Download as PDF, TXT or read online from Scribd. Flag for Bentley, Ross. Speed secrets: professional race driving lechniques/Ross Bentley. p. cm. . The most important factor is the driver, the ultimate control system of a race car. This book. DESCRIPTION Ultimate Speed Secrets is the driversâ€™ guide to going faster! Professional race instructor Ross Bentley has raced everything. Ultimate Speed Secrets is the drivers' guide to going faster! Professional race instructor Ross Bentley has raced everything from Indy cars to world sports cars.
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by Ross Bentley send me an email at [email protected] and let me know what you're going to need to check out my Ultimate Speed Secrets book. Editorial Reviews. Review. “Ross Bentley's Speed Secrets series of coaching books are a favorite around our office: they really help the driver to grasp what it. Read Ultimate Speed Secrets: The Complete Guide to High-Performance and Race Driving PDF Ebook by Ross Bentley. Motorbooks, ePUB.
A couple of notes on how to treat new tires. In this case, you may want to slide the car a little more, drive in the upper end of the optimum slip angle range to generate more heat in the tires to achieve maximum traction. This forces you to turn into the sl ide, or to "opposite lock," thereby increasing the radius of the turn. Traction" graph. If you find yourself having to back off the throttle after you begin accelerating in a corner, you must have applied the gas too soon or too hard in the beginning. Upcoming SlideShare. Sometimes described as "being in a four-wheel-drift," this is ideally what a driver is striving for when adjusting the handling of the car and trying to balance it.
Time your downshift SO that you have completed it, with your left foot off the clutch and over onto the dead pedal area, before you ever start to turn the steering wheel into the comer. When upshifting, for absolute maximum acceleration you need to know the en gine's torque and horsepower characteristics. With many engines you're better off shifting before reaching the reclline. You want to shift at an rpm that allows the en gine to stay in the peak torque range.
Engine RPM" grap in the accompanying il lustration. Assuming a 2, rpm spl it between gears an u. As the graph shows, from 5, rpm the torque curve is on a 22 decline.
However, if you shifted at 6, X rpm, the engine would be accelerating through the maximum torque range to maximum horsepower. In fact, an engine wi ll operate most effectively-resulting in the maximum accelerationwhen the rpm is maintained between the torque peak and horsepower peak. Notice r talk more about the engine torque than horsepower. As they say, "horse.. Talk to your engine bui lder, or study the engine dyno torque and horse power graphs to determine the rpm at which you should be shifti ng.
It makes a huge difference. When you are proficient at very smooth, welltimed downshifts, try skipping gears when downshifting. Instead of running through all the gears for example, from fifth to fourth, fourth to third, and third to second , shift directly to the required gear from fifth to second.
Obviously, this takes the right timing, using the brakes to slow the car, then downshifting just before turni ng into the corner. You must slow the car down with the brakes even more before dropping the two geal1i. This goes back to what I was getting at earlier-the less you do behind the wheel, the faster you will go. Every time yoo shift, there is a chance you may make a small error that will upset the balance of the car.
Shift as little as possible. In fact, the less downshifting you do while approaching a corner, the less likely it is you will make a mistake, and it wi ll be easier to modulate the brakes smoothly.
Now, with some cars, it seems the gearbox doesn't like it when you skip gears. Often, it is difficult to get a perfect match of the revs, therefore making it hard to get a gOCld, clean downshift without "crunching H it into gear. Obviously, with this type of car, you're better off not skipping gears. What about double- clutching? What is double-dutch- ing? Basicall y, you depress and release the clutch twice 23 fO each shift. The routine goes like this for a downshift: You then depress the clutch ped- al, move the shifter into neutral, release the clutch, rev the engine blipping the throttle using the heel and toe method , depress the clutch again, move the shifter into third gear, and release the clutch.
Your oo-. The reason for double-clutching is to help evenly match the rpms of the gear you are selecting with that of the engine to allow a smoother meshing of the gears. In a nonsynchromesh transmission, such as a racing gearbox, it may make gear changing easier. And that's why I say it may be unnecessary to double-clutch in pro- duction-based race cars with their synchromesh transmissions. But, if the synchros in your car's transmission are beginning to wear out, double-clutching can extend their life a little longer and make it easier 10 get it into gear.
