from 10 to 5 inches results in a sway bar that's twice as stiff.
The splined ends on this Chassisworks...
The splined ends on this Chassisworks rear sway bar allows dialing in preload. This eliminates slop between the bar and the endlinks for improved responsiveness.
The spring rate of a coil...
The spring rate of a coil spring is determined by the wire thickness of the coils, the number of coils, and how tightly the coils are wrapped in a circle (diameter). Linear-rate springs, shown here, have equally spaced coils. On progressive-rate springs, the top coils are closer together than the bottom ones.
As long as your car isn't...
As long as your car isn't a fire-breathing 500hp beast that will see lap after lap on a road course, an aftermarket leaf spring suspension system will suffice. This first-gen Camaro DSE kit feature 175-lb/in tapered springs with an antifriction pad wedged between the leaves, which reduces friction and improves ride quality. A matching set of shocks and heavy-duty shackles are also included.
Although air suspension systems...
Although air suspension systems trace their roots back to show cars, Air Ride Technologies has proven that air suspensions can more than hold their own on a road course. Air is an excellent springing medium; it gets stiffer the more that it's compressed. Likewise, it can also be set up to behave in a very linear fashion. Unlike traditional coilovers, an air suspension can be adjusted at the touch of a button. These trick Shockwave units feature integrated double-adjustable shocks.
Removing the "core" from the middle of a sway bar may suggest a significant decrease in stiffness, but that isn't the case. "Depending on wall thickness, a hollow sway bar can be just as stiff as a solid bar for any given diameter," explains Chris Alston of Chassisworks. "The big benefit is that a hollow bar is roughly 30 percent lighter. Additionally, during the design phase we can easily make changes to the sway bar's overall stiffness by altering the wall thickness of the tubing. Another advantage is that a hollow sway bar tends to 'unwind' faster than a solid bar after it has been twisted."
Bearing the brunt of suspension loads, springs can take the form of coils, leaves, torsion bars, or air bags. A spring's most important job is supporting the weight of the chassis, but it must also allow the tires to follow the contours of the road while providing roll stiffness in the corners. Consequently, optimizing one aspect of spring performance often compromises another, which we'll discuss later in this story.
Perhaps the most important aspect of spring design is its spring rate, which is different from spring load. Spring rate is simply how much force it takes to compress a spring one inch. For instance, a 200-lb/in coil spring requires 200 pounds of force to compress 1 inch. Spring load, on the other hand, is how much weight a spring can support at a given height. While spring rate does not change as a spring compresses, spring load is reduced. In other words, the farther a spring is compressed, the less load it can support. This is why a shorter spring must have a stiffer rate than a taller spring in order to support the same weight.
Shocks damp spring motion...
Shocks damp spring motion by converting kinetic energy into thermal energy. Under rigorous use, a shock will begin to fade and lose its damping ability if it can't dissipate heat quickly enough. To combat this effect, DSE has designed an optional remote-mount reservoir canisters that reduce shock fade by increasing fluid capacity.
Most production cars and race cars utilize linear-rate springs. However, some aftermarket springs have a progressive rate, which means that they get stiffer the more they compress. The logic behind this design is to initially provide a softer rate to help absorb road irregularities, then stiffen up the more it's compressed to limit body roll. The true effectiveness of progressive-rate springs is debatable, but they have amassed legions of followers nonetheless. "When matched with the right shocks, a linear-rate spring can ride and handle better than a variable-rate spring," says Kyle Tucker of DSE. "With a variable rate spring, the shock valving must account for a wide range of spring rates, which can adversely affect ride quality and handling. A progressive spring rate is just another variable to account for when fine-tuning a suspension."
The term shock is the biggest misnomer of any suspension component in existence. Everywhere else in the world, shocks are called spring dampers, which precisely conveys their job description. "Without shocks, springs would just gyrate until the friction from the bushings slowed them down," Chris Alston explains. "Springs simply hold up the weight of the car and absorb suspension loads. By damping the motion of the spring, shocks determine the rate of weight transfer, and optimizing weight transfer is what good handling is all about. The shocks essentially control how the suspension operates, and you can't achieve the ideal valving for your combo without an adjustable shock. I'd venture to say that as long as you have a good set of tires, the shocks are the single most important components of the entire suspension."
Double-adjustable shocks allow independent damping of both compression and rebound. Some single-adjustable shocks change the damping of the compression or rebound, but not both, while others change the compression and rebound valving at the same time in equal amounts. Some adjustability is better than none at all, but double-adjustable shocks allow on-the-fly fine tuning that single-adjustable shocks can't match. "Since you don't have time to swap out sway bars at a road course, the easiest way to dial in a suspension is with the shocks, and you really need the ability to adjust compression and rebound damping independently to do it right," explains Kyle Tucker.
One of the wildcards when...
