Ultimate Autocross

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Damper Designs

There are three basic designs of shock absorbers: twin-tube hydraulic, twin-tube low-pressure gas, and monotube high-pressure gas. Each of the three has its own abilities and functions, and you will find all three in street or street-derived racing applications.
One of the most common misconceptions is that a gas shock is filled entirely with gas and no oil. In fact, all three designs use hydraulic oil-they just may have a nitrogen gas charge pressurizing the oil in the shock.
The twin-tube hydraulic, as the name implies, has two cylinders (or chambers) and no nitrogen. The inner cylinder is where the rod and piston live and work, and the outer chamber is a reservoir for oil and air. As the rod travels in and out of the inner cylinder during stroking action, it displaces oil from the inner to the outer cylinder, then draws it back inside. Although this is the oldest of the three designs, it still maintains certain benefits and has a place in performance damping.
The twin-tube low-pressure gas shock is much the same as the hydraulic, except that it has a low-pressure nitrogen charge (usually 5-15 bar/70-210 psi) in the outer chamber, instead of an air pocket. Some manufacturers seal the nitrogen in a plastic bag, while others will allow the nitrogen in solution with the oil.
The original theory behind placing the nitrogen inside was that it would put the oil reservoir under pressure and therefore raise the oil's boiling point, reducing the tendency for heat-related fading or foaming as it passed through the valves. That really isn't much of a concern today as the quality of oil has increased in performance dampers. Plus, modern performance shock design has moved away from needle valves and o-ring seals that are affected by heat and viscosity changes, and most street cars and many race cars simply will not generate enough heat to challenge the oil in a proper performance shock.
However, when the nitrogen gas is in solution with the oil, it can give the added effect of damping really minute harmonics and motions that otherwise would not be big enough to make the damper's piston move.
The final design is the monotube high-pressure gas shock. The monotube's entire body serves as the chamber; this allows for a larger piston area, and therefore it has the ability to transfer more damping information over a smaller stroke area. Displacement of oil by the incoming rod is handled by a chamber at the bottom of the unit that contains a high-pressure nitrogen charge (20+ bar/ 300+ psi) and is separated from the oil by a floating piston.
Each design offers certain advantages and disadvantages, so the best choice will depend upon the intended application.
A twin-tube design, when compared to a monotube, has a longer stroke capability and greater oil volume in a similarly-sized unit. Therefore, the twin-tube will tend to give a smoother or more forgiving ride characteristic and still supply the firmness for proper handling control in vehicles that see average or long suspension stroke length.
The larger piston area of the monotube will give more control over much shorter stroke lengths or at the lowest piston speeds, but also tends to ride more harshly for exactly the same reasons. In racing applications where heat generation is more likely to be a factor, a monotube can cool itself more quickly because the shock body is the wall of the working cylinder.
You are likely to find monotubes on non-production-based race cars (formula cars and such), where control over very short strokes is mandatory and ride quality is not an issue, or on production-based race cars where once again control is more important than ride quality. Most of the rebuildable, high-end race shocks will use a monotube design.
Note that gas pressure in the shock can extend the oil's heat tolerances, but can also affect ride height because the greater pressure can act as a slight booster to the spring rate. Cars that run lower spring rates don't want the boost, so they usually use hydraulic shocks or must be willing to compensate for the gas pressure.
Monotubes can also operate while mounted on their side or at any angle, so they are more conducive to racing pushrod suspensions, while twin tubes must operate from upright to no more than 45 degrees from upright (which is still fine for most production-based suspensions).
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Before You Call