You may be able to go racing for many years and never have to double-clutch. In endurance races, a driver may wanl to double-clutch to save wear and tear on the gearbox. At other times it is more a matter of driver preference. Another option with a pure racing gearbox is not to use the clutch at all when shifting.
This takes practice, as il is more crilicalthat the engine and gearbox revs are matched perfectly when downshifting. The advantage to not using the clutch is that it may save a fradion of a second on each shift. The disadvantage is that it usu- ally causes a little extra strain on the gearbox, perhaps vvearing it out a little sooner or risking a mechanical failure in the race.
Also, there may be more chance for you to make an error this way. Again, I think its important fO a driver to know hovoIto drive without the clutch-you never know when you're going to have a clutch problem and be forced to not use it.
More and more race cars are being built with sequential shifters. This is very much like a motorcycle shifter, in that the shift lever is always in the same position. You simply click it back to shift up, and fOlVlard to shift down. With this type of shifter it is impossible to skip gears on a have to go through all the gears.
Also, it may work better if you do not use the clutch. On an upshift, you just ease up on the throttle as you would with a normal gearbox , and click the shifter back into the next gear. On a downshift, it works the same way only you heel and toe blip the throttle as you click it down a gear.
Throughout my career, with most cars, I have usually used the clutch when shifting-single-clutching in sprint races and double-clulching in endurance events. I've found it puts less wear and lear on the gearlxlx. But when J started driving cars with sequential gearboxes, I found they shifted much quicker and easier without us- ing the clutch. It took a few lallS to get used to not using it-and to not being able to skip gears on downshifts. With a regular gearbox, though, I still prefer to use the clutch.
Chapter Chassis and Suspension Basics U nderstanding chassis and suspension adjustments and whal they mean to you as a driver is a critical part of your job. There are many good books Ihat deal with race car dynamics in great detail.
In Appendix B, I've listed the ones I think are mandatory reading for any driver. If you don't understand something, go back to these books or ask someone to explain it. If you want 10 win, you must know this information. I don't intend 10 go into great detail, but the following is a brief overview of some of the key areas of chassis and suspension adjustments that I feel you have to know to reach any level of success.
I really hope this piques your interest to go out and learn more. Camber Camber angle is the inclination of the wheels looking from the front or rear of the car. A wheel inclined inward at the top is said to have "negative camber"; a wheel inclined outward at the top has "positive camber. When a tire is leaned over, part of the tread is no longer in contact with the track, drastically reducing traction.
Therefore, the suspension must be designed and ad- justed to keep the tire flat on the track surface during suspension movement. Understand that as a car is driven through a corner, it leans toward the outside of the turn. This causes the outside tire to lean oulWard-more jX Sitive cambef- while the inside wheel tends toward more negative camber. Therefore, to keep the outside tire as it's the one that is generating most of the cornering force as flat on the road surface as JX Ssible, general ly the suspension is adjusted to measure neg- ative camber when at rest or driving down a straightaway.
Your goal in adjusting the camber angle is to maximize cornering grip by hav- ing the tire close to 0 degree camber during hard cornering. This can take a fair bit of adjusting and testing to come to the best static setting that will result in the op- timum dynamic camber angle. Castor Castor angle provides the self-centering effect of the steering the tendency for the car to steer straight ahead witnout holding the steering wheel.
It is the inclina- tion angle of the kingpin, or up4"ight, looking from the side. Positive castor is when the top of the kingpirv'up4"ight is inclined to the rear. Negative castor is never used.
However, the more jX Sitive castor, the more effort it takes to turn the sleering against this castor. There has to be a compromise between easy self-centering and heavy steering. Castor also affects the camber when the steering is turned. ThiS must be kept in mind when adjusting for the optimum camber setting. Per- haps, instead of dialing in more static camber, you may be better off adjusting In more castor. Remember, this will result in more negative camber on Ihe oul- side tire during cornering.
