Muscle cars have come a long way since the 1960s when performance was defined strictly by how quickly the car accelerated in a straight line. Today, the definition is far more encompassing, including all aspects of driving, including ride, handling, and braking.
But taking one of those cars of the ’60s or ’70s and making it more capable in the corners, while also improving its braking performance and its ride quality can compromise some collector car norms. We thought the best way to address this challenge would be to break it down into systems.
The process outlined here is certainly not chiseled in stone. We’ll present the various facets of this approach and let you decide on the actual sequence. So, for example, if better shocks are right up at the top of your “must-have” parts list, that’s certainly acceptable. You’ll have to determine the most effective place to begin on your car based on its current state.
Muscle Car Suspension Basics
As with most systems, the best process is more successful when building on a solid foundation, so that’s where we’ll start. Before we can begin with modifications, the car’s basic suspension must be in solid shape. For the sake of this story, we’ll assume you’ve just acquired the muscle car of your dreams and that its suspension is in proper order. To verify this, the areas that will require close inspection include ball joints, upper and lower control arms bushings (front and rear), body bushings, and steering components like tie-rod ends and even the steering box itself.
Performance Tires & Wheels
The 600-pound gorilla in the room throughout this discussion is the topic of tires and wheels. One way to drastically improve handling is to replace that spindly set of 215/60R15 radials mounted on 6-inch Rally wheels with a set of 315/40ZR18-inch soft-compound tires on the rear and 275/40ZR18 on the front mounted on a set of lightweight, aluminum race wheels. Even a bone-stock ’69 Chevelle can be made to feel more like a go-kart with just the addition of fat wheels and tires.
But giant steamroller tires won’t cure a weak suspension. So, while a contemporary set of large-diameter lightweight wheels and sticky tires would no doubt improve handling, performance, and traction when added at any point along our theoretical application of suspension upgrade ideas, without the proper suspension to back them up, fat tires and wheels will only take you part of the way.
Muscle Car Suspension Upgrade Basics
With a solid base for a suspension, you can begin the approach to improving handling. This will require a working knowledge of how suspensions operate, which involves understanding the definition of certain terms. When discussing handling characteristics, you will quickly run into terms like understeer and oversteer.
Understeer describes a car that tends to “push” or “plow” as it enters a corner, with the steering wheels losing traction so that the car continues straight even with more steering input. The opposite of this is oversteer, where, as the car enters the corner, the back end loses traction and comes around. The NASCAR boys call this “loose” as opposed to “tight” for understeer. A car that is neutral or one that is stable entering a corner is what is generally considered to be the goal, although that comes down to driver preference. These two opposite situations can also occur almost simultaneously when entering a corner, where the car understeers on corner entry and then quickly snaps into oversteer on corner exit. All of these wild gyrations can be controlled with the right modifications.
Most ’60s and ’70s cars arrived on the showroom floor with suspension designed to understeer, since this is generally considered a safer situation for average drivers, compared to oversteer. Because of this, we will approach the improvements in this story based on a vehicle suffering from inherent understeer, as it would have in factory form.
Adding or Upgrading Anti-Sway Bars
Once the front and rear suspension systems are deemed to be in good shape, a quick and easy way to address understeer is with a larger front anti-sway bar, often more simply referred to as a sway bar. Most of our recommendations will use GM cars as examples, but these same ideas will also apply to Fords, Mopars, or any other traditional rear-drive cars from this era. A typical front sway bar diameter might be ¾-inch in diameter. Adding a larger and stiffer diameter front bar of 1- to 1 1/8-inch diameter will reduce body roll on corner entry and will offer an instant improvement in overall handling.
Sometimes, on a car with near-stock front suspension, the addition of a bigger sway bar will create the need for a rear sway bar to reduce understeer by reducing rear body roll. But then, at some point, most GM coil-spring cars will also need softer rear suspensions to allow the front to work properly. We have spent many years working with Doug Norrdin at Global West Suspension, improving the overall handling on our ’65 Chevelle and making the front stiffer and rear softer eventually allowed the car to work properly. This may not be the case with leaf-spring or torsion bar vehicles.
