[Editor’s Note: This article originally appeared in the December 2014 issue of Grassroots Motorsports.]
When Grassroots Motorsports came on the scene more than 30 years ago–back when it was called Auto-X magazine–the sports car world was facing sorry times. Famed brands like MG, Triumph and Austin-Healey had long left our shores, while Alfa Romeo’s Spider was still …
1. Road Course Skills
We know the Miata ushered in today’s golden age of sports cars. But what exactly is a sports car?
That simple question is a surefire way to start a lively discussion among enthusiasts. Passions will flair, expletives will be traded, and friendships may be taxed as opinions come to bear on this touchy issue.
The term itself implies that these cars will participate in some sort of sport. Since sports generally include a competitive element, a sports car could be defined as a vehicle suitable for some type of competition.
No arguments so far.
At this point, muscle car owners are feeling like part of the club. Drag racing is competition, right? Not so fast.
Here’s our first stumbling block: Subjectively, competition as it relates to sports cars should include left- and right-hand turns, with a few straights thrown in to let the brakes cool down.
Europeans invented the term in the context of Grand Prix racing on grand circuits–road racing, in other words. Sports cars were automobiles that could compete against one another, at some level, on road courses similar to those used by the ultimate racing cars of the day all over post-WWI Europe.
An enthusiast market was born, and cars began to emerge that were lighter, faster, sometimes quite basic, and available to the everyman. Then, after WWII ended, American soldiers returning from the war brought with them an appreciation for the sports cars they’d seen in Europe. The bug soon caught on in America.
All of this was before some Detroit ad men had a three-martini lunch and claimed the original Thunderbird as a “sports car.” Dilution of the concept began on our shores, let it be said.
So, a sports car began as a type of car somehow suitable for road racing–with or without modification–in stock form. This definition works well for the 1949 MG TC which, compared to the heavy sedans of the day, was a relatively athletic vehicle that out-cornered almost everything else on the road. It also works well for a 2015 Porsche 911, which can, in stock form, run hot laps all day on any race track in the world without turning itself into a molten pile of expensive rubber and steel.
Competition breeds passion, and this is where sports cars have us all in agreement. No 12-year-old kid sets an image of a Prius as his or her laptop wallpaper; it’s going to be a Ferrari, a Lamborghini, an Audi R8 or some other enticing, high-performance, worthy-of-passion car plastered proudly across the screen.
Sports cars stir something basic in a car enthusiast’s gut. My son said it the other night when we were cruising around in his ’95 Miata–nicely lowered to autocross spec. “Dad,” he said, “it never fails. Every time I pass a young kid in this car, he stares as it goes by. It never fails to stop them in their tracks.” I reacted the same way as a boy, drooling over brand-new Austin-Healey 3000s or Jaguar XKEs driven by happy, smiling men in our neighborhood on warm days.
So, a sports car must be suitable for competition and evoke passion. We’re all having a nice discussion so far. Now let me roll up my sleeves and start getting frank, at the risk of polarizing many of you.
3. Rear-Wheel Drive
Sports cars have to be rear-wheel drive. There, I said it.
I can speak with some authority as an experienced vehicle packaging engineer that front-wheel drive is never chosen for performance–unless you live in the Alps and drive on snow. Front-wheel-drive packages are chosen because a) they’re less expensive to manufacture, and b) because they optimize interior space for passengers.
Even if front-wheel-drive cars felt exactly the same as rear-wheel-drive cars in a 0.90g turn, this would be true. Of course, front-wheel-drive cars definitely do not drive or feel or handle the same as rear-wheel-drive cars, and the physics of why will never change.
Having opened this can of worms, I must ask that the all-wheel-drive proponents remain silent. You all drive mutants–very fast and enviously quick mutants, but mutants nonetheless, and we’ll discuss you another day. This is about traditional sports cars.
4. Two Seats
Sports cars also have to be two-seaters. Three is a crowd: You can only have a driver and a navigator/cop-spotter/friend/skilled mechanic in the passenger seat. No dead weight is allowed.
The goal here is to be quick and nimble. Four seats indicate practicality, and sports cars have performance as their paramount goal, not practicality.
I keep this as an integer-based argument, and I always round down: A Porsche 911 of any year has 2.7 seats at best, so it still qualifies as a two-seat sports car for me. No adult can sit in the second row of a 911 and say that it has rear seats.
