This is a reprint of John Brownes' excellent series of performance
articles that were posted to the BMW Digest a while back. Please
note that John retains full copyright of the articles and that
they are reprinted with his authorisation.
Posters, (to the Digest) including Scott Hung and Carl Buckland, have made intelligent and thoughtful comments on improving HP and handling. People like these two and others make this digest incredibly interesting and useful as technical information gets passed around.
It occurred to me that not everyone might understand how or why some changes affected your car. In particular, suspension changes are something of a black art that I know I spent years learning (and I'm still learning) about. I got to thinking that a little background might be helpful to some readers, and made me realize that one go-fast modification doesn't get discussed much on this list: the driver.
I further realized that there were a number of things I could write about, and so I decided to break it up into sections. In this part, I focus of making the driver faster. In the next part, I'll discuss how suspension changes affect handling, and why changing your suspension can make the car faster. In the third part-- well, I don't know if there will be a third part. Guess we'll have to see...
CAVEAT: All this stuff is opinion. I'm probably wrong on a whole bunch of it. All of it is true as far as I know. If you bother to read it, treat it like a grocery store: take the stuff you like and skip the stuff you don't. As always, I solicit your feedback, both positive and negative, and corrections of fact or alternate opinions. Your actual milage will vary. Not legal in California. See your doctor before beginning any exercise program.
First, however, I wanted to weigh in on philosophy of going faster. There are three kinds of "going faster":
1) Looking faster (the "showcar" mentality) 2) Going faster on the street 3) Going faster on the track
I'll leave the discussions of 1) for european car magazine, since they devote a large portion of their editorial budget to this type of car (cross-drilled brake rotors "for cooling (sic)" and trick shift-knobs).
Number 2) can be divided into two camps: stop-light warriors and the Mulholland Drive set. Stop light warriors want maximum acceleration: in short, they want their BMW to act like an American muscle car. Frankly, IMO, if you want accel, go buy an American car with a V-8. The Mulholland Drive set are the cafe-racers of the auto scene: they like to drive really fast in the twisties on public roads. The problem with that is that in an E36 M3, the to drive the car close to the limits requires speeds that are just too dangerous for public roads. I live in the foothills of the Cascade mountains here inthe sunny Pacific NW, and twisty roads are everywhere. I can drive at insane speeds without ever getting close to the limits of my car. It just isn't safe.... That said, making your car handle better (see 3) will make it more fun to drive quickly on the street.
Let's talk about number 3). First of all, there is a continuum from a totally stock car driven occasionally on the track (driver's schools) to dedicated race cars. At the one end, you have the car exactly as the Gnomes from Munich designed it: comfortable, safe, predictable. At the other end (the IMSA M3 race cars, for example), you have the car totally optimized for speed: uncomfortable, dangerous in less than expert hands, far less predictable. A car set up to handle ideally for an expert driver would be suicidal in the hands of a merely competent driver. Along this continuum is your car. Every substantive modification you make to your car (ie, shift knobs don't count) moves your car one way or the other on this continuum. The point you're aiming for is defined by your requirements (daily driver, AC, radio, backseat) and desires (lower lap times, winning BMW club races, etc). That said, there are three things you can do to make your car go faster:
1. Improve the driver. This is the cheapest and fastest way to more speed. Michael Schumacher could get in your stock 325i and beat everybody on this list around Laguna Seca in their modified M3s. There are lots of reasons for this which have to do with the strategy of attacking a track (knowing where to go fast and where to go slow), the learned ability to find the limits of a car and drive it there (did you see Herr Schumacher SLIDING his F1 on worn tires for fastest lap of the race after Alesi pitted at Monza?), providing the car with smooth inputs to prevent scrubbing off speed or upsetting the balance of the car, etc.
