Smithology: Four thousand words about suspension
Hi! And welcome to an irregularly scheduled new feature we’re calling Sam’s Truth of the Week!
If the year 2020 has taught us anything, it’s that reality is a strange mix of undeniable fact and subjective interpretation. This is never more the case than when dealing with automobiles—machines that orbit a tantalizing blend of inarguable metrics and unquantifiable emotion. With that in mind, we’re going to occasionally use this space to nose into one of the truths in the realm. Expect to find here, on no regular or predictable schedule, a series of moderately focused digressions into various car aphorisms, plus a look at particularly compelling myths, legends, cartoons, drawings, carburetors, fuel injectors, books, movies, good new ideas, bad old ideas, a few deeply mediocre ideas, the engineering choices behind why new Porsche 911s no longer behave much like rear-engine cars, and, finally, the occasional abacus.
I was an English-Lit major in school, with a minor in Journalism. Call me stupid, but I love a good abacus.
I also love the frequently-asked-questions “FAQ” format of topic dissection. Largely because this is simply how my brain works when unpacking certain subjects—Question A leads to Question B, and then Problem C suddenly becomes apparent, so oh, hey, you start thinking about Item D, and that raises the notion of Digression E, and so on. So we’re going to use Truth of the Week to chase that format for a bit, see what happens. This process will be at least 40 percent more appealing than it sounds. Promise.
This week’s topic is simple. Consider the following five words:
You can be too stiff.
Roll that idea around in your head for a moment. (This is a family website, so keep it clean.) Lean into the notion. Imagine questions. Now imagine those questions on this page, in bold text.
In 3… 2… 1…
“Too stiff.” We’re still talking about cars on this website, right?
What brought this about?
A recent conversation with a friend on the subject of suspension tuning. Chiefly, we zeroed in on how so much of tweaking a car’s underbits can seem like a black art until you develop feel and learn a few things. We also discussed how the aphorisms in this corner of the business—ostensibly designed to simplify complex truths—can make absolutely no sense to ordinary people. Sometimes they don’t even make sense to a person who works in the space. Either way, these phrases get tossed around all the time, as if everyone understands them anyway.
Two examples are below. (Translated briefly, so we don’t compound the problem.)
1. We make street-car suspension stiffer to find grip, and race cars softer.
Translation: When chasing handling improvements, people often modify road cars by increasing suspension rate—“stiffening” various components. With race cars, on the other hand, you generally chase more compliance, not less. In either case, the goal is to run as soft a car as you can get away with, within reason. The difference is that most street cars start out much further, and much lower, from the goal.
2. Any suspension will work if you don’t let it.
Translation: Some suspension systems are simply so problematic in geometry that their motion generates more problems—usually along the lines of unwanted tire abuse from rapidly changing camber and toe—than it solves. These days, this problem is generally the domain of vintage cars. Either way, absent major modification, the best answer for increased grip is really to just limit compliance by throwing in gobs of suspension rate.
These aphorisms are fun to say, and they hold meaning. But those translations—generally as short as I could make them—are evidence of the larger problem. Suspension is complex stuff, and most ordinary people see it as a box of mystery. Even if they swap parts in their garage on weekends and spend their time racing or autocrossing or canyon-carving or whatever. (Sometimes especially if they do that.)
Neat! So where do we begin?
Think about it like this. A suspension has two jobs. First, it has to hold a moving car off the ground. That’s relatively easy. The second job is more complicated—properly presenting tire to pavement. The car has to hold a squared-off rubber-circle thing in a certain way as often as possible. Do that, and the tire will live something like its best life, behaving as its designers intended, providing a maximum of grip in varying conditions with a minimum of tradeoffs in noise, life, and so on.
Put shorter, the tire wants to see a gentle ramp into and out of the forces at work when a car brakes, turns, or accelerates. “Gentle” is relative here. Tires are like the surface of a balloon: They can take a remarkable amount of deflection and force, but they can’t take a sudden, concentrated amount of that same force. You want the car to squeeze the thing with fingertips, so to speak, not shove a safety pin into it. Surprise a tire, give it a sudden spike of load, and it breaks traction—even if that spiked load is significantly lower than the maximum the tire was designed to take.
Seems simple enough.
If only. You can’t have everything. This is where we hit the intangibles—the idea of balance, and the choices engineers make when designing and calibrating a car. Every suspension is designed and tuned for a certain balance between ride quality and performance. Some sacrifice grip in exchange for passenger comfort; others, vice versa. Some cars even trade grip for handling balance—letting go of all-out numbers performance in exchange for feel and a sense of cohesion.
Wait. Grip and handling. Didn’t you just say the same word twice?