I have been crammed into these vestigial compartments for dozens of cumulative hours in my life, only for the joy of getting to ride along in one of these great cars. I always had to weigh the pain of the seating position against the joy of being at speed in a 911. Passion always won out, and I have never been disappointed. So the 911 gets a bye in this case.
The Porsche 944 and 928 have 2.9 seats on their best days, but they’re also sports cars that nearly fall into the GT category. Porsche uses rear seats to evade German tax laws on two-seaters, so their heart is in the right place.
We’re getting into a gray area here, but this is why the third-generation Mazda RX-7 never came with rear seaty-things. Rear seats in sports cars are like Adam’s apples on women: They cause confusion.
5. A Stick Shift
Sports cars must have manual transmissions. Note that many of the new “shiftable automatics” actually function as automatic clutches, so there may be an argument for their inclusion. (They do shift faster.) However, in my mind, automatics (and auto-clutches) are unnecessary and expensive complications.
I want to double-clutch, heel-and-toe, and rev-match myself, thank you very much. ECU-controlled transmission shifting for a driver is like Auto-Tune for a singer: If you don’t have the talent, you shouldn’t have the microphone (or steering wheel) in your hand in the first place.
The final argument: Automatic transmissions can’t predict the future, and they never will. Case in point: When I’m barreling toward my favorite apex and need to bang against the rev limiter for three short cycles before I lift and hit the brakes, I don’t want the automatic shifting me into fourth. And it will, because it’s dumb and doesn’t read my mind.
I’ve seen automatics come a long, long way from the sad slushboxes of the ’60s, but they still don’t belong in a sports car. So, sports cars must have a stick with which to row the gears.
6. Less Weight
Sports cars must be lightweight. Dead weight not only taxes the engine, but more importantly the cornering ability of a car. It’s pure physics: It takes much more dynamic ability for a chassis–from the tires to the structure–to resist the centrifugal force of 1.5 tons of mass versus 1.0 ton of mass.
Lotus founder Colin Chapman knew this better than anyone. His famous recipe for speed was “Simplify, then add lightness.”
The Miata project, from the beginning, was known as our Light Weight Sports project. Simpler and lighter makes for better handling and cornering–surprisingly different traits.
Along these lines, sports cars must have good weight distribution. They have to be designed with handling in mind from the beginning. A 50/50 front-to-rear and left-to-right weight distribution is one of the holy grails of sports car design, and the packaging engineer makes the decisions that affect this outcome at the start of any project–long before the stylists start slinging clay.
A sports car’s powertrain, passengers and fuel tank–plus a host of other 20-pound parts–must be laid out carefully. Put these in the wrong places, and you’ll never make a vehicle work as a sports car. You can’t tune out poor weight distribution. Again, the Porsche 911 is the exception–years of development plus giant rear tires have trumped its poor balance.
The second-generation Lotus Elan is a different stoy. One of the most memorable quotes from Road & Track magazine was written in their review of the car, a nose-heavy, front-wheel-drive misfit from the very early ’90s “Lotus may have taught this pig to dance, but at the end of the day, they’ve left you dancing with a pig.” It handled poorly because there’s only so much you can do once you put parts in the wrong place. Balance is king.
7. Stunning Looks
Sports cars should be attractive–the more beautiful the better. Humans are shallow and find it easier to have passion for something beautiful.
Italy has always known this. Others, not so much. However, there is an honest, functional beauty even to the simplest of sports cars, including the Lotus 7 and MG Midget.
Some machines have played this the wrong way. We all know well-styled “sports” cars that don’t really live up to their promises. Sorry, but I put early Corvettes, the dearly departed Solstice, and its pimpy cousin, the Saturn Sky, in this group.
Beauty breeds passion at some very basic levels, but it doesn’t offset core faults. Brings to mind my home state’s motto: “Esse quam videri.” Look it up.
8. A View of the Sky
Sports cars should have a convertible top. Note the word “should.” The Lotus Exige, the Corvette Z06, the Ferrari 308–they’re all fantastic sports cars, but a convertible (or targa) top always makes them better, chassis rigidity notwithstanding.
Imagine if the Miata were only available as a coupe. What if the TR6 or Jaguar XKE only had rigid roofs? Less passion all around.
It’s not a fatal flaw if the top is welded on, but let’s face it: Roadsters are always more fun, and sports cars are supposed to be about fun. Final argument: Convertibles make you look cool.
9. Enough Power
In addition to responsive handling, a sports car needs to have a responsive engine with a reserve of power. Notice that I did not say tons of power.