How do you improve the driver? Knowledge and practice. Knowledge can come from BMW CCA/ACA schools, professional schools (Russell, Barber), books and videos. Two books I highly recommend are Paul Frere (Sports Car and Competition Driving) and Alan Johnson (Driving in Competition): both classics. I read Frere (known to many by his work for R&T) in 1970 and it forever changed my driving style. Alan Johnson (multiple SCCA champion) described how to break the turns in a race track into three kinds, and how to order them by importance. Another key area of knowledge can be found in The Physics of Racing, by one of my co-workers, Brian Beckman. While physics can seem daunting to the non-technical, it's an important part of understanding vehicle dynamics, an understanding of which is necessary to drive a car at its utmost.
Practice takes seat time, pure and simple. It's not enough to just get out there and zoom around, if you're doing everything wrong. Lots of novices try to drive too fast too soon, and in doing so they learn some terrible habits that will be hard to unlearn. The best way to learn is to have a competent instructor providing feedback and guidance constantly. However, this is rarely possible, and lots of us find ourselves out on the track alone quite a bit. Here's some things I try to practice on track days:
- - Be smooth. If you can learn to be smooth, the speed will come later. Remember that fast laps are rarely the ones that look the most exciting. Pitching the car sideways in turns scrubs off tremendous amounts of speed. Slamming on the brakes unsettles the balance of the car. Every book and class on driving emphasizes this point: you have to be smooth. How to be smooth? Practice gently turning in to a corner, instead of trying to square it off. Try to get through the turn without making steering corrections. Your goal should be to drive through the turn by smoothly turning the wheel into the apex, then smoothly turning it back out to straight ahead. Everytime you make a significant steering input you scrub off real speed, as well as providing significant weight transfer. Squeeze the brakes and accelerator. When you shift, use your fingertips and shift slowly and gently. Getting excited and slamming the shift lever around won't help your laptimes or your transmission.
- - Practice consistent lines. There's lots of lines around a race track, and the one that works for the Club Fords might not be the one that works best for your 3200 lb M3. When you're just beginning, assume there are two: a dry line and a rain line. Have someone teach them to you, then practice them constantly until they are burned in your memory. Ideally you will have reference points set up for braking, turn in, apex, and track out for every turn. Sometimes at schools these will be cones; look for something permanent (a mark on the asphalt, fence post, whatever) that you can use after somebody hits a cone (I personally make it a goal to try to run over every apex cone set up in a driver's school: I don't do this maliciously, but I make it a rule to practice using EVERY INCH of the track; you'd be surprised at how many people don't).
- - Keep the car balanced. I used to hear this all the time, and wondered exactly what it meant. It means exactly what it sounds like: ideally you want the same amount of weight on each of the four tires all the time. Since you can't do that, except at rest, you have to constantly strive to stay as close to it as possible. In my next installment, I'll discuss how suspension setups affect weight transfer, but for now assume your car is totally stock. Try to visualize a scale under each tire as you drive. Braking causes the front tires to weigh more than the rear tires; accelerating reverses the equation. Braking and turning left causes the right front tire to weigh the most and the left rear to weigh the least. If you slam on the brakes at the end of the straight, the front end will become extremely heavy relative to the rear: the car will no longer be balanced. Squeezing the brakes results in less weight transfer, so the car remains more balanced. See how it works? One of the main reasons for smoothness is to maintain balance.
- - Use your vision. Generally when we learn anything new our vision is narrow and focused. With experience our vision becomes broader and more general. When you're first driving on a track you will look right in front of the car. Experienced drivers have learned to look up and out. They focus on where they want to go, not on where they are. You can't do anything about where you are, since by the time you see it you've already run over it. Look where you want to go, and the car will follow your eyes. Try this: when you reach the turn-in point, look at the apex. When you get to the apex, you should be looking at the exit or track-out point. Try to notice your peripheral vision as you drive; you should be able to see to the sides without moving your eyes.