This can be an important factor. Learn and under- stand castor. Toe Toe can be either "toe-in" or "Ioe-oul. Toe-in is when the front of the tires are closer together than the rear; toe-out is the opposite-the front of the tires are far- ther apart then the rear. Toe can always be adjusted at the front, and can be ad- justed at the rear on cars with independent rear suspension.
Ackerman Steering The inside wheel of a vehicle driving through a corner travels on a tighter ra- dius than the outside wheel. Therefore, the inside front wheel must be turned sharper to avoid it scrubbing. The geometry of the front suspension is designed to achieve this. This is called Ackerman steering.
Some race cars have been designed, or modified, to have anti-Ackerman steer- ing. This means the inside tire is actually tumed less than the outside tire. The rea- soning is that the inside tire has so little of the cOfnering load that some tire scrub will not hurt. Both of these variations are designed to help the car's initial ''turn-in'' characteristics. Bump Steer Bump steer should be avoided.
This is when the front or rear wheels begin to either toe-in or toe.
Although it has been used to help band-aid a handling problem, bump steer generally makes a vehicle very un- stable, particularly on the rear wheels.
Antidive When you apply the brakes, the front end of the car has a tendency to dive. The suspension geometry is designed in such a way as to reduce this tendency. Generally, this is something designed into the car and requires--or even allows- little or no adjustment.
Antisquat When a car accelerates, the rear tends to squat down.
As with antidive, the suspension geometry is designed to limit this. And again, very littl e adjustment is required or avai lable. Ride Height The ride height is the distance between the road surface and the 10we. Often, this is different at the front than at the rear. This difference is called "rake"-usually with the front lower than the rear. Adjustment of the ride height, particularly the rake, is used to tune the handling. The ride height is usually determined by running the car as low as possi- ble without the chassis bolloming out or, at least, just barely touching on the road surface, or the suspension running out of travel.
Usually, the lower the 28 car is run, the better the aerodynamics; as well, the lower center of gravity is advantageous. Spring Rate The spring rate is the amount of force needed to deflect a sp! The diameter of the spring wire, the overall diameter of the spring.. Choosing the optimum spring rate is one of the most important setup fac- tors you'll have to deal with. II's your goal in developing the car to find the optimum spring rate for the front and rear suspension.
Generally, it's a com- promise between having a soft enough spring to allow the suspension to han. There are many more factors involved such as your drivi ng style or preference, the amount of aerody- namic downforce you are running, the weight of the car, the shape and con- dition of the track surface, and so on.
Perhaps most important, though, is the balance front to rear. Generally, it's best to use the softest spri ng possible on the rear-to help the rear tires achieve maximum traction under accelera- tion-then balance the handling with the optimum front springs. Wheel Rate The wheel rate is the amount of force needed to move the wheel a given amount, and is also measured in pounds per inch of deflection. It is determined by the geometry of the suspension and spring mounting location, and the spring rate.
Understand that even though you have the same sp! Antiroll Bar An antiroll bar sometimes wrongly referred to as a sway bar is used to resist the vehicle's tendency to lean during cornering. The antiroll bar, usually a sleel tube or sol id bar, is used to alter the fronl or rear roll resistance, affecting the car's handling characteristics.
Many cars have adjustment controls in the cockpit, so that you can compensate for changes in track conditions, fuel load, and tire wear duro ing a race. Adjusting the anti roll bars is probably the easiest and quickest change you can make to the suspension setup. Therefore it's important to try the car at full stiff and full soft settings to see what effect it has. As a general rule, to improve the grip on the front of the car to lessen understeer , you should soften the front bar or stiffen the rear bar.
To improve grip on the rear lessen 29 oversteer , you should soften the rear bar or stiffen the front bar. However, that's not always the case-as I 've discovered a few times-so be prepared to try the opposite.
When beginning to dial in the setup of the car, I like to do a Nbar sweep. That gives my engineer and me a good indication as to which direction we wi l l have to go to develop a good bal- ance in the car.