No! Grip is grip—the amount of lateral adhesion a car can generate in a given corner, lane-change, wet slalom, whatever. Handling is a more general term, encompassing grip, transient behavior, and a host of other factors. Engineers use it to refer to how a car reacts to a sudden lane change on the highway, or how gracefully it recovers from a 130-mph drift in Turn 9 at Willow Springs. And a crazy volume of stuff in between.
No one car can do everything, gotcha.
Here’s the coolest part, though: A whole heap of cars—especially new performance cars—can do an awful lot of everything. And if you’re smart about it, you can, with a few mechanical changes, make your car do more of what you want and less of what you don’t. Most suspensions are made up of easily tuneable parts. Stuff you can remove and replace with aftermarket or factory components of different focus, higher resolution, or even just better quality. For the moment, we’ll focus on three of those components:
The springs hold the car off the ground and allow the suspension to meet changes in state—corners, bumps in the road, whatever—in a way that is both manageable by the driver and as comfortable and approachable as the vehicle’s original engineers and product planners deemed necessary. If your car had no springs, it would effectively be a skateboard: chassis bolted to wheel axle bolted to wheel. Skateboard over bumps equals: Ow, pain. Instant abuse to both tire and passenger. Bad for both comfort and grip.
The dampers help control the spring motion. Using valves, fluid, maybe computers, maybe even just a bit of friction, these components effectively calm the spring’s oscillations. Some people call these items shock absorbers, or shocks, though they do not “absorb” anything like a “shock” to the car. The easiest way to think about the job of a damper is to imagine a car sitting on uncontrolled bed springs: It would bounce and wobble around whenever something changed—turning, braking, weight transfer, a bump in the road, and so on.
The anti-roll bars mitigate body roll. In some cars, depending on additional hardware and/or design, they do other jobs. Some people call these sway bars, or stabilizer bars, though they do not control nor produce sway. (As for stabilization, that’s… vague.) Some vintage cars don’t have anti-roll bars, either by design or some quirk of trim or order spec. (Hell, some race cars have separate dampers in place of or in addition to anti-roll bars, or a fun monkey-motion linkage that accomplishes something of the same task. All fun trivia, but not important right now.)
Spring, damper, bar. The aftermarket generally views those three components as the immediately obvious variables—the first big changes you make when seeking handling gains. You can buy aftermarket versions of those components for just about any mass-produced vehicle, from Fox-body Mustangs and Miatas to workaday Volvos and Volkswagens. Most street cars can benefit from some increase in stiffness in all of these components: springs with greater rate; dampers with more restrictive or more complex valving; thicker anti-roll bars with perhaps more effective mount geometry.
There are other factors, though, you know? My cousin Frankie-Bob dialed the adjustable Koh-knees on my ’89 Le Mans to work real well with that front splitter I bought from PontiacSplitterCo.com. It’s got stanchions!
We will for the moment discount the complexity of active suspensions or tuning a suspension for aerodynamic concerns. Let’s stick to the basics. Frankie-Bob is probably pretty good, though. Who doesn’t love Frankie-Bob and the ’89 Le Mans? I love everybody. Never understood why Pontiac called that particular car Le Mans, though. It make you think of rural France like my toe jam makes me think of Usain Bolt? Any ’89 Le Mans people in the crowd? No? (Whew.)
I feel like you’re working up to a point. Just a hunch.
Correct! TL; DR: When most people modify a suspension, they almost always go too stiff. Too much spring rate, too much damper rebound or bump or [insert the many other damper variables changeable here], or too little bushing compliance.
If too much of those is bad, why does anyone end up there?
Because they initially seem to make sense. Because it doesn’t always feel bad. Because it can feel great, at first! All else being equal, the stiffer the suspension, the quicker the car will react to control inputs and state changes. (To a point.) If you’ve ever bolted on a set of performance springs or dampers, you know the deal: You turn the wheel, brake, or accelerate, the car’s reflexes seem sharper/quicker. Cornering can seem less dramatic. Stopwatches can show improvement on back roads and in a straight line. Either way, a lot of times, the car can feel more immediate—a more appropriate tool for your work behind the wheel.
That actually sounds pretty nice.
It is nice! The problem is the point of diminishing returns. With race cars, this point is relatively high; those devices spend most of their time on smooth surfaces, chasing lap times and working around a specific tire and driver goal. Their tires and aerodynamic aids generate large amounts of grip and often require large amounts of spring to manage. With road cars, or even dual-purpose track-street cars, that diminishing-returns point is a lot lower than most people think.
Stiffness in a suspension can produce a sensation of more immediate response, and in the right conditions, that response can help a car go more quickly. But it can also limit the suspension’s ability to react. It can reduce the window for driver error—or eliminate it entirely—when the tire begins to slide. And sometimes it’s just plain terrifying.