One of the wildcards when installing a front coilover conversion is the difficulty of mounting them. This Chassisworks setup for fourth-gen F-bodies bolts directly to the stock control arms on the bottom and the factory shock mounts on top by using a supplied adapter. Other vehicles may require bolting or welding new brackets onto the body or frame. Some coilovers can be mounted upside-down, which reduces unsprung weight.
As with the front suspension,...
As with the front suspension, rear coilover conversions can sometimes mount to the stock shock mounts, but certain cars require installing new brackets to the rearend housing or frame. This Chassisworks universal coilover kit includes a crossmember for the upper coilover mounts and ears for the rearend housing, and both must be welded in place. The adjustable lower shock mounts allow tweaking ride height without affecting suspension travel or spring rate.
Unlike a suspension optimized...
Unlike a suspension optimized for a road course or the street, an autocross setup can take the stiff-spring-and-small-bars approach to achieve proper roll stiffness since it operates on a smooth surface. This arrangement would not respond well to elevation changes on a road course and would ride terribly on the street.
In cars originally equipped...
In cars originally equipped with leaf springs, like first- and second-gen Camaros, upgrading to a four-link may or may not be a bolt-in affair. The lower links attach to where the leaf springs used to reside, but the upper links require installing new brackets to the frame. Heidt's four-link kit for first-gen Camaros features a bolt-in upper control arm mount, which is also the rear cradle to which the coilovers attach. While not quite as adjustable as a dedicated drag four-link, the Heidt's design includes a Panhard bar to locate the rearend and offers far more flexibility when subjected to lateral loads to help prevent binding.
In essence, a coilover is simply a shock with a threaded body atop which an adjustable perch and coil spring sit. Changing the height of the spring perch raises or lowers ride height at that corner of the suspension and, when matched with a progressive-rate spring, also alters spring rate. This adjustability allows precision tuning of a car's corner weights. According to Kyle Tucker, however, the primary benefit is the quality of shocks that are typically used in a coilover setup. "Adjustability is a coilover's claim to fame, so most are based on premium double-adjustable shocks," he explains. "Most entry-level shocks are a twin-tube design, which rely on fluid to absorb the motion of the springs. Unfortunately, the fluid can heat up after just a few laps on a road course, which reduces their damping ability. On the other hand, the monotube shock design utilized in most coilover arrangements uses both fluid and pressurized nitrogen for damping. In addition to dramatically reducing shock fade, a monotube offers a finer degree of adjustability."
For street machines that will see little to no time on an autocross or road course, coilovers may not be worth the bucks. On the other hand, if you're building a car that will be driven hard at the track, chances are that double-adjustable shocks and stiffer springs are already part of your game plan. If that's the case, upgrading to coilovers is an easy decision, since they cost just a hair more than a set of premium springs and double-adjustable (non-coilover) shocks.
If optimizing handling is all about controlling weight transfer and body roll, then achieving proper roll stiffness is of paramount importance. Roll stiffness is simply a suspension's resistance to body roll and is determined by the stiffness of the springs and sway bars. Some suspension tuners prefer using stiffer springs and smaller sway bars, while others prefer softer springs and stiffer bars. There is no consensus as to which setup is best. The pros and cons of each method should help steer you in the right direction. A setup with stiff springs and small sway bars allow the left and right sides of a suspension to perform more independently from each other, but compromises ride quality. Soft springs and stiff sway bars preserve ride quality, yet detract from a suspension's side-to-side independence.
Deflection in the bushings...
Deflection in the bushings can harm suspension geometry and limit the rear suspension's ability to put the power down. Although they transmit the most noise and require regular lubrication, Heim joints virtually eliminate deflection, and they also enable the rearend to articulate from side to side to reduce binding.
Interestingly, all the suspension experts we talked to preferred soft springs and big sway bars. "I very much prefer a soft spring and a firmer sway bar," says Bret Voelkel of Air Ride Technologies. "The main job of the springs is to hold the car up, while the sway bars and shocks control the body roll. Throw in some adjustable shocks, and you will then have a wide range of control over ride quality and cornering performance tuning.
"I like using soft springs and stiff sway bars because it rides so much better," he continues. "Let's say you're using a 600-lb/in spring and you want to reduce body roll from 2 degrees to 1. To accomplish this without increasing sway bar stiffness, you'd have to double the spring rate to 1,200 lb/in, which would significantly degrade both ride quality and handling."
The leaf-spring rear suspension system used in many Chevy muscle cars is a primitive yet venerable design. It can be made to work reasonably well, but certainly has its limitations. Not only do leaf springs support the weight of the car, they also act as control arms by managing acceleration, braking, and cornering forces. The result is a compromised suspension design that doesn't do anything particularly well, which is only compounded by the obscene horsepower today's street machines are putting out.
Improved strength is just...
Improved strength is just one of the many benefits of an aftermarket control arm. This piece from DSE features an adjustable cross-shaft, which allow the caster angle to be changed by sliding the entire control arm forward or backward. Adjusting caster angle enables fine-tuning the steering feel and straight-line stability.