So let's say you have decided what vendor to go with and you have credit card in hand; now what do you do? Before calling, Danny Criss from Leda recommends you have at a minimum the following info on hand: vehicle year, model and use (street, road race, rally, autocross, etc.).
If the shocks are for a competition car, he also recommends being aware of any limitations set forth for that particular series. While the general trend in racing has been a loosening of the limits set on shocks, you're still better off knowing what you can and cannot run before making any financial commitments.
Retailers need to know the true use of the car, stresses Jay Morris. "No Walter Mittys allowed except for the Walter Mitty Challenge. No retailer likes to field complaints from customers who said they were going to go through drivers school and never did." Morris adds one more caution for prospective customers who may still be coming to grips with reality: "We also need to know how much room you have left on your credit cards."
If the car is a purpose-built car (vs. a production-based race car), there is some other info the shock builder will need, points out Penske's Jim Arentz: "Make and year of car, type of racing, inner spring diameter, spring length, needed bump travel, fully extended length of existing damper on car, number of adjustments desired, and type of chassis mounts."
From the info you provide, the shock company should be able to hook you up with the right shock. "The tuner should be able to calculate natural frequencies (or recommend spring rates) and a good guess at the damping characteristics, while on the phone," explains Shocktek's Michael O'Callahan. "Note that this information should not be a guess out of the blue, or from 'experience,' but should be based on the physics of automotive suspensions."
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Rebuilding What You Have

Many of us can't afford to buy new shocks, but we would still like to improve our chances of winning. Upgrading your present shocks may be an economical way to vastly improve your car's transient handling characteristics and bump control.
For instance, if you bought off-the-shelf Konis or Bilsteins, you can have the internal valving modified so that it reacts more quickly or offers more resistance in bump or rebound. Koni shocks that initially came with only adjustable rebound can be upgraded to double-adjustable specs (both adjustable rebound and bump). Likewise, Shocktek can convert non-adjustable Bilsteins to either single- or double-adjustable specs.
This can be done at a substantial savings when compared to purchasing new shocks. At the time of the upgrade, you could also have the valving modified to suit your specific type of racing. Autocross shocks would be valved differently than road race or drag shocks.
Having your shocks upgraded is good, but just as in purchasing, be cautious. This work should be done by factory-trained personnel (who have access to a shock dyno), and hopefully by someone who also understands the type of racing you do. Look for references and look for the reputation the company has within your racing circles.
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Anti roll bars

Lean Less

The inside scoop on anti-roll bars

story by john comesky

Any enthusiast worth his salt knows that ires have arguably the biggest impact on a vehicle's handling. Obviously, however, there are chassis dynamics that extend beyond the realm of tires. Once you increase the traction threshold at the road surface, then you may be ready to take the next step into improved vehicle handling: reducing body roll through the use of anti-roll bars.
Properly chosen (and installed), anti-roll bars will reduce body roll, which in turns leads to better handling, increased driver confidence and, ultimately, lower lap times.
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What Is Body Roll?

Chances are, you've experienced the effects of body roll every time you're behind the wheel. It happens during almost every turn when one side of the car lifts, causing the entire vehicle to lean toward the outside of the turn.
The cause of body roll is simple physics: An object in motion tends to stay in motion until acted upon by an outside force. So in practical terms, as you drive ahead in a straight line, you're allowing a couple of thousand pounds of vehicle, fluids and passengers to build momentum in that straight line.
When you tell everything to change direction suddenly, through input at the steering wheel, the front tires may change direction thanks to the mechanical advantages of the steering system, but the momentum of the vehicle, fluids and passengers continues in the original direction. The tires are the only element capable of generating an outside force that can act against this momentum and change its direction.
At this point, one of two scenarios is most likely to occur. If enough momentum exists in the original direction, and the tires lack enough grip to act against the original forward energy, then the vehicle will slide out of the turn as the tires lose traction. However, if the tires have enough grip at the road surface, then instead of sliding, the vehicle's traction at the road surface will overwhelm the original forward momentum and act upon the original forces to induce a change of direction. Hence, a cornering maneuver.
But what happens to that energy? Even though we may have had enough grip to hang on through the turn, we know that the momentum of the vehicle mass will continue in the original direction. The result is a weight transfer toward the new outside edge of the vehicle-the same direction as the original forward momentum.
If enough energy is behind the weight transfer, then this energy will cause the outside suspension (in this case, the spring and strut assembly) to compress while the other side lifts and extends. An engineer type likes to describe this by saying that one side moves into jounce while the other moves into rebound. The rest of us call it lean or body roll.
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Why Is Body Roll a Bad Thing?