- - Focus. Remember how super focused you were the very first time you drove a car? Later you probably didn't think anything of tooling down the freeway tuning your radio, chatting on the phone, drinking coffee. The more familiar something is, the harder it is to stay focused on it. Track driving is the same way. This is one of the reasons why intermediate and advanced drivers are more likely to have a shunt than novices, IMO. On a racetrack, the difference between a so-so driver and a great driver is concentration. Fortunately, this is something that can be practiced. As you brake, FEEL the brakes as they approach traction threshold. Focus: can you brake a little harder, or are you at the limit? As you put the power down out of a turn, focus: the car may oversteer--are you ready to counter steer? Sense the attitude of the car: can you feel a slight kick-out to the rear end before it's way out of sorts? Who's behind me; who's in front? Are they faster or slower? If the car in front spins, where am I going to go?
These are all things that I work on when I'm on the track, but they're also things I work on just driving around town. You don't have to drive fast to do this, you just have to practice. For example, try placing your tires exactly where you want them. Can you tell where they are? Can you just touch the edge of the pavement with your outside tires coming out of a curve? Can you come to a complete stop without the car rocking back? Can you shift (up and down, heel and toe) so smoothly that it feels like an automatic transmission? These are hard skills to develop, but fortunately they can be practiced on a daily commute, or driving to the store for milk. I practice them in all my cars, including my 6500 lb Suburban (ok, not heel and toeing).
Practice these until they
are natural, and you'll be a faster driver without spending a
penny on hop-up gear.
In our last episode we discussed how to make the car go faster by improving the driver (you!). In this part we'll delve into some technical details about suspensions: how and why they make your car go faster.
One of the reasons we bought BMWs in the first place instead of Camaros or Corvettes is that handling is important to us. At least, I hope so. And one of the things that BMWs do really well is handle. If so, why is it people like me and Carl Buckland are forever modifying our suspensions to get better handling?
Two reasons: to go faster and to have more fun. While it's true that races are won on the straightaways, it's also true that all other things being equal, the car that can get through the twisty bits faster will get lower lap times. As for fun, many of us like the responsiveness that a taut suspension gives our cars. We find them simply more fun to drive.
What's wrong with the stock suspension on my M3, you ask. Good question, Bucky. The engineers that designed your car had to factor in many goals in their design. First, the car must be safe. Since BMW can't make you pass adriving test before you get to buy your shiny M3, they have to assume that not all their customers are excellent drivers. Thus they design in some understeer so if you get in trouble the car will be more recoverable. Second, the car must be comfortable, so relatively soft springs and shocks are fitted to keep the ride quality high. Third, the car has to be competitively priced, so they have to select a suspension design and components that are affordable. Many other factors, from the size of the engine compartment, to ground clearance, ease of maintenance, and tire longevity have to be figured into the final design. Needless to say, that design, sterling as it is, is a compromise.
This year BMW will sell 100,000 cars, and most of them will still be running on a stock suspension 10 years from now. So BMW must be doing something right. For some of us, however, we want to optimize the design towards some specific goals. That's where modifications come in, and that's where it gets complicated.
For every modification to your suspension you make to improve handling, there's some tradeoff that comes along. Reduce the ride height and there goes your ground clearance. Pretty soon you'll rip some overpriced hunk of plastic off the bottom of your car as a result. Increase spring rates and ride quality goes out the window. Five miles of bad road and your tailbone will ache and you'll have more rattles than a 58 Nash American.
The other thing to consider when upgrading suspension components is exactly how the car will be different after you install them. And it will be different. It may handle better, it may handle worse. Read any article or posting about cars that have been modified and the authors universally rave about the better handling, turn in, predictable oversteer, etc. Rarely do they tell you that the car rode like a truck, darted all over the road, or plowed like a pig. All these things are possible and even likely if you start adding random suspension pieces without understanding the how and why.