Roll Stiffness Roll stiffness is the total amount of resistance to the car leaning or rolling pro- vided by the springs and anti roll bars. This is measured in pounds per inch of spring travel at the wheel. This is primarily a function of the spring rate and the antirolJ bar stiffness. The distribution of the vehicle's roll stiffness between the front and rear suspension is called the roll stiffness distribution and is expressed as a per- centage front to rear.
Generally, it's the roll stiffness distribution that we use to fine-tune the handl ing balance of the car, using the springs and antiroll bars. Adjusting the front roll stiffness with springs or antiroll bars in relation to the rear, and vice versa, is the most common method of altering the handl ing bal- ance of the car. Shock Rate The purpose of a shock absorber is to slow down and control the osci ll ations of the spring as the suspensi on absorbs undulations in the roadway.
Actually, a shock absorber is a damper-it dampens the movement of the springs. Shocks work in both directions: A shock absorber, therefore, is rated by the rate of deflection at a given shaft speed, both in the bump and rebound direction. If the car's spri ngs are force sensitive, the shocks are velocity sensitive. You can also use the shock absorbers to alter the transient handling charac- teristics-how responsive the car is to your inputs.
If the springs and antiroll bars determine the amount of body roll and the distribution front to rear, then the shock absorber rates determine how quickly that body roll occurs. During the Indy Car season, we struggled with an understeer problem with the car. At pradically every race, the car would understeer in the early part of the corner-after I initially turned into the corner, but before I could get back on the throttle.
At Portland we realized that as J braked for a corner and the car's front end was heavily loaded, it would turn in very well.
But as J eased off the brakes it would begin to understeer. We ended up increasing the front shocks' 30 stiffness, both bump and rebound. This would help control the amount of nose- diving the car did under braking and then stop the front end from lifting back up so quickly as I eased off the brakes enteri ng the corner. As it turned out, this did- n't solve all our problems, but it was an improvement. So, the shock absorbers are another important suspension tuning coml Q- nent.
And, as with the spring rate, finding the optimum shock setting is a del icate compromise. It takes some experience before you have the sensitivity as a driver to be able to find that perfect setting. Corner Weight If you place the four tires of a vehicle on four separate scales, they will give you the corner weights of the vehicle. From there, you can determine the front-to- rear and left-to-right weight distribution, as well as total vehicle weight.
Learn to re,ld and understand shock dyne 8raphs and especially how their data relate to what you feel as a driver. For oval tracks, the setup will often be biased to one side or corner. Adjusting comer weights is one of the most important suspension tuning tools-one that is often overlClClked by many inexperienced racers. Tires One of the most effective ways of checking and optimizing chassis adjust- ments is by "reading" the tires. Evaluating tire temperatures will indicate if the tire pressures are correct, if the alignment settings are correct, how the overall handling balance of the car is, and, to some extent, how close to the limit you're driving.
All tires are designed to operate within an optimum tread temperature range. In this optimum range the tire generates its maximum traction as shown in the ac- companying illustration. Above or below that optimum range, the tires will not grip the track surface well. Also, if they are operated above the optimum range for too long, the tread may begin to blister, chunk, or wear quickly.
An average tem- perature range for a high-performance street radial is in the to degrees Fahrenheit area; for a racing tire, to degrees Fahrenheit. To determine tire temperatures you use a tire pyrometer, an instrument with a needle that is inserted Just under the surface of the tire's tread, generally at three points across the tire-the inside, the middle, and the outside of the tread.
If it's after a long straightaway or a slow cool-off lap, the temperatures may be misleading as part of the tread may have cooled more than others. II's important to take temperatures as close to a corner as possible. They must also be taken as soon as the car has come to a stop as they will begin to cool after about a minute. The optimum camber angle is indicated when the temperature near the outside of the tread is even with the temperature near the inside of the tread.
If the temperature near the inside of the tread surface is significantly higher than the outside, there is too much negative camber-the inside is heating up too much.