The very ancestors of today’s sports cars were slow by any standard: There is not a classic MG produced that would break a 15-second quarter-mile. The same goes for most any Triumph.
What is necessary is a “good enough” power-to-weight ratio so the car can get out of its own way. The original Porsche 911 had only 18 or so pounds per horsepower. The second-best-selling sports car of all time, the MGB, had a power-to-weight ratio of 24:1. (We must live in great times, because today even low-dollar econoboxes can beat a 24:1 ratio.) In reviewing benchmark sports cars, we came up with the table to the right.
10. Enough Torque
More important than the peak horsepower–which addresses top speed–is torque, which makes acceleration. Back when we started the Miata project, we had to define just what a sports car was before we drew the first line. One question that came up was, “What cars are being restored by enthusiasts?”
The list that emerged was full of sports cars that inspired passion. These cars weren’t always the fastest or most powerful, but they felt great to drive. I love flooring the gas pedal on a ’67 Pontiac GTO. It’s a great way to recharge your testosterone, but driving one around at part-throttle is a bit of a chore.
A meager Austin-Healey Sprite in any gear around any corner is a hoot, regardless of throttle position, and that is what a sports car is all about. There is a saying that people won’t remember half of what you do, none of what you say, but 100 percent of how you make them feel. Sports cars make you feel something when you drive them. And that makes them memorable.
So, can we all agree that a sports car is a lightweight, rear-wheel-drive, two-seat, three-pedal convertible with great handling, good looks, a responsive engine, and potential for road racing? Make mine red.
How to Engineer the Perfect Sports Car
Now we have some parameters for defining a great sports car, but how do we turn them into metal, rubber and glass? Let me start out by saying that a sports car project is the highlight of most any automotive engineer’s career. (There are those who aspire to design minivans, but we Vaseline their keyboards when they’re exposed.)
Designing a sports car allows an engineer to get down to the core of performance in so many areas. The job becomes a labor of love. At last, the marketing doofs and accounting geeks are locked in a closet and objectivity rules. Capable engineers, equally informed, seldom disagree–the physics of vehicle dynamics rule the day.
The exterior designers (aka stylists) also have more freedom when it comes to sports cars. They’re better able to create a passionate shape for these projects than for, say, their mid-priced SUV assignments. Ugly is called out when it’s tried–no Aztecs sneaking through the system here. Beauty is the goal.
Giving creative and talented people a long leash can lead to brilliance in a product, provided the management will keep their hands off the finished work. The automotive world is peppered with some truly remarkable sports cars that were born out of the dreams of gifted men and women. In the best cases–think Porsches, Ferraris, Lotuses, etc.–the DNA for a performance car comes from all offices of the company, including the head office.
The paradigm of sports car design begins with eliminating as much of the unnecessary as possible. Think of an aircraft: Nothing comes on board unless it adds to the goal of getting aloft or staying aloft. Same for a sports car: Everything that is put into the vehicle has to have a purpose that is additive to the goal of taking a curvy road (or race course) at maximum speed. Every component must carry its weight, so to speak.
From an engineering standpoint, the priority list for a sports car goes like this: a light and rigid chassis, evenly distributed weight, a low center of gravity, optimal camber patterns, low unsprung weight, a strong engine, and good or great brakes. The particular order of this list may be juggled from project to project, but these are the components that make up a sports car’s soul.
Step 1: Win the Battle Against Weight
So, let’s start with weight. You’ll remember enough of your high school physics class to conceptualize the tension that would be in a length of fishing line used to hold an object as you spin it over your head. A tennis ball won’t break your 20-pound test line no matter how hard you spin, but a brick certainly will. It’s harder to get a heavier weight to travel around a circle than a lighter one.
Since we want our sports car to be superb around corners, lighter is better. No amount of tuning or shocks or tire technology will overcome sheer weight. This is one reason why the original Austin-Healey Bugeye Sprite was an amazing-handling car despite its average suspension design: It only weighs 1452 pounds.
Check out the column to the right to see some weights of representative sports cars, from lightest to heaviest.
At the very beginning of a sports car design project, the packaging/layout engineer will start with a driver of some proportion. This is typically a virtual mannequin representing the 92nd-percentile American male: 6-foot-2, 180 pounds, 32-inch inseam, 34-inch waist. For the Corvette, it’s probably the 95th percentile given the demographic, and for early Lotus 7s it was more like today’s 50th-percentile American male–before all those hormone-laden McDonald’s burgers hit the U.K., one can suppose.