We often hear that preventing body roll is "so important" that we must all rush out and buy this product or that product in order to prevent it. And many enthusiasts have consequently accepted that body roll is therefore bad. But what exactly does body roll do to negatively affect vehicle handling?
For starters, it disrupts the driver. This is probably the effect that most drivers can see and feel during their own driving experiences. And while this is not the most important negative effect of body roll, it is true that the car does not drive itself-no matter how many aftermarket parts you install. So keeping the driver settled, focused and able to concentrate on the task of driving is a foremost priority for spirited vehicle handling.
However, the most often misunderstood effect of body roll upon vehicle handling is the effect of body roll upon camber-and the effect of camber changes upon tire traction.
Put simply, the larger the contact patch of the tire, the more traction exists against the road surface, holding all else constant. But when the vehicle begins to lean or roll to one side, the tires are also forced to lean or roll to one side.
This can be described as a camber change in which the outside tire experiences increased positive camber (rolls to the outside edge of the tire) and the inside tire experiences increased negative camber (rolls to the inside edge of the tire.) So a tire that originally enjoyed a complete and flat contact patch prior to body roll must operate on only the tire edge during body roll.
The resulting loss of traction can allow the tires to more easily give way to the forces of weight transfer to the outside edge of the vehicle. When this happens, the vehicle slides sideways-which is generally a bad thing.
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[murcielagoGTR]

How to Prevent Body Roll

By definition, body roll only occurs when one side of the suspension is compressed (moves into jounce), while the other extends (moves into rebound). Therefore, we can limit body roll by making it harder for the driver-side and passenger-side suspensions to move in opposite directions.
One fairly obvious method to achieve this is through the use of stiffer springs. After all, a stiffer spring will compress less than a softer spring when subjected to an equal amount of force. And less compression of the suspension on the outside edge will result in less body roll.
However, stiffer springs require the use of stronger dampers (struts or shock absorbers) and have an immediate and substantial effect on ride quality. So, even though handling is improved, they may not be the easiest or most cost-effective way to achieve the objective of reducing body roll.
For many enthusiasts, the use of anti-roll bars-also known as anti-sway bars, roll bars, stabilizer bars or sway bars-provides a more cost-effective reduction in body roll with minimal negative impacts upon ride quality.
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How an Anti-Roll Bar Works

Put simply, an anti-roll bar is a U-shaped metal bar that links both wheels on the same axle to the chassis. Essentially, the ends of the bar are connected to the suspension while the center of the bar is connected to the body of the car.
In order for body roll to occur, the suspension on the outside edge of the car must compress while the suspension on the inside edge simultaneously extends. However, since the anti-roll bar is attached to both wheels, such movement is only possible if the metal bar is allowed to twist. (One side of the bar must twist upward while the other twists downward.) So the bar's torsional stiffness-or resistance to twist-determines its ability to reduce body roll. Less twisting of the bar results in less movement into jounce and rebound by the opposite ends of the suspension-which results in less body roll.
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Factors that Determine Stiffness