Springs/Ride Height
Many cars of this era also employed a rather tall production ride height. Handling can be improved by simply lowering the car. The best way to lower the ride height while improving handling would be to replace the front springs with shorter, higher-rate versions. A typical spring rate for ’60s and ’70s cars would be in the range of 350 pound-inch rate. This means the spring would compress one inch when 350 pounds is applied to the top of the spring.
To improve handling, increasing the rate to anywhere from 550 to 750 pound-inches will offer several advantages. First, this spring will be much shorter in free length, which often offers the freedom to install the spring without the need of a coil-spring compressor. This higher-rate spring will limit front body roll. This is advantageous because most ‘60s and ’70s front suspensions were designed to induce understeer by using a camber curve that rolls toward positive camber when the suspension is compressed, which is not an ideal situation.
For example, on an early Camaro or Chevelle, it’s not unusual for the stock front suspension to produce as much as 1.5 degrees of positive camber gain (or more!) as the result of severe front body roll. In other words, as the spring compresses, the top of the spindle angles outboard. This is counter-productive to good handling because what you really want is negative camber. So, by reducing body roll with a combination of a larger front sway bar and stiffer rate front coil springs, the positive camber gain can be minimized, which will usually result in the car exhibiting less understeer.
We’ve added a separate sidebar on alignment since any change to ride height or changes to the front or rear suspension can directly affect wheel alignment. This is a synergistic effect where a small change to one suspension component can have a major impact on vehicle dynamics. So, keep in mind that every time the ride height changes, or other suspension modifications are employed, these will also affect the alignment.
Performance Shock Absorbers for Muscle Cars
Without question, shock absorbers are another critical component that can improve handling. For most cars of the ’60s and ’70s, factory production shocks were tuned more for ride quality than handling and are not adjustable. For cars of this period, the available aftermarket performance shocks can be grouped in three different configurations: Fixed rate, single adjustable, and double adjustable.
Fixed-rate shocks, as the name implies, are not adjustable. The manufacturer determines rates for compression and rebound, which cannot be changed. Single adjustable shocks most often allow adjustment to the valving for compression, which is when the shock piston shaft is moved inward. Rebound is defined as movement of the shock as it is extended. Double adjustable shocks allow the tuner to adjust the compression and rebound separately, which is generally accepted as the best way to optimize handling, ride quality, or both.
Shock Absorbers
Without question, shock absorbers are another critical component that can improve handling. For most cars of the ’60s and ’70s, factory production shocks were tuned more for ride quality than handling and are not adjustable. For cars of this period, the available aftermarket performance shocks can be grouped in three different configurations: Fixed rate, single adjustable, and double adjustable.
Fixed-rate shocks, as the name implies, are not adjustable. The manufacturer determines rates for compression and rebound, which cannot be changed. Single adjustable shocks most often allow adjustment to the valving for compression, which is when the shock piston shaft is moved inward. Rebound is defined as movement of the shock as it is extended. Double adjustable shocks allow the tuner to adjust the compression and rebound separately, which is generally accepted as the best way to optimize handling, ride quality, or both.
Spindle Design
As mentioned earlier, most domestic cars of the ’60s and ’70s had front suspension systems that produced positive camber gain as they compressed. Some of this was the result of the relatively short spindles that were employed, which were usually paired with soft springs, allowing for major body roll that induced the positive camber gain. Just look at old road-test magazine photos of cars from that era being pushed hard into turns to see this effect in action—the body roll is downright scary.
In the early 1980s, muscle car chassis tuners discovered that a taller front spindle combined with corresponding tubular upper control arms could produce a desirable negative camber gain when pushed hard into a corner. This became very popular, especially with the GM A- and F-body cars. A one-inch taller front spindle combined with a tubular upper control arm could produce a negative camber gain that, when combined with a stiffer front spring rate, would dramatically improve handling. Another popular approach was to use a taller upper ball joint, which produced a similar effect without having to invest in custom spindles.