If the outside temperature is hotter than the inside, there is too much pos- itive camber. If the temperature in the middle of the tread is equal to the average of the in- side and outside of the tread, then the tire pressure is correct. If it's too hot in the middle of the tread, then the tire pressure is probably too high; too cool in the mid- dle and the pressures are low.
Ideally, Ihe tire temperatures should be even all across the tread. And if the temperatures on the front tires are even with the rear tires, then the overall balance of the car is good. The reverse is true as well.
If all four tires are not running in the optimum temperature range, it means one of two things: If the temperature is too low, you're not driving the car hard enough-you're not working the tires. If the temperature is too hal, you're driving too hard-you're sliding the car too much. More about this in the next chapter. Get used to reading a tire. If you can look at the tread surface in relation to the tire temperatures and how the car felt and then determine what to do to make improvements, it may make the difference between you and your competitors.
The surface should be a very dull black all across the tread. There should not be any shiny areas. If there is, it probably means that part of the tire is being over- loaded. Also, if you are driving the car hard enough-using the tires--the tread sur- 33 face will show a very slight wavy grained texture. It should be this s. A couple of notes on how to treat new tires.
When starting with a new set of tires, it is best to break them in. First scrub" them in by weaving back and forth if safely possible to clean the mold release agent off the surface.
And second, don't destroy them on the first lap by pUlling the car in huge slides through the corners and getting massive wheelspin under acceleration. In- stead, gradually build up the heat in them by progressively increasing your speed. Their overall grip will last longer this way. Q Race Car Dynamics -y-1"te more you understand about the car, the more successful you will be. Take the I lime 10 leam and fully understand everything you can about how the car works, how it is set up, and what each change should do and actually does.
Even if you don't work on the car yourself, being able to communicate what the car is doing to your mechanic or engineer is the only way 10 get the maximum performance from the car. As with many other aspects of racing.. In Appendix B, I've listed some additional books I strongly suggest you read.
Before making vasl changes to the car's setup, be sure that you first know the track well , are comfortable with it, and are driving well. I've seen drivers myself included gel so caught up in the idea of making the car work better, they forget about their own driving more about this in Part 3.
Also, when making changes to the setup, only make one adjustment at a time. If you make more than one, how do you know which one made the differencel I bought my first Formula Ford from a driver who had been racing for a number of years, and whom I knew was very knowledgeable about the setup and mechanics of the car. So I decided I wouldn't try to out-trick my- self.
I promised myself I wouldn't make any drastic changes in the car for at least the first season. I was just going 10 concentrate on getting percent out of the car as a driver, and only fine-tune the suspension. The second year I raced it.
Tire Traction In the last chapter we looked at the tires from the perspective of how they re- late to chassis adjustments. Now, lei's get back to how to drive them. In facl, to get the most from your tires, you rea ll y do have to understand them. You can be some- what successful in racing without knowing many of the suspension basics I talked about previously, but you must understand how tires work. Every force that affects your c,v, and your perl"onnance, is transmitted through the four tire;.
Ab50Iutely everything. So you better know how they work and be sensitive to! The first is the coefficient of friction between the tire and the track surface, which is determined by the road surface itself and the rubber compound of the tire. The second is the size of the surface of the tire that contacts the track surface-the contact patch. Obviously, the more rubber in contact with the road surface, the more traction available.
And the third is the vertical load on the tires. This load comes from the weight of the vehicle and the aerodynamic downforce on the tires. Sometimes it may feel like thai, but they al- ways give you some warning signs. As they reach their adhesion or traction limit, they gradually relax their grip on the road. In fact, primari ly due to the elasticity of the rubber, tires have to slip a certain amount to achieve maximum traction.
The term used to describe this ti re slippage in cornering lateral acceleration is called "sl ip angle" and is measured in degrees. As your cornering forces and speed increase, the tire ends up pointing in a slightly different direction than the wheel is actually pointing. The angle between the di- rection the tire is pointing and the path the wheel is following is the slip angle see the accompanying il lustration.