One of the fundamental things that happens when a car corners is weight transfer. Basically the outside tires get heavier and the inside ones get lighter. Tires can handle lateral loads in proportion to their weight up to a point. So weight transfer to the outside means those tires can handle more lateral load (ie cornering force). Unfortunately, the inside tires give up more traction as they get lighter than the outside tires gain as they get heavier. So weight transfer results in deceased lateral resistance for the tires. This is a Bad Thing.
Although many people don't believe it, there are only two things you can do to alter side-to-side weight transfer. You can increase the track (width at the wheels) or decrease the center of gravity (CG). Weight transfer is a function of a triangle drawn between these three points at each end of the car. (Thus either end can have more or less weight transfer than the other end; this is an important point we'll come back to later.) You can increase track by going to wider tires to a certain degree, but typically body clearance prevents much change here. (This is why Porsche went to "fat" 911s awhile back, and why Ferraris are so wide). An easier way to improve the golden triangle is to lower the car, thus lowering the CG.
How do you lower the CG? Normally you put on shorter springs. That in turn reduces the suspension travel, ground clearance, and, on some suspension designs, increases negative camber, which is a Good Thing, unless it's excessive, and then it's a Bad Thing. Also, since the wheel travel has been reduced, the springs need to be stiffer to prevent the shorter suspension from bottoming out more often.
By reducing weight transfer, we have increased the total lateral loading our tires can accept, thus we have increased the maximum stead-state speed we can carry through a turn. For the purposes of this discussion, consider a constant-radius sweeper. The less weight transfer, the greater the speed possible before the car starts to slide. The car is more balanced side to side.
However, the car may be dramatically unbalanced front to rear. Ideally a car should have a 50/50 weight distribution front to rear, and the M3 is darn close stock. Changing springs won't change the static weight of the car, so even lowering it will retain the stock 50/50 dist. But as soon as you M3 starts to corner, the weight distribution changes. The car is engineered for understeer, remember? BMW engineers did (and you can) take advantage of linear (front/rear) weight transfer, which is a function of relative roll stiffness. The end of the car stiffer will transfer more weight to the other end. Thus if the front is stiffer than the rear the rear gets more weight transferred during cornering and thus "sticks" better. This is called understeer. (Sticks is a lousy word, because what actually is going on has to do with slip angles and force vectors. In reality understeer is when the ratio of the slip angle to the steering angle of the front tires is greater than the same ratio for the rear tires. But you get the idea.)
Roll stiffness can come from many sources: spring rates, shock damping, and anti-sway bar stiffness are the big three. Stiffening the chassis at one end or the other can also contribute (strut braces, etc). As you stiffen the rear relative to the front (or soften the front relative to the rear) the car will understeer less. The "ideal" theoretical setup is to have the car neutral: it neither understeers nor oversteers through our hypothetical sweeper. In reality drivers like to have their cars setup to do one or the other: I think I'll use part 3 to discuss why.
With so many variables (spring rates, ride height, shock damping (both rebound and compression), roll-bar stiffness... did I mention tires?) how can you possibly know what the "magic" combination is? The answer is there isn't one (stay tuned for part 3) but you can do some things...
Different schools of thought abound. One calls for stiff springs and soft roll bars. Others call for soft springs and fat bars. In general, I like the springs to be no stiffer than they have to be--one test is they should almost but not quite bottom out on the worst bump on a given track. Springs are critical in providing tire compliance: the ability of the tire to conform to irregularities in the road surface, rather than just bouncing over them. When your tire is in the air, it has no traction at all. Once you've settled on a minimum spring rate for each end, you adjust relative spring stiffness front to rear. Then you adjust balance with roll bars. However, that's just for racing. For driving on the street, you need springs no harsher than you can live with on the roads you have to drive on. Remember, too, that a swaybar is a spring, too: a torsion spring. The stiffer your swaybars, the more coupled the two wheels will be: ie when one is deflected the other wants to move as well.