Fun thought exercise: With a bit of seat time, you can learn to tell, by the seat of your pants, when some of a car’s suspension bits are too stiff. All else being equal, all cars react in certain manner when traction is lost. Anti-roll bars help manage transitional response, so a “bar slide” caused by too much anti-roll stiffness is generally evinced by an icy and sudden loss of grip under abrupt transitions—the slide begins quickly once the car finishes loading into a corner or changing state. Too-stiff dampers (and there are a few ways they can be too stiff) generally give a tiny sensation of chatter in how the tire breaks, as if the rubber were skipping across the pavement on a microscopic level. Too-stiff springs generally make a car abrupt in limit response and overly sensitive in a different fashion, the tire seeming to “spike” into slip at the slightest delta from driver or pavement.
That’s all huge generalization, but you get the point.
Fun fact: In car-journo speak, the onomatopoeia for those slides are, in order, OOOOOOOOF, and AWWWWW, and HOLYDEATHBUCKETWEGONNADIENOW. Give or take.
Right. I care about road cars, though. If I’m sliding a car, something has gone wrong.
Race cars are not street cars in either function or form. They are, however, the purest version of an idea and generally the most effective answer to a simple engineering problem. The key is to remember that every car is a system. Racing or road, the bits work the same, as a system; each impacts the final result and depends on the other parts in the mix. All of which means you can use the same principles to chase both the edge of the envelope and appropriate compromise for ordinary driving.
Put another way, there’s a reason people love driving a Porsche 911, in spite of the fact that most folks lack the skill to whip-crank a 911 around a road course at the limit. Some of this is simple feedback; 911s make neat noises and fire-hose sensation, so you feel a part of the process. But the other half of the reason is the fact that Porsche engineers are among the best in the world at what they do. They actively work to make their cars forgiving and flexible at the limit, but also evocative and translucent below it.
I have had the great and insane fortune to have tested many of that company’s racing cars—934, 935, 962, 911s of all flavors—in addition to most of the marque’s production cars. Not for nothing have most of those machines been far softer in suspension, and far more forgiving, than you’d expect.
Wait. My cousin Eddie-Bob had an old Sixties Mustang. Didn’t handle for beans. We slapped bigger springs and stiffer shocks on it, and then it would run down his local back roads without plowing into a ditch at the first corner. After that, he took it autocrossing. We put even more gobs of spring into it, the big ones used by road racers. It was terrifying. Actually slower.
(Disclaimer: Someone actually told me this exact story at a club race at Mid-Ohio a long time ago.)
So much at work here. Race cars are sprung in response to spec sheet, job, and behavior, to begin with. Springs right for one tire and power output might not be right for another. Springs right for road racing may not work in autocrossing, or without a certain damper force curve. And so on and so forth. I’ve always been fascinated by the old-car problem, however. Vintage iron is inherently compromised and bad at certain jobs; this is part of why old cars are so much fun to drive. Next to new cars, old stuff makes you work more for less speed, and you often come away satisfied as a result, because you felt like a vital part of the process. You drove. You did something in which your efforts played a vital part. It gets really interesting, however, when you start expecting the behavior of a vintage car to line up with what its blueprint might suggest.
The intangible matters here. Some vintage cars use a seemingly unquantifiable and rarely predictable amount of chassis flex as an intentional design and suspension element (the MG TC comes to mind). In those cases, the inherent body or frame flex is part of the car’s charm and ability, and if you remove that, the thing will handle worse.
Hell, you can even tune into the limits of this stuff. In this country, many vintage race cars are required by rule to run on racing tires of modern design. Modern race tires have far more grip than period-style race tires, so people add spring to compensate. This is proper and works, but there’s a limit—you can eventually reach the point where the super-sticky tire and stiff spring produce such great load that the car’s shell becomes too much of a spring itself, waiting to uncoil at inopportune moment. Some vintage race cars will exhibit textbook behavior up to a certain point of high spring rate, then reverse the process as the chassis or tub flexes unpredictably.
That flex can play hell with suspension function and tire treatment. You can be at a point where the tire and suspension arrangement seemingly demand more spring for proper function—but more spring just makes grip decrease.
Certain vintage cars will let you address this problem with structural reinforcement. You strengthen (or completely tube-frame) the chassis, the progression goes back to normal, you add spring and the car behaves again. With some vehicles, no amount of added tubes will fix the problem, so you back down on spring rate, at the limit of available solutions.
Long story short: In the end, some answers just don’t fit your situation, and you work with what you have.
Holy wow, that’s a lot to unpack.
But it’s cool, right? The fun thing is, you can view it simply, and get decent results. Or you can view it on a granular level, and get great results. The key point here is: every variable matters. And the less seat time you have, the more those variables can muddy the waters of perception.
Among other things, a car’s handling both at and below the limit of a tire’s grip can be influenced by:
- Tire brand, compound, construction, wear, pressure, and age
- Differential type (open, passive limited-slip, locker, active/torque-vectoring limited-slip)
- Differential calibration and wear (how progressive, say, that a limited-slip is on ramp into and out of lock)
- Progression of engine power/gearing/delivery
- Alignment settings
- Suspension bind
- Driving style
- Road surface
- Weather and ambient conditions
And so on and so forth.
