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­­Muscle Car Handling

by Mark Savitske

The pro touring movement has gotten huge, with upgrades to brakes and suspension becoming the most popular among vintage muscle car enthusiasts. Improving the handling and braking capabilities of these old cars comes with some challenges. Knowing you’re actually improving the car is chief among them! For those who really want to make a vintage American muscle car handle and stop like a modern car, the information contained on the pages of How to Make Your Muscle Car Handle is precious. All the modern options to update suspension and steering on vintage muscle machines are thoroughly reviewed. This excerpt gives a good idea what the book is all about.

Springs serve two basic purposes. The first and foremost is to simply hold up the mass of the vehicle. Without springs, the suspension would collapse and the car would drop to the ground. The second purpose is to provide resistance to the movement of that mass, vertically and in roll and in pitch. This movement and its velocity are further regulated by the shock absorbers. The shocks actually have more control over ride and handling than the springs, but you can’t properly select any shocks until you’ve chosen the springs.

Springs

The methodology used to select spring rates has changed quite a bit over the years. Older cars tended to use very soft spring rates (and soft shock-dampening rates), which was just enough to hold the car up at the desired ride height and no more. This was based on the presumption that such a combination would yield a soft and comfortable ride. But that’s only partly true.

The soft rates encourage the suspension to use a lot of travel, which does tend to soak up big bumps, but this travel also allows the car to wallow down the street like a small boat on the ocean. You can forget about performance handling as long as the car is pitching and rolling about like that. The problem is all of that suspension travel isn’t being used effectively and you’re getting a lot more reaction from the suspension than you really need. The new springs help tune this excessive motion out of the car. You only really need to use enough travel to make up for the imperfections in the road.

suspensionparts

Springs are a very important part of any suspension package, but they’re often misunderstood and misapplied. When in doubt, consult with a knowledgeable company that sells suspension parts specifically for your type of car. Ask questions and see if they match your intended application. You’ll usually have much better long-term gains with application-specific springs (like these from DSE) rather than a set out of a racing catalog.

Theoretically, if you have a 1-inch bump, 1 inch of travel should be enough to soak it up without making the body of the car react. Of course, a statement like that is leaving out a huge number of variables, but the point is you don’t need to use more travel than is necessary for a given circumstance. Some people’s first reaction when they make this realization is to go wild in the other direction, thinking, “If very soft springs make my car handle poorly, then super stiff ones should make it handle great!” So they buy the highest-rate springs they can find in a racing catalog and cram them in. Usually, no thought is given to the shock dampening rates, which become even more critical once you start messing with the spring rates. Does a car like this handle better than it did? Well, sort of; it corners flatter and dives less under heavy braking. But the car also feels much more jittery and unsettled. The ride quality could become downright poor, and its overall behavior somewhat stiff and erratic.

Consider for a moment that street cars and race cars live totally different lives and drive in very different environments. The race car only needs to perform well on the track for short periods of time, and at 100-percent maximum effort. Race tracks generally are smooth (yes, even Sebring is smooth compared to many public roads) and designed specifically for racing. There are usually gravel traps and large open grassy areas for runoff if you get a little too exuberant in the turns. 

A street car spends most of its time idling at stoplights, cruising at low speeds, just driving around, and going for a brisk run down a straightaway or through some twisting turns at, say,  60- to 80-percent effort from time to time. It may occasionally be called on to perform at 100 percent, but usually for a very short burst, then it’s back to tame driving again. No matter how ferocious the street car or how aggressive the driver, it still spends the vast majority of its time driving well below its maximum performance limits. The road conditions will likely run from decently smooth to rough and potholed. Turns are banked—not for best cornering speeds, but for the best water drainage. The runoff area may be a large tree, a concrete barrier, a parked car, or a drainage ditch. Things like this and a little common sense usually rein you in a bit.

Spring rates, like most other aspects of the suspension, have a point of diminishing returns where you get less performance gain and more tradeoffs for each increment of additional spring rate. Once again, more is not better; just right is better—always.

Spring Practice

So, what’s just right for a performance street car? Generally, it’s much harder to go wrong with springs specifically designed for your application. If performance street springs or performance touring springs are available for your car, then use them. This applies to coil springs, leaf springs, and torsion bars too.

However, just because you can get stiffer racing springs for your car doesn’t mean you get any more performance out of them. For your type of driving, you may get less performance, and you have to put up with a rougher ride too. The springs I recommend, in rate, generally perform halfway between vintage OE springs and road racing springs.