One consideration people make (I went for it) is ride-height adjustable suspensions. Usually these are coil-overs with threaded spring perches. Coilovers are useful for two reasons: adjustable spring perches make it simple to change ride height, and the springs are sort of a standard diameter and size, and can as a result be found in a variety of rates. That makes it possible for a race team to tailor the spring rates to different tracks (more about that in part 3). Some coilover kits only allow height adjustment on the front struts; others allow adjustment at all four coners. The latter is preferable, since it allows you lower both ends of the car independently, and it also allows you to corner weight your car. This is the process of balancing the car from right front to left rear, and from right rear to left front. A car that is out of balance corner to corner will misbehave at times when you'd rather it didn't. It also lets you stagger the weights for a particular setup on a certain track. The principle is simple: raising the right rear increases the weight of the left front. Ditto. Vice versa. Etc.
Which brings us to the conclusion of Part 2: how the hell can you ever decide? You've got two choices. You can go with a "package" or you can roll your own. A package is a full suspension that you buy from someone, like Dinan or whoever. They've put together a combination of springs, shocks, and swaybars for a particular car that they believe work well together. As long as your goal for handling exactly coincides with the goals they established for a given package, it will suit you to a T. The alternative is to roll your own. You either start with a package and change stuff, or you just start from scratch and spec your own springs, shocks, and swaybars. This is expensive, time-consuming, and potentially dangerous when you try out your new setup on the track. The best way to roll your own is to do like the Big Boys: get as much adjustability as possible. If you have adjustable sway bars, you can try different stiffness without having to buy new bars all the time. That's where Koni shocks are better than Bilsteins: adjustability. Nobody's invented adjustable springs yet, but coilovers are as close as you can come. Typically you can go up or down in 50 Lb/in increments, which is pretty fine-grain.
We've covered a lot of stuff here, and I hope some of it's been useful. I guess in part I was prompted by ads I saw in magazines, and subsequent posts on the net, about different springs. These are generally advertised in terms of how much they lower your car (achieve the look you want!) which is a fairly meaningless metric. If you lower it a lot and get the CG way down there, that's good, but if you wind up with the balance all screwed up, or springs that are too compliant or too stiff, that's bad.
We haven't talked yet about
suspension alignment or tires. We also haven't talked about why a
car that handles great today may be a beast tomorrow. And why do
people care about tire temps? I'll try to cover that stuff next.
Ok, it's a sailing analogy, I admit it. We now return you to our regularly scheduled car conversation.
In our last epistle we talked about different modifications you can do to your suspension and how they affect weight transfer: both side to side and front to rear. To summarize a very long piece of mail ("Why didn't he just send the summary, Marge?"):
1. Side to side weight transfer is "bad" and we want to minimize it during cornering. 2. We can control front to rear weight transfer with individual suspension component selection/adjustment.
In this saga, we'll explore why we might not necessarily want a car to be neutral and why there's no perfect setup.
A given that most people understand, and that is widely and frequently quoted, is that understeer is better than oversteer. Is that true, and if so, why?
The short answer is that understeering cars are less likely to spin than oversteering cars. A more detailed answer requires us to examine human nature.
If you find yourself going into a corner too hot, whether on the street or track, what's your natural reaction? Your mind screams: TOO FAST and your right foot, which controls the speed of your car, immediately reacts by lifting. If that same foot is completely unenlightened, it might even step on the brake (hey, that's how you slow down, right?).
Bad call.
Lifting causes your car to decelerate, and deceleration causes weight transfer from rear to front. And that means the rear end is lighter. Lighter means the tires have less lateral adhesion available, so the rear end is more likely to break away as a result of turning forces. A fraction of a second later your view ahead is out the side window. This is not a good situation to be in. THIS IS AGGRAVATED IN A CAR THAT OVERSTEERS. By aggravated I mean that the car is more likely to do this, and with less effort to initiate it, than an understeering car. That's why Porsche 911s are for advanced drivers: follow your instincts in your 911 and the next sound you'll hear is your local body shop's cash register.