There are two primary factors that determine an anti-roll bar's torsional stiffness: the diameter of the bar and the length of the bar's moment arm. Diameter is generally the easiest concept to grasp, as it is somewhat intuitive that a larger diameter bar would have greater torsional rigidity.
Torsional (or twisting) motion of the bar is actually governed by the equation: twist = (2 x torque x length)/(p x diam4 x material modulus.) And since the diameter is in the denominator, as diameter gets larger, the amount of twist gets smaller. Which, in a nutshell, means that torsional rigidity is a function of the diameter to the fourth power. This is why a very small increase in diameter makes a large increase in torsional rigidity.
For example, to compare the rigidity of a stock 15mm bar to an aftermarket, 16.5mm one, simply use the equation 16.54/154. Some quick math yields the figure of 1.46. In other words, a 16.5mm bar is 1.46 times as stiff-or 46 percent stiffer-than a 15mm bar of the same design.
Add just one more millimeter to the diameter of the bar-for a total of 17.5mm-and the torsional strength skyrockets to 85 percent stiffer than the stock 15mm bar (17.54/15.04 = 1.85).
However, in addition to the diameter of a bar, there is another very important factor that determines an anti-roll bar's torsional rigidity. This factor is known as the length of the moment arm-or in common terms, the amount of leverage between the vehicle and the bar.
As with anything, an increased amount of leverage makes it easier to do work. This is governed by the lever law: force x distance = torque. As distance-or the length of the lever-increases, the resulting amount of torque also increases. (This is why it was easier to move your big brother on the teeter-totter when he moved towards the middle and you stayed out on the end. You enjoyed increased leverage at the end, while he suffered from reduced leverage near the middle.)
Because an anti-roll bar is shaped as a "U," the ends of the bar that lead from the center of the bar to the end-link attachment serve as a lever. As the distance from the straight part of the bar to the attachment at the end link becomes longer, the torque applied against the bar increases-making it easier for a given amount of energy to twist the anti-roll bar. As this distance is reduced, torque is reduced-making it more difficult for a given amount of energy to twist the anti-roll bar.
It is this lever law that is applied during the design of an adjustable anti-roll bar. By using multiple end link locations, the distance from the point of attachment to the straight part of the bar can be altered. Or, in engineers' terms, the length of the moment arm can be increased or reduced in order to make more or less torque against the bar.
Using a setting farther from the center of the bar increases the length of the moment arm, resulting in more torque against the bar, allowing more twisting motion of the bar, creating more body roll. Using a setting closer to the center of the bar reduces the length of the moment arm, resulting in less torque against the bar, allowing less twisting motion of the bar, creating less body roll.
The actual impact upon torque can be compared by dividing the center-to-center distances of the end-link attachment points. For example, say the center-to-center distance of the stock rear anti-roll bar is 200mm. We can compare this to the 160mm distance of the firmest setting of a four-way adjustable 17.5mm bar by simply dividing the distances (160/200 = .8). In other words, a 160mm center-to-center bar produces only 80-percent of the torque that would be produced by a 200mm center-to-center bar of the same diameter. Or simpler yet, by using the 160mm end-link attachment points, we increase the stiffness of the anti-roll bar by an extra 20 percent.
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[murcielagoGTR]

What the Heck Is TLLTD?

TLLTD stands for Tire Lateral Load Transfer Distribution. While this term may sound complex, it simply measures the front-to-rear balance of how lateral load is transferred in a cornering maneuver. It is commonly used to compare the rate of lateral traction loss between the front and rear tires.
Put simply, there is only so much force that a tire can handle. When we ask more of the tire than the tire can deliver, it "saturates," or loses traction. If the front tires saturate before the rear tires, then we call this understeer or push-which means that the car tends to continue moving in the original direction, even though the wheels are turned.
If the rear tires saturate before the front tires, then we call this oversteer or loose-which means that the rear of the car tends to swing around faster than the front, causing a spin. When neither of these conditions prevail consistently, then we describe the chassis as balanced.
We can measure and compare the steady-state understeer and oversteer characteristics of a vehicle by assigning a lateral load transfer percentage of the front relative to the rear. A TLLTD value equal to 50 percent indicates that the chassis is balanced-or both the front and rear tires tend to lose traction at roughly the same time. A front TLLTD value greater than 50 percent indicates that the front tires lose traction more quickly than the rear tires-resulting in understeer. And a front TLLTD value lower than 50 percent indicates that the rear tires tend to lose traction more quickly than the front-resulting in oversteer.
It is important to note that our discussion of TLLTD only considers steady-state cornering maneuvers, such as a long 270-degree on-ramp or off-ramp. Moderate-to-aggressive throttle or brake application can upset this balance during a transient condition, briefly transitioning a vehicle from understeer to oversteer.
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[murcielagoGTR]