In short, a driver can think one thing is happening when it’s really another. This isn’t even getting into modern road cars, where stuff like torque-vectoring differentials and rear-wheel steering can make big cars feel like small ones in certain conditions, or simply band-aid a platform into doing something it couldn’t do organically, sans computing power. The effect is something like how certain military aircraft are inherently unstable and virtually unflyable on paper, but brought into stability by silicon helping the pilot. That military-aircraft thing is neat for a number of reasons, not least because it was once abnormal and now is not. These days, the practice is essentially the modern standard for high-performance flight.
Cool. So how do I learn any of this first-hand?
Easy: You read books, you drive stuff, you try certain modifications, you make mistakes, you build a mental reference book of what X feels like when Y happens. There are other ways in: watching videos online, for example, or playing with home driving-sim programs. Even just getting seat time in as many cars as possible, no matter how humble—if you’ve read certain books and have a basic idea of what to look for, the simplest of budget rental cars can tell you useful things about cause and effect in a vehicle’s suspension. The problem, again, is that although this stuff is complicated, it can seem simple. Because it also is simple.
That both makes sense and doesn’t.
When has anything worth doing ever been easy? And not to say that you can’t just slap some “sport” or “race” badged springs and dampers on your car and leave it at that. You’ll be fine, no one will cry, you’ll have a great Sunday on some back road somewhere and not have made a bad choice. Or you could pay attention to the details and get a car that works as best it can—the genius they talk about in magazines.
“Best” is a lazy word. Doesn’t mean anything. I thought you were an English major.
Translation: That car would be forgiving, comfortable, easy to drive quickly, easy to drive slowly, good on smooth surfaces, good on awful pavement. It would feel all of a piece and want to be your friend.
What if I just want to make my car faster and don’t want to learn any of this?
Good question! There is one answer that will no doubt, guaranteed, provide the greatest investment-return ratio for most people: You can simply find someone you trust, someone who knows this stuff, and ask them. This doesn’t mean forums or your favorite YouTuber. Chase the people working the science. Most reputable performance shops and tuning houses won’t want to sell you suspension without asking how you use the car. They will consider your answers, then help pick the answer that’s right for you. (If they don’t ask, don’t buy parts from them. They just want your money, not your future business.)
Wait, I thought this was engineering. Where there are hard answers.
Sort of. Yes. No. Maybe. Cars are funny that way. At least with regard to what the driver gets from the thing. There are hard answers to concrete problems in this realm, of course, but unless you’re dealing solely in lap times or numeric output, the perception of those answers is almost as important as the number. A quick anecdote before we wrap things up: Years ago, in another job, I was fortunate enough to test both a Mazda 787 Le Mans prototype and a Porsche 962 Le Mans prototype. Different days and tracks for each test, but same idea—one of those cars was Mazda’s 200-mph answer to winning the 24 Hours of Le Mans in the late 1980s and early 1990s, and the other was Porsche’s.
Both of those machines were intensely successful competition efforts resulting from countless hours of engineering and test work. Each car was the pinnacle of its company’s efforts in a certain arena, and each produced roughly the same pace around La Sarthe. The two cars couldn’t have been more different. The Mazda was cramped inside and loud, and extremely hard work to drive quickly. Its engine was peaky and narrow of powerband, and its suspension philosophy and dimensions made it exhausting at even moderate pace. The Porsche, on the other hand, was designed for a bit more comfort—torquey engine, wide power band, chassis less like a hand grenade and much more compliance.
Neither was by any means an easy tool in which to crank out a lap, but one of those cars was aimed at keeping the driver comfortable. Coincidentally, that car has a slightly longer stack of wins and endurance titles. Similarly, most tuner cars and SEMA specials have way more spring rate and boost than even Ayrton Senna could use. Go figure.
So the takeaway here is… think more and… learn about… suspension?
Always! Learn about everything! Learning never hurt anybody, right? But if I have given you nothing here beyond the idea that this stuff is neat, then we’ve all won and saved ourselves and become the true friends we made along the way. More takeaways: Don’t accept the standard answer to a question just because it’s the standard; verify for yourself. Find an answer for your life, not someone else’s. Eat your vegetables. Get a good night’s rest. Be kind to animals. Don’t order fish on Mondays. All things in moderation, as the old line goes—even moderation.
But generally, yes, you can make the suspension of any car far too stiff. Now you know.
Sam Smith is an editor-at-large with Hagerty. He came to the company after an eight-year stint at Road & Track, where he tested everything from Group C prototypes to Jack Baruth’s Plymouth Neon. He has always quietly wished that his full legal name contained a hyphenated -Bob.