Muscle Car Rear Suspension
So far, this story has concentrated on the front suspension, but ideal handling must also account for what is happening at the rear of the car. If the rear suspension is too stiff, either because of a big sway bar or very stiff springs, this will cause the rear end of the car to break loose, most often on corner exit when the driver tries to accelerate out of the corner. Conversely, a rear suspension that is too soft will induce body roll, which can cause handling difficulties on corner entry.
Improving rear suspension performance can be even more difficult on vehicles equipped with rear leaf springs. This is because hard acceleration out of the corner generally requires a stiff rear spring to counteract spring wrap-up. But very often, a stiff rear spring will make the car oversteer both on corner entry and exit.
Snubber-type traction bars that may work great to counter-act spring wrap-up on the drag strip absolutely do not work in a handling situation, because when the snubber contacts the spring, the spring rate effectively becomes infinite, which is not good.
While we’re on the subject of the rear suspension, GM A-body tuners have also discovered that using tubular lower control arms is a great way to reduce lateral movement in the rear suspension, showing greater improvement than even boxed factory-style lower control arms. The tubular arms accurately locate the rear axle so that tighter tire-to-fender clearances are possible, allowing the builder to squeeze larger tires and wider wheels.
Rear Suspension
So far, this story has concentrated on the front suspension, but ideal handling must also account for what is happening at the rear of the car. If the rear suspension is too stiff, either because of a big sway bar or very stiff springs, this will cause the rear end of the car to break loose, most often on corner exit when the driver tries to accelerate out of the corner. Conversely, a rear suspension that is too soft will induce body roll, which can cause handling difficulties on corner entry.
Improving rear suspension performance can be even more difficult on vehicles equipped with rear leaf springs. This is because hard acceleration out of the corner generally requires a stiff rear spring to counteract spring wrap-up. But very often, a stiff rear spring will make the car oversteer both on corner entry and exit.
Snubber-type traction bars that may work great to counter-act spring wrap-up on the drag strip absolutely do not work in a handling situation, because when the snubber contacts the spring, the spring rate effectively becomes infinite, which is not good.
While we’re on the subject of the rear suspension, GM A-body tuners have also discovered that using tubular lower control arms is a great way to reduce lateral movement in the rear suspension, showing greater improvement than even boxed factory-style lower control arms. The tubular arms accurately locate the rear axle so that tighter tire-to-fender clearances are possible, allowing the builder to squeeze larger tires and wider wheels.
Other Things To Consider
This brings us to a slightly higher level of tuning, covering areas you might not think would contribute to handling, but in fact do play a part in cornering performance. Weight distribution is a very important factor. The reason the Corvette has a very long nose is to reposition the engine further back in the chassis to improve weight distribution closer to 50 percent front and 50 percent rear. For cars with the engine right over the front axle, like a Chevelle, weight distribution tends to land closer to 56 percent or more in the front, especially if the engine is an iron-head big-block. This makes it more challenging to improve the vehicle’s handling.
Other details that might seem insignificant include the choice of rear axle limited-slip design. A locker-style differential or a heavily biased limited slip, for example, will tend to make the car push the front end forward in a corner, inducing understeer. This can even be achieved by aggressive “cheating” on clutch-style limited-slip units. However, by changing to a gear-style limited-slip, like the Eaton TrueTrac, the car’s tendency to push into a corner can be greatly reduced.
Other details that will improve handling would be chassis stiffeners like subframe connectors. A weld-in subframe connector for cars without a full frame, like Camaros, Novas, Mustangs, E-body Mopars, and others, will improve handling by increasing overall chassis and body stiffness. Additional help can also come from a simple four-point roll bar.
Another aspect of handling is steering quickness. Older cars used relatively slow steering box ratios to reduce effort. But once you start down the path of better handling, it doesn’t take long to realize that a quicker-ratio power steering box is essential to matching the car’s ability to negotiate corners, especially if you get into the sort of tight courses found in autocross.