The Effect of Anti-Roll Bars Upon TLLTD

Ideally, you now understand how an anti-roll bar can be used to limit body roll, and you understand that reduced body roll can lead to a reduction in adverse camber changes for better tire traction. But what may not be obvious is the effect of anti-roll bar changes upon TLLTD (understeer and oversteer.)
In fact, given the above information, one might even assume that a firmer anti-roll bar, which leads to better camber control, would lead to better traction. If we add a firmer anti-roll bar to the front, traction loss diminishes, so understeer is reduced, right?
Wrong. Let's evaluate more closely the meaning of TLLTD-tire lateral load transfer distribution. Stated another way, we might describe TLLTD as the relative demand of side-to-side energy control that is placed upon the tires. Because a firmer anti-roll bar allows less deflection, it will transfer side-to-side energy (lateral loads) at a faster rate.
As the rate of lateral load transfer increases, additional demands are placed upon the tire. So if we install a firmer anti-roll bar in the front, then we increase the distribution of lateral load transfer toward the front tires. This increases the front TLLTD value, which will result in additional understeer, holding all else constant.
The same logic also holds true in the rear. A firmer anti-roll bar in the rear will increase the rate of lateral load transfer, placing more demand upon the rear tires, accelerating lateral traction loss and creating more oversteer, holding all else constant.
This is why blindly adding parts to your car may not produce the desired results. A wise consumer consults with-and buys from-knowledgeable experts that have the tools to make informed tuning recommendations.
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[murcielagoGTR]

I Want a 50 Percent TLLTD On My Car, Right?

Since on paper a 50-percent TLLTD indicates a balanced chassis, many enthusiasts are tempted to jump to the conclusion that this is therefore desirable. They may think that all cars should obviously come this way from the factory. Unfortunately, this is not the case-and the considerations are not that simple.
In reality, a car with a 50-percent TLLTD is literally on the constant brink of oversteer. And there are many factors that can quickly and easily take the car from the brink into a full-scale, out-of-control, spinning-in-circles disaster.
For starters, consider the effects of weather conditions that might create a wet or icy road surface. Or imagine that the driver happens to apply too much brake late into a turn-a common mistake among novice drivers. Or consider the effects of varying tire temperatures, tire pressures, or tire wear-all of which will have major impacts upon lateral traction thresholds. And of course, varying weight distribution, as a result of changing fuel tank levels, passengers, or the number of subwoofers in the trunk, will also impact TLLTD.
With all of these things to consider, automotive design engineers are forced to create a more conservative TLLTD. As a result, they intentionally target higher front TLLTD values so that stock vehicles will be prone to understeer-the assumption being that understeer is safer and more predictable for the average driver.
For example, a stock DOHC Saturn is tuned to produce a front TLLTD of approximately 63.4 percent-a relatively conservative target. (But give Saturn some credit, as this is on the aggressive end of the conservative spectrum, especially compared to other front-wheel-drive economy cars.)
As a general rule, an average street-driving enthusiast is probably willing to accept some compromises-within reason-of a more aggressive TLLTD in exchange for better handling. A suitable target is probably a front TLLTD value of approximately 58 percent, a value that is considered aggressive, but suitable for street driving.
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How do I Create the Right Handling Balance?

Since most enthusiasts do not have the knowledge or software needed to calculate chassis characteristics such as TLLTD, the responsibility falls upon knowledgeable tuners.
Obviously, TLLTD and body roll will both be affected by changes to springs and anti-roll bars. While understanding the effects of multiple changes can get confusing, the answer is usually only a phone call away.
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Brake tech

Increasing your braking performance is one of the easiest-and cheapest-ways to lower lap times. By shortening your braking distances, you can stay on the power longer and drive deeper into the corners. This may sound academic, but too many racers take brakes for granted and thus neglect one of the most important aspects of their car's performance. On the track, as well as on the street, good brakes can also be the difference between life and death.

One of the easiest ways to increase your braking potential is to select the right compounds for your brake pads and shoes. Spending lots of time and money retrofitting trick, aftermarket big brakes could be a waste if you haven't first maximized your current brake setup.