Performance street springs generally also lower the vehicle some advertised amount. That’s generally good because, compared to modern cars, most muscle cars sit rather tall in the saddle and have a fairly high CG. Lowering them helps overcome this issue and also generally improves the front-end geometry a bit. There are exceptions (such as C5/C6 Corvettes, whose geometry goes to the dogs when you lower them with springs), but for our purposes they’re typically a good thing. Lowering provides several gains: better performance, better stance, and, with the right change, better-than-stock ride quality too. And, happily, there are plenty of good performance-engineered springs out there to do  what you need without compromising anything.

Ride Height

I get more calls about this than any other spring-related topic. Everyone is worried about getting the stance of their ride just perfect, and rightfully so. More than trick paint or custom wheels, the stance of the car makes or breaks it. We all want it, but how do you get it? It’s not as hard as you think if you do your homework.

First off, don’t rely on the advertised drop of a given set of springs. “Drop” in relation to what—the car’s original factory ride height from 40 years ago? Do they mean before or after someone put some mystery springs in it in 1983? Yeah, drop is a pretty vague term. And if you can see that your car has old sagging springs, they may already be sagging as much as (or more than) the supposed drop the new lowering springs advertise. On the flip side, many replacements billed as stock replacement springs run much taller than true original springs. In this case, you could get a lot more drop than you were counting on.

Let common sense be your guide here. You can also reference original pictures of the cars to get a rough idea of whether your car’s current ride height is typical, higher, or lower than the norm. Weight also plays a big part in establishing ride height. 

Here’s a simple method to determine how weight impacts the ride height of a car: Start with the amount of weight you’ll be adding or (hopefully) subtracting. Let’s say you’re shaving off 250 pounds by swapping out your iron 454 for an aluminum LS2. You know your particular springs are 500 lbs/in. The 250 pounds you removed were shared by both front wheels, so each side sees a 125-pound savings. That allows a 500-lb/in spring to compress 1/4 inch less, which is not much. Now, apply the motion ratio of the spring as it’s mounted in the lower A-arm (I call it 2:1 because that’s fairly common) and you’ve got 1/2 inch of wheel movement, which translates to a 1/2-inch increase in ride height. An easier way to express it is to say 250 pounds is half of what is necessary to move a 500-lb/in spring 1 inch, so it moves half that much.

There are a several things you can do to help dial in your ride height. First, take into account any other variables that may come into play. Do you have dropped spindles? Are you using tall lower ball joints as part of a geometry correction package? Are you using aftermarket lower A-arms with non-stock depth spring pockets? Are your tires taller or shorter than stock equipment? Take all of these things into account and you won’t get blindsided by a ride height that’s way out there.

Next, with the car all together (that means everything—the grille, hood, antifreeze in the radiator, etc.), put the car on the ground, bounce it up and down a few times, and then roll it back and forth a little to allow it to settle to its lowest natural ride height. This is your baseline. If you chose all of your parts carefully (and you’re a little lucky) it’ll be right where you want it. If not, measure the car at several points and write down the numbers. This is your baseline height.

Finally, decide how much higher or lower you really want the car to sit. To simulate a higher ride height, just jack the car up until it looks right and measure it. When you compare the two sets of measurements you will have some idea how much you need to adjust the ride height to get it where you want it.

The easiest method to use with coil springs is to trim the springs to go down or add spring seat spacers to go up. Mopar guys are in luck up front, as they have adjustable torsion bars, which can be simply cranked up or down to get the desired height. Leaf springs can use different-length shackles and lowering blocks, which can be de-arched for less height or arched more for increased height. Each of these methods carries some caveats. Generally speaking, moderation is the key. Get close with the basic suspension/spring package and only use these methods to tweak it a little if necessary.

rearsprings

Rear springs must also be application specific, whether they’re coil-springs or leaf springs like these. Different companies use different methodology to select their spring rates, so it’s important to get your front and rear springs from the same source if you want optimum performance. (Photo Courtesy Detroit Speed and Engineering)

Upgrading a vintage muscle car’s suspension with some modern geometry and engineering will result in a car that not only handles better, but is much more enjoyable to drive and also much safer (because it’s more predictable). No other book covers the subject in the same depth as How to Make Your Muscle Car Handle. The movement toward pro touring is one that most industry insiders see expanding and becoming more of a standard than a trend. Making older cars safer and more pleasant to drive is just good sense, and understanding the subject fully is planning for the future.

 


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