Street Tire , - - - -- '". Traction" graph. That range may vary slightly for different tires radial tires slip tess than bias-ply tires , but the basic characteristiCS remain the same. Up until that optimum slip angle range is reached, the lire is not generating its maximum traction capabilities. If the cornering speed or steering angle is increased, slip an- gie will increase along with tire traction until it reaches a point where lire trac- tion then begins to decrease again. How quickly the tire reaches its optimum range and then tapers off deter- mines the "progressivity" of the tire.
A tire that is too progressive one that takes too long to reach its limit and then tapers off very slowly is not responsive enough-it feels sloppy. A tire that is not progressive enough will not give the driver enough warning when it has reached its traction limit and is about to go beyond it-it doesn't have enough feel. This tire is difficult to drive at the l imit since you never know precisely when you're going beyond it.
A racing tire isiess forgiv- ing than a streeltire. On a dry track, maximum tradion--and, therefore, maximum acceleration, brak- ing. This means a tire develops the most grip when there is actually a certain amount of slippage. Fortunately, as I said earlier, when tires reach their traction limit and then go beyond, they don't lose grip completely, nor immediately. They adually lose grip progressively. And even when they are beyond the limit, completely sliding, they still have some traclion.
Think about it: Even when you have locked up the brakes and you are skid- ding, you still slow down-not as fast as when the tires are still rotating. The same thing applies during cornering. When the car starts to slide, the tires are still trying to grip the road. And, as they grip the road they are scrubbing off speed down to the point where the tires can achieve maximum traction once again.
This is a reassuring fact to remember-it's IXJssible 10 go slightly beyond the limit without losing complete control and crashing. We'll talk more about driving at and beyond the limit later in the chapter. Acceleration When accelerating, think of squeezing the gas pcdal-don'l pounce on II. Again, Ihe Ihrotlle is not an on-off switch. It should be used progressively; squeeze 38 it down and ease off it.
This must be done quickly, but smoothly. As I said before, there is a limit 10 your tire's traClion-approximalely 3 to 10 percent slippage on dry pavement, and somewhat less on wet pavement. Should the tires exceed this percentage of slippage, leading to wheelspin, it will result in less than maximum acceleration. At that point, simply ease off the throttle slightly, and Mfeather" it unlil you have controlled traction and maximum acceleration again.
Braki ng The braking syslem on most race cars is more powerful than any other system in the car. In other words, the car is capable o stopping much quicker than it can accelerate. Take full advantage of this. As with acceleration, maximum braking occurs with approximately 3 to 10 percent slippage. This means the wheels are actually turning slightly slower-3 to 10 percent slower-than they should be for any given car speed.
Exceeding this limit leads to lock-up-l00 percent sl ippage-and loss of steering control. Braking at the li mit or threshold of traction is called "threshold braking. This is what J mean by maximum braking.
Proper braking actually starts with how you take your foot off the throttle. As I mentioned earlier, do not lift off the gas pedal abruptly, but gently ease off the throt- tle--quickly! Then begin squeezing on the brakes, until you are at maximum brak- ing-threshold braking.
If you exceed the limit for threshold braking and begin to lock up, ease up slightly on the pedal; think of curling your toes back, feeling for the tires to begin rotating at the limit of traction again. In other words, you may have to modulate the pedal pressure slightly, using the feedback from the tire nOise, the forces on your body, and the balance of the car to achieve maximum braking. When approaching a corner, squeeze the brakes on smoothly, firmly, and pro- gressively. Then, as you reach the corner, release the brake pedal very gently as your foot goes to the throttle, so that you don't actually feel the point at which the brakes are fully released.
Remember, in chapter 2, I mentioned what made Jackie Stewart so successful. It was how he eased off the brakes. If you brake too hard and lock up the front wheels, you wi ll lose all steering Control. And if you do this, you will most likely "flat-spot" the tires.
This happens when the tires have skidded along the road- way and worn a patch of tire to the point where the tire is no longer perfectly round. You'll know exactly when you've done this-you'll feel a thumping or vi- bration in the car as the flat spot rotates. Practice braking when driving on the street. See if you can modulate the braJ.. Work on developing a real feel for the brakes; a very sensitive touch is important, espe- cially in poor traction conditions. You must be consistent with your braking.