Proper pad and shoe selection can make the difference between being a back marker and being a contender. Carbotech Engineering's Larry Narcus-a chemist with 30 years experience in plastics who has since decided to devote his energies to manufacturing better brake pads and shoes-tells of a customer with an Improved Touring Corvair came to him looking for some shoes. Now, if you're familiar with Corvairs, then you know that they have big drum brakes at all four corners. Not exactly high-tech, but according to Larry, they can be made to stop well with the proper shoe selection. Next time out, with the proper shoes in place, the Corvair driver dropped six seconds off his lap times. Think about that: six seconds. How much would you pay to drop that much from your lap times?

Not All Compounds are Created Equal
What's the secret to choosing the right pad or shoe? Obtaining a basic understanding of your needs and then matching them to the proper compounds. It's also useful to listen to the experts (hopefully, the people selling the stuff).

Brake pads and shoes, like a lot of things in this world, are available in a large number of flavors. Some are good, and others are so-so. Understanding this will make life easier. Let's take a look at what kinds of compounds are available:
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[murcielagoGTR]

Organic: These are the $6.99 pads that you can get at the local parts shop; essentially, you get what you pay for. Organic pads are made up of compressed wood and/or paper, and perhaps some low-grade metal has been thrown in. Their friction coefficient (how well they grip against the rotor or drum surface) is very low, and they can't handle the high temperatures associated with any sort of performance driving. Basically, these pads not appropriate for competition use.
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· Semi-metallic: These are definitely a step in the right direction. Expect to find much more metal in the mix (probably iron, but maybe brass or bronze) along with a better binder (what holds the pad together). The friction coefficient is higher (meaning the pads will provide more bite against the rotor) and they will wear better. Semi-metallic pads and shoes are the basic $30/pair-type found down the street. Usually a better choice over organic compounds, but you could do better.
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· Carbon-based metallic: This is the good stuff that we'll be talking about today. The price goes up a bit, but performance rises many times over. Carbon and various metals (iron, nickel, brass and bronze) are thrown into the mix, and a better high-temperature epoxy binder holds everything together. The friction coefficient is much higher than semi-metallic pads, and in general they are also less dusty. Carbon-based metallic pads are offered by several companies in many different compound mixes. Hawk, Performance Friction, Porterfield, Cool Carbon and Wilwood (Polymatrix) all offer quality carbon-based metallic pads. Besides selling brake pads, Carbotech and TS Imported can also reline the backing plates from drum brakes with these modern materials.
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· Carbon-carbon: Odds are you don't have these brakes (carbon-fiber rotors with carbon-fiber pads), unless you run in FIA races in Europe.
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Choosing a Compound

Even carbon-based metallic pads are available in different compounds; choosing the right one may require some research and soul-searching. Basically, you need to match the right pad to your application. If you're worried that no one has pads or shoes for your oddball application, rest assured that some suppliers can do custom installations or reline your existing backing plates.

But how do you know which pad is right for you? Well, since no pad can do it all, you need to look at several different areas of concern when shopping for brake pads and shoes. By discussing these concerns with the different suppliers, you should be able to match your needs to the right product.

· Your first concern should be stopping power. This is measured by a friction coefficient, and the higher the coefficient, the more stopping power available from that compound. However, compounds with very high friction coefficients tend to be hard on rotors and drums, which may not be desirable in some situations (like on the street or in an endurance race). Like most things in life (brake pads included), it's a trade-off where you must look at the whole picture and decide which concerns are most important for you and your application.

· Modulation, the lack of the tendency for the brakes to lock up, is also a high concern for most of us. Modulation helps control the car, as locking up the brakes can put you in a spin. Again, different racers need different degrees of modulation. An autocrosser, to whom every hundredth of a second is valuable, simply cannot afford any lockup. Therefore, lots of modulation is important to him. An endurance racer, on the other hand, can deal with less modulation if it means getting longer pad life.

· Fade resistance is another big factor. Every compound has a temperature range in which it likes to operate; matching the compound to your brake temperature range is crucial. Most racing pads have a 600 to 800 degree window for their operating temperature, while brake temperatures generated by street driving tend to be much lower. So there is no way a great road race pad designed to work under high temperatures is going to stop well on the street. Nevertheless, many people seem to labor under a major misconception as they buy "racing" brake pads for their street cars and, when these pads fail to meet their expectations, they feel cheated. Be honest with yourself and buy wisely.