So almost all street cars are setup at the factory to avoid such a calamity. An understeering car will, UP TO A POINT, just plow the front end off at a tangent to the intended line should you be so foolish as to lift in a hot turn. Of course, even an understeering car can be made to spin (remember the Dukes of Hazard?). Classic American cars are famous for this, since 60-70 percent of the weight was over the front wheels and the cars had no ABS. Get on the brakes hard and whammo, the rear wheels lock and it's spin city. That's how the Dukes did all those lovely bootlegger turns. But that's at the extreme. Typically, if you're Joe Driver, you're in a little faster than you like so you lift. Nothing bad happens.
Of course, this is a terrible way to get around a race track. Let's look at two examples: a Club Ford and an F1 car.
The Club Ford has low horsepower, light weight, and skinny hard tires. Watch any CF race and you'll notice right away that the fast guys slide the cars through all the turns. Since the cars are not capable of generating high levels of lateral adhesion, the fast way through a turn is to oversteer the car through the first half of the turn, then power out. A typical CF turn, broken down, looks something like this:
1. Brake late
2. While still traveling too
fast to make the turn, ease off the brakes slightly and crank the
wheel
3. With the rear end severly
lightened, it will oversteer dramatically, rotating the car
quickly
4. Immediately get back on the
throttle, while straightening out the steering
5. Weight transfer from front
to rear, causing the rear to reduce the amount it's sliding
6. The lightened front end
begins to slide as well
7. Now the car is pointed
toward the apex, but aligned with the exit of the turn. If the
car went straight ahead it would drive over the apex towards the
corner workers.
8. However, the car ain't
going in a straight line. It's moving forward and sideways at the
same time. This is the classic, rarely performed by people who
say they have in their street cars, four wheel drift. It is a
thing of beauty to witness.
9. The car drifts out to the
exit of the turn, by which point it has lost sideways momentum
and is going where it's pointed again: down the track.
This is the secret to winning CF and FF and FV and such-like classes. Just watch a race and you'll see it. The guys in the weeds are the ones still learning how.
Now let's look at a F1 car. This car has high-horsepower, is light, and has wide, soft, sticky tires. It also has significant aerodynamic aids to create downforce when cornering.
Frankly I haven't a clue how to setup an F1 car. But my guess is that the drivers like them pretty neutral, with maybe a tiny bit of understeer. The cars are so fast that a loose car could get away from a driver before he could react. If you watch the in-car from F1 races, you'll see them cranking in opposite lock all the time though chicanes. That's not ideal, they're compensating for something that's wrong. The more you turn the wheel, the slower you go. Driving an F1 car sideways is not the fast way around the track. Those cars are in a very different league, because of aerodymanics. Those wings are designed to create downforce, which (because it increases loading) makes the tires stick better. (See? "Road hugging weight" isn't a total fiction, just a mis-statement.) As a matter of fact, 3Gs laterally is common. When the car has that much lateral acceleration, to have the tire let go means things will get ugly instantly. Only the truly great can drive such a car, and one of the reasons is from an old Carly Simon song.
Remember (I'm dating myself, I know it) Carly Simon's song, "Anticipation"? That's what keeps F1 drivers (and more normal ones as well) on the track. Generally in a truly fast car, you have to crank in inputs before the car does something evil. By the time the car is doing something bad, it's too late to correct.
Ok, are those guys psychic, or what? How do they know the car is about to do something evil? Here's where we get back to suspension setup. Generally the answer is that the driver needs a car which provides a lot of feedback, so he/she can feel what's going on. Knowing what to watch for as a signal that something is about to happen let's them anticipate their way out of trouble.
Here's a frinstance: as tire lateral loading increases, positive caster generates a ever-stronger self-righting force. That is, you crank the wheel to make a turn and the wheel wants to return to straight ahead. This is one of the advantages to having a lot of postive caster in your front end (there's also a drawback, natch). If you have power steering (here's where the 02 guys have an advantage) you can't feel that righting force clearly, because the boost overwhelms it. Why do we care about the righting force?