Everyone’s idea of ultimate handling will be different. Some will choose ride quality and comfort over pure handling while others will aim for the quickest way around a tight autocross corner. The beauty here is that, very often, both of these goals can be achieved with the same suspension approach with only minor compromises along the way. Regardless of your approach and goals, making suspension upgrades and tuning them for the desired performance will be a fun project that will transform any early muscle car into a machine that’s much more fun to drive.
Caster, Camber, and Toe Alignment Numbers
Front suspension alignments revolve around three factors: camber, caster, and toe. All three are critical and must work together to achieve a properly handling vehicle. Let’s quickly define each of these.
Camber refers to the angle of the tire as viewed from the front. Negative camber tilts the top of tire inboard, or toward the center of the car. Positive camber tilts the top of the tire in the opposite direction, with it leaning outboard. Improved handling is generally achieved with a slight amount of negative camber in the front tires with the car committed in a corner. Camber is expressed in degrees. Excessive camber, either positive or negative, will increase tire wear.
As we stated previously, most stock ’60s front suspensions tend to gain positive camber in a corner. This is called positive camber gain. For idealized handling, you generally want a slight amount of negative camber gain to plant the tire as it enters the corner. Adding negative camber to a static alignment will improve cornering but this comes at the cost of dramatically increased tire wear.
Caster is the next alignment angle. Positive caster is the tilt of the top of the tire/spindle rearward as viewed from the side. Negative caster is the opposite, with the tilt or the top of the spindle leaned toward the front. All vehicles benefit from positive caster. This improves high-speed stability, though it does increase steering effort. Any performance alignment will generally employ 4 to 6 degrees of positive caster. Caster is expressed in degrees.
Toe is the measurement of the angle of the front tires relative to the vehicle centerline as viewed from overhead. This spec is most often expressed in inches and either as toe-in or toe-out. If the distance of the leading edge of the front tires is farther apart than the trailing edge, this is toe-out. Toe-in is the opposite where the leading edge of the front tires is a shorter distance than the trailing edge.
A generic performance front suspension alignment for a muscle car will most often feature a ½ degree of negative camber, 3 to 6 degrees of positive caster, and around 1/16-inch of total toe-in. Keep in mind that even the slightest change to ride height (front or rear) will affect all three of these data points.
Sources
- Aldan American • (310) 421-0685 • aldanamerican.com
- BMR Fabrication • (813) 986-9302 • bmrfabrication.com
- Calvert Racing (CalTracs) • (661) 728-9600 • calvertracing.com
- Chris Alston’s Chassisworks • (800) 722-2269 • cachassisworks.com
- Coker Tire & Wheels • (866) 922-4139 • cokertire.com
- CPP Classic Performance Products • (800) 522-5004 • classicperform.com
- Detroit Speed and Engineering • (704) 662-3272 • detroitspeed.com
- Eaton (Detroit Locker / TrueTrac) • (800) 328-3850 • detroitlocker.com
- Global West Suspension • (909) 890-0759 • globalwest.net
- Heidts Hot Rod and Muscle Car Parts • (800) 841-8188 • heidts.com
- Hotchkis Performance • (562) 907-7757 • hotchkisperformance.com
- Lares Corporation • (800) 555-0767 • larescorp.com
- Lee Power Steering • (661) 568-9170 • leepowersteering.com
- Art Morrison Enterprises • (253) 922-7188 • artmorrison.com
- National Parts Depot • (800) 874-7595 • npdlink.com
- Original Parts Group (OPGI) • (800) 243-8355 • opgi.com
- The Roadster Shop • (847) 949-7637 • roadstershop.com
- Performance Suspension Technology • (800) 247-2288 • p-s-t.com
- QA1 Precision Products • (800) 721-7761 • qa1.net
- Summit Racing Equipment • (800) 230-3030 • summitracing.com
- Turn One Steering • (877) 468-8761 • turnone-steering.com
- UMI Performance • (814) 343-6315 • umiperformance.com
- Universal Vintage Tire • (877) 217-2553 • universaltire.com
- Viking Performance • (800) 236-6001 • vi-king.com
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