This is no small point, since the driver is the single largest component that must be packaged, challenged only by the engine. Imagine how small a sports car could be if you didn’t need to fit all those pesky legs and torsos inside. Well, you’d end up with two Suzuki GSX-Rs bolted together side by side.
Once the engineers have packaged the part that makes the monthly payments–important point, that–they can work on fitting in all the other bits, such as the engine, transmission, driveshaft, rear differential, gas tank, radiator, steering column, and at least a heater core as a nod to comfort. The more tightly he can package all of these components, the smaller the structure that will be needed to support the weight.
One task of a car’s chassis is to hold all its parts off the ground–to serve as a kitchen table, as it were. Fewer components means less weight to carry, which means a lighter structure can be used. So for a sports car, options (used to be) limited. Triumph added air conditioning (begrudgingly) to the TR6 toward the end, but it was not pretty. Today, all mainstream sports cars have a/c as an option. We have become comfort divas, I suppose.
The limit to making a sports car’s structure light is that the chassis has to be as rigid as feasible. All the great suspension geometry in the world won’t mean much if the chassis flexes.
I had a friend’s Morgan over at my garage one day and jacked it up to change the left-front tire. My jacking point was on the frame, just behind the front wheel. As I lifted the front wheel off the ground, I noticed that the rest of the car was still sitting nearly flat; such was the flexibility of the wooden frame.
Driving that car was like sledding on top of a chest of drawers, squeaks and all. A lot of brain time goes into optimizing weight versus rigidity, but a sports car will be well served if optimal rigidity is a priority.
Step 2: Spread the Load
On the way to packaging all the important parts, a keen eye has to be applied to keeping the mass as low as possible in the chassis. The center of gravity acts as a lever against the suspension geometry–through the roll centers, which are not static–so the lower the mass, the smaller the lever. This reduces the torque acting to lean the chassis in a turn, making the tires’ camber less upset and resulting in a higher cornering limit. It’s intuitive: A lower center of gravity makes for a better-cornering car.
This leads us to the important decision of weight balance. Since we already have four wheels to hold up our chassis, it’s best if each one carries the same load. Four people, equally strong, can run fastest with a pallet of bricks if each one carries the same load. If two are carrying too much of a load, they will suffer and the other two will be coasting. Peak carrying capacity will be less.
The ideal sports car would have a 50/50 weight distribution on both the lateral and longitudinal axes. In my first layout for the third-generation RX-7, we put the radiators in the rear of the car as a way to balance out the mass of our front-engined package. In the end, that wasn’t necessary for the car to achieve the optimal 50/50 front-to-rear weight distribution–good thing, because rear radiators would have been expensive and problematic.
When the car hurls into a corner and its weight transfers to the outside tires, it gets complicated quickly. But in a steady-state turn–like on a skidpad–you want the two outer tires to be equally loaded. This takes balanced front/rear weight distribution.
Weight distribution affects more than just whether the car oversteers or understeers, as it raises the discussion of how fully loaded each tire is to its capability. Overloaded tires run at higher slip angles, and the discussion goes deep into tire dynamics pretty quickly. There’s the quick fix of larger tires that can be used to offset poor weight balance. (For an example, see the Porsche 911.)
Suffice it to say that having each tire carry the same weight keeps the dynamics pleasant and makes our sports car handle and corner better–handling equals feel, cornering equals ultimate g-force. This applies to front-to-rear and side-to-side weight balance. It’s rare that a car reaches the optimal 50/50 goal, but it is an important goal.
For the Miata project, we put all the heavy parts between the front- and rear-wheel centerlines, as do most sports car engineers. One item we lost out on was the battery: It started behind the passenger seat, an homage to my MGA which brilliantly used two 6-volts wired in series, one behind each seat.
In the end, the battery had to go to the trunk, behind the rear-wheel centerline (ouch), for structural reasons. To take the pain out of the compromise, we specified a special lightweight battery.
I take particular pleasure in what we discovered one day when we measured the corner weights on my own 1.6-liter Miata with hardtop installed, half a tank of gas, and 160 pounds of me in the seat. The Miata’s front/rear balance was 50.1/49.9, and its left/right balance was 51.0/49.0. The 20-pound supercharger on the left side of the engine threw us off of perfection on each axis, but it more than carried its own weight. (You can never be too light or have too much power, as they say in racing.)