Because just before a tire starts to slide the righting force drops considerably, and a good driver will notice the wheel get "numb" and take corrective action. With power steering, it's really hard to feel that numbing in the wheel, if at all. However, the suspension has to have most of the micro-compliance (I just made up that term, don't go quoting it) removed for this to happen. Otherwise everything just feels kind of dead. Micro-compliance is the rubber in the bushings all through your suspension that keep a lot of road harshness and noise from intruding into your trip to Grandma's. Race cars use rock-hard bushings in place of rubber to get two improvements:
1) instant response to even
tiny steering inputs, since you're not wasting time/energy
compressing rubber bushings
2) total feedback from the
road.
So stiff springs and swaybars are the order of the day.
But not always.
What about when it rains? A wet track means far less traction available to the tires, so less lateral loading will be possible. In this case you want to be even smoother than before, and so lots of race teams will go with a "soft" setup, replacing springs, shocks, and swaybars with softer rates all around.
Sometimes what seems right just isn't. When BMW first started racing IMSA back in the 70s with those beautiful CSLs, they found in testing that high roll stiffness wasn't the fast way around the track. They went with softer and softer sway bars, with the cars rolling more and more, and kept shaving seconds off their lap times. Granted, these cars weren't exactly NYC taxis when they were done, but they _were_ a lot softer. Lap times never lie.
What about camber? Why is it important?
Take this test. Take a new pencil, hold the eraser to a smooth surface perfectly perpendicular, and attempt to slide the eraser. Now tilt the pencil slightly away from the direction of travel and repeat. Two things should become apparent: The harder you push down the harder it is to slide the eraser (duh!). A tilted eraser is harder to slide than a perpendicular. This is called the camber effect, and race cars typically want lots of negative camber (tires tilted in at the top) because of it. On older, bias ply racer tires, when the tire was loaded laterally with lots of negative camber it would actually lay flat on the road. Negative camber was added until tire temperatures, taken right after some hard cornering, showed even tire temperatures across the face of the tire. Modern radial race tires (like BFG R1s) distort differently due to the different construction method and thus won't show even tire temps across the face. All this tire temperature stuff is vitally important to race guys: you see crew workers show temperature slips to drivers during practice etc all the time. They learn a lot about their setup from temps and so can you, if you have a pyrometer.
Sadly, too much negative camber ("Marge, I smell a tradeoff coming...") eats up the inside tread of your tires from just diving around on the street. Lowering your car will induce negative camber, particularly at the rear, less so at the front. So before you buy those super-lowering springs you might want to think about what they will do to your camber.
What the really big guys do is to set up for a given track on a given day. Typically you'll optimize for a given section of track, since a setup that makes you fast through one turn may suck through another. Some turns are more important than others (see Alan Johnson's book, mentioned in part 1) so it makes sense to optimize for them over less important turns. This is why teams keep careful records about every time the car is on the track, track conditions, setup, lap times, tire temps, etc. Data acquisition for an Indy or F1 team is a serious business. As rank amateurs we have to do the best we can with a notebook and pencil. You also need to develop a feel for what the car is doing, and enough understanding of the components and their interrelations that you can figure out what changes to try.
Rule 1: never change more than one thing at a time. Change your tire pressures, or change your swaybars, but don't change them both and expect to learn anything useful.
As you get better and better, you'll want a car that allows you more control over its attitude (no, I'm not talking about "Yo momma") so you can rotate the car easily and point it where you want it. Until you get to Formula Atlantic and beyond, this is the hot ticket for getting a car through the tight stuff. It takes skill and lots of practice to master.
And the right suspension setup.
John Browne
BMW CCA
BMW ACA Puget Sound Region
M3 LTW (PeeKay)
Suburban 2500 (Godzilla)
326 iX (Spunky the brave
little car)
copyright © John
Browne; all rights reserved.
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