Many aftermarket front control...
Many aftermarket front control arms, such as these from Air Ride, position the shock mount lower than stock. That opens up room for a taller shock, which results in greater suspension travel and an improved ride.
Alternatives to deflection-prone...
Alternatives to deflection-prone rubber bushings and noise-prone Heim joints are urethane and Delrin. While urethane bushings are stiffer than rubber, many experts suggest avoiding them because urethane squeaks, requires regular splashes of grease, and still deflects more than many suspension tuners would like. Delrin, a thermoplastic manufactured by DuPont, is becoming more popular due to its strength and low friction.
DSE's innovative Swivel-Link...
DSE's innovative Swivel-Link rear control arm features an outer section that swivels around the inner shaft. Consequently, side-to-side rearend binding is dramatically reduced. The compliance built into the control arms allows the use of softer bushings for reduced road noise.
"Leaf springs will always be around in some form or another because they're simple and inexpensive. If you can get the ride height and spring rate you need out of them, then they'll work just fine in most street cars as long as you're not making a ton of power," explains Tom Brown of Heidt's. "However, the only way to adjust the ride height and roll center with leaf springs is by using spacer blocks. Upgrading to an aftermarket four-link system allows changing the suspension geometry and ride height by adjusting the length of control arms and coilovers. Unlike a drag-oriented four-link, street four-links are designed to allow the rearend to roll and articulate, which gives you excellent forward bite and handling. They're the best of both worlds, and usually lighter than a leaf spring system as well."
Due to the impressive appearance of tubular front control arms, you might assume that their chief benefit over a stock unit is strength. However, as Kyle Tucker points out, that isn't necessarily the case. "It's true that the suspension endures incredible loads, but deflection with stock control arms isn't really an issue in most situations, and most people wouldn't be able to feel it anyways," he explains. "The truth of the matter is that it's much easier to manufacture a control arm out of tubular steel than it is to invest in the equipment necessary to make stamped control arms. While the increased strength of aftermarket control arms may be necessary when matched with sticky tires, their main benefits are improvements in suspension geometry."
Typically, the mounting points of the control arms and ball joints must be moved to achieve any appreciable camber gain. For the most part, these anchoring points can not be changed without seriously hacking up the frame or compromising other aspects of suspension geometry, such as the Ackerman and tie-rod angles.
Although often overlooked,...
Although often overlooked, jounce bumpers are cheap insurance. They prevent the lower control arms from hitting the frame when subjected to severe bumps and act as a progressive-rate spring when compressed.
"Front suspension design is the most sophisticated system on the entire car. Everything is interrelated, and you can't change one thing without affecting something else," Chris Alston explains. "Properly designed control arms can slightly improve the camber curve and move the caster angle, but to really make a difference you have to move the pickup points." Furthermore, the built-in shock mounts offered in most aftermarket control arms eliminate the need to modify a stock arm when converting to coilovers.
For those with well-endowed bank accounts, a new front subframe assembly is the pinnacle of suspension upgrades. Although quality aftermarket components bolted to a stock subframe will get you 90 percent of the way there, an aftermarket clip offers just a wee bit more performance-and looks trick to boot. The limitations of how much factory suspension geometry can be tweaked are no longer relevant with an aftermarket clip, as the mounting points of the control arms, tie rods, spindles, and coilovers can be positioned wherever a suspension designer chooses. "By starting with a clean sheet that doesn't force us to work within the constraints of the factory design, we can move all the suspension mounting points to improve the camber gain and caster while eliminating bump steer," Tom Brown explains. "Additionally, aftermarket clips provide more room for bigger tires, and can be setup with a variety of motor mounts to simplify engine swaps."
For maximum effectiveness,...
For maximum effectiveness, springs and shocks should be mounted as close to the ball joints as possible, and as close to vertical as packaging constraints allow. Failure to do so yields a large linkage ratio, which reduces the effectiveness of the springs and requires a stiffer rate to compensate. One of the few methods of dialing in more camber gain into the front suspension is with a taller spindle, which raises the location of the upper ball joint.
Tremendous gains in handling...
Tremendous gains in handling are possible with aftermarket control arms, coilovers, and sway bars. Aftermarket front clips go one step further with revised linkage pickup points for optimized suspension geometry. Although Heidt's street rod front clips are based on Mustang II hardware, its new muscle car subframe assemblies are a clean-sheet design. They're available for first- and second-gen Camaros and '68-72 Novas.
It's impossible to know what...
It's impossible to know what you suspension's telling you if it's communicating through a sloppy stock steering box. This unit from DSE, which is a direct replacement for the common GM 800 box used from 1964 to 1992, dramatically improves steering feel due to a reduction in internal friction. Furthermore, it is six pounds lighter than stock and features a 12.7:1 steering ratio.