I’d be remiss if I did not mention one of the best (and most underappreciated) vehicle packages ever accomplished: the Porsche 914. All significant weight is between the wheel’s centerlines and low, low, low to the ground. There’s a spacious interior and two trunks, with room for a rigid Targa top in the rear trunk.
Study the packaging of this car to see what some of the best engineers in the world at the time came up with. It is a thing of engineering elegance on many levels.
The Lotus Europa and Esprit are probably the two best-handling cars ever built, both being lightweight with superb suspension designs. All three of these examples are mid-engined cars, something to discuss another day.
Step 3: Keep the Rubber on the Road
It’s a pretty basic concept to grasp: The tires have to stay in contact with the road to achieve any traction in a corner. The gremlins that spoil keeping the contact patches solidly planted reside in the suspension design.
A sports car engineer gets all sorts of coupons with the other design teams when it comes to suspension design: Mess up this area, and the car will be laughed off the pages by journalists. If you’re calling a car a “sports” car, it’d better perform well against the competition in the twisties.
We talked a bit about how the center of gravity works against the suspension’s roll centers to force the car’s chassis/body to lean in a turn. Some lean is inevitable, and each degree of lean causes the tires to move away from perfect alignment (camber-wise) to the pavement.
Numerous books and Ph.D. papers have been written about this subject, but we can summarize it by saying that a tire likes just a bit of negative camber when it’s forced into a turn. Why? Because as the tire is distorted by the variety of forces acting upon it, negative camber keeps its tread portion in optimal contact with the road.
Of course, making a suspension perform this feat costs money in the form of special linkages and mounts. It’s a lot easier (and cheaper) to throw in a solid rear axle, but the camber is always 0 degrees with one of those–unless you get creative with a torch, which can be done.
A semi-trailing arm is a step in the right direction (thanks, BMW, for popularizing this design in the ’70s), but they sometimes cannot achieve aggressive enough camber gain to compensate for body roll. Same goes for MacPherson struts, which are chosen for their cheapness and ease of packaging. They’re mostly found in the front ends of imports with creative variations, but they, too, mostly have limited camber gain during compression.
The fixes for this are to use massive static negative camber at rest and to use stiffer anti-roll bars to reduce the “camber loss” during cornering. But these are mere patches.
The clean-sheet-of-paper sports car engineer wants to use uneven A-arms or some variation on that theme to get the camber gain desired without breaking the bank. It would take another article to do this discussion justice. Let’s just agree that the suspension needs to be independent at all corners, and has to have aggressive camber gain to keep the tires aligned with the pavement in an optimal fashion during hard cornering.
Exceptions abound. We cited the Sprite and Lotus 7 for being excellent sports cars, and both have solid rear axles. See what being lightweight does for you?
There are dozens of other criteria for a sports car’s suspension to discuss, some of which include low unsprung weight, toe-in and toe-out behavior of each wheel during braking, accelerating, engine braking, etc. The overall goal is to achieve both high cornering limits and a certain seat-of-the-pants feel for the tires’ contact patches.
It’s a complicated formula that car companies don’t always apply well. Lots of parts can be assembled and you end up with a Stepford wife-type of car–no passion. Legendary sports cars communicate their own zeal.
How a car feels involves many components: How the steering responds to your input, how the body leans over when thrown into a corner, how the engine revs (or doesn’t) when goosed, how the brakes feel, how the brakes upset (or don’t upset) the chassis when applied mid-corner, how the vibrations from the suspension telegraph what’s going on at the road surface, etc., etc.
The car has to fit like a glove and deliver a real connection to the driver. Mazda’s oft-repeated “oneness between horse and rider” tagline was not a marketing department concoction for the Miata. It came up at a brainstorming dinner at the beginning of the project, when we were discussing what the perfect sports car would feel like. Great sports cars have an almost telepathic relationship with the driver’s will. They nearly anticipate the next move.
Soul: The Secret Ingredient
A sports car in its final form has to be like your favorite song, the one that begs you to reach over and crank up the volume knob every time it comes on. The car has to evoke a passionate response from its driver.
How do you make a bucket of bolts do this? It’s a combination of purposeful choices, careful development, and uncompromising stubbornness on some key points we’ve discussed.
Just when does the soul get put into the design? At the very start, my friend. At the first glimmer in the engineer’s eye. Otherwise, all is for naught. No matter how hard you try, you can’t fake passion in a project like this.