Some drivers brake hard at the be- ginning and then gradually ease off slightly. Others do the exact opposite: The real key is to apply the same consistent hard braking all the way through the braking area. All else being equal, the two things that have the most innuence are the type of brake pad material and the amount of aerodynam- ic download the car is running. If you have a lot of rear wing in the car, you can apply the brakes very hard--especiall y at high speed.
If the car doesn't stop very well, the first thing to do is increase the rear wing. If it all goes wrong under brak ing and you don't have any confidence in the car, you will never be able to pre- sent the car 10 the corner properly. This then makes it almost impossible to get the car to turn consistently and onto the apex as you would like. Get the braking right, then work on the turn-in. For roadracing, you need a pad with excellent initial bite, with good modulation and release.
Some pads seem to 'self servo' and give the impression of either being 'rubbing speed' sensitive or too tem- perature-sensitive-when you first apply the brake, nothing seems to happen and then as the car slows down, the brakes seem to get better and better and you have to start reducing pedal pressure. This makes the car very difficult to drive. At most race meetings, there is very little practice time, so you don't want to waste time with a super sensitive pad that requires a lot of messing around with brake duct blanking..
Well, mainly because of the rules. All of these series prohibit the use of ASS, mainly as a cost-controlling measure. About the only use it saw in purpose-built race cars was in Formula One, where a couple of teams used it in and No verdict was reached on whether it was a major ad- vantage or a disadvantage. II was banned from the season on.
However, when ABS is standard equipment on a production Cilr, it is used on 40 production-based race cars such as the showroom stock class. Here, ABS can be both an advantage and a disadvantage.
It is a wonderful safety device, stopping a driver from ever being able to lock up the brakes. This is particularly useful in en- durance racing where ii'S more imjX rtant to be consistent and never flat-spot a tire. At the same time, ABS can be difficult to get used to and may be even a dis- advantage in racing. Often, a driver wants to "pitch" a car into a turn by going slightly beyond the threshold of traction on the rear wheels while turning into the corner. With ABS, however, this is not possible.
I once spent a couple of days testing a showroom stock Corvette. The first day it was dry, the second day it rained. Each day we ran with and without the ABS ac- tivated. In the dry I was half a second a lap quicker with the ABS turned off.
The next day, in the rain, I was over a second quicker with the ABS on. I really learned the pros and cons of ASS during those two days. It's important, if you're going to race a car with ABS, to get very comfortable with the feel of it.
Get used to the feel ing of the brake pedal pulsing and the in- ability to pitch the car into a turn with the brakes, as well as how hard you can- and have to-press the brake pedal. Slip Angle let's take a closer look at slip angles. If you noticed in the "Slip Angle vs. Trac- tion" graph, the peak traction limit, or lateral acceleration, is when the tires are in the range of 6 to 10 degrees of slip angle.
Our first driver is probably inexperienced, and definitely a little conservative. He consistently drives through the corners with the tires in the 2- to 5-degree slip angle range. As you can see from the graph, the tires are not at their maximum trac- tion limit. Driver I is not driving at the limit, and therefore will be slow. Driver 2 has a bit more experience and is known to be a little on the wild side.
He consistently overdrives the car. But what does that mean? Well, he always dri- ves through the corners with a slip angle above 10 degrees. In other words, he is sliding the car much. It may look great, with the car in a big slide all the way through the corner, but the graph shows that in this range, the tradion limit of the tires has begun to decrease from maximum. Plus, all this sliding about will increase the temperature of the tires to the point where they are overheated, further reduc- ing the traction capabilities of the tires.
Our final two drivers are consistently cornering in the 6- to degree sl ip an- gie range. Both are very fast. Both are cornering at about the same speed. Both are driving the car with the tires at the limit. So, what's the difference? Driver 3 is cor- nering in the upper end of the 6- to degree range-about 9 or while Dri- ver 4 is around 6 or 7 degrees. Again, the cornering speed is the same, but Driver 3 is sliding a little more than Driver 4, causing more heat buildup in the tires.
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