Likewise, a heavier car is going to generate more heat than a lighter car. By working with your vendor, you should be able to match your driving conditions to the proper compound. Tell them what conditions you race under, what tracks you visit and how hard you are on the brakes.

· Rotor and drum friendliness can also be a factor to some drivers, especially those with older cars. Some compounds, while they'll stop you on a dime, can be very hard on rotor and drum surfaces. If you race a car for which these replacement parts are hard to find, like a vintage Bugatti for example, then having friendly pads and shoes may be a prime concern-perhaps even more important than absolute stopping power. Likewise, a set of pads that will chew up a set of rotors every three hours will be of little use to a racer about to run a four-hour enduro.

· For a lot of us, economics also need to be addressed. However, don't simply look at the final price when shopping for new pads and shoes. If a pair of brake pads costs twice as much as the competition but lasts three times as long, which is the better deal?

· While not a huge concern for everybody, brake dust and squeal can be a factor for some people. If neglected, dust can attack the finish on a set of wheels, quickly turning a prized set of rims into an eyesore. At the extreme end, hot flakes from the brake pads can land on the fenders of a car, singing the paint. Now, a road racer may be willing to pay that price, whereas a street driver may not.

For a lot of people who only drive on the street, squealing brakes can be a major inconvenience. If you don't like being tortured by a set of wailing brake pads, move this consideration to near the top of your list.

· The rate of wear is also something to think about, although it is related to many of the factors we already discussed. But to bring back our endurance driver, it may be the most important factor when selecting new shoes and pads. Again, be sure to discuss this factor with the guys selling the goods.

Speaking of wear, some companies offer slightly thicker pads designed for endurance racing. As a side benefit, these thicker pads seem to handle heat better and provide better braking characteristics. (The more pad material, the bigger the heat sink). While extra-thick pads may seem like the answer to everyone's problems, there is a limit-make the pads too thick, and you'll need thinner rotors, which is not a good move.

 

[murcielagoGTR]

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Matching the Pad to Your Application
The biggest part of buying brake pads is matching the compound to your application. So, let's take a look at some common applications and what kind of braking compound characteristics they require.

· Though they may seem different at first, autocrossers can require the same compounds as high-performance street drivers. Both need effective cold stopping power and lots of modulation.

In autocross, there is no time to bring the brakes up to the temperatures required by many "racing" brake pads. You need full stopping power right off the line, and you need it right away. Likewise, when out on the street, you also have no time to wait for brakes to heat up, and here the stakes are a lot higher. On the street, your brakes have a lot of time to cool off between stops, so it is important to pick a pad that will be happy to work while cool. For both applications, look for compounds designed to work in the 100- to 800-degree range.

Modulation is also important, both when autocrossing and on the street. It's the kiss of death for an autocrosser to lock up a brake. A skid means lost time, which means the run is junk. With only three or four runs at an event, that can be the end of any chances of a trophy. On a road course, a racer can usually overcome or bounce back from a skid on the same lap; autocrossers, by the nature of their sport, don't have that luxury.

Cost and a lack of audible squeal can also be factors, depending upon the individual. Some of us are also willing to live with more dust than others.
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· Track events and drivers schools are gaining popularity; these drivers also need to select the right compounds for their needs. Generally, they will be looking for good modulation and lots of stopping power. The main difference between them and the autocrosser is the temperature range of their brakes. Generally, and depending upon the car, driver and track, they'll need to select a compound that works in the 300- to 1100-degree range.

These pads and shoes require some heat to work properly, so you should strongly consider swapping to these "track pads" before heading out on course-just as you mount sticky tires before an event.
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· Road racers, whether they be sedan or formula car drivers, also have to look at more at fade resistance. Stopping power and modulation is still very important, but fade resistance throws a new factor into the equation. This will require a pad that can work in the 400- to 1400-degree range, depending on track, car type, length of event, level of brake cooling and driving style.

As road racing conditions can change from event to event, you may want to consider using different pads for varying conditions. Remember that a track like Sebring is a lot harder on brakes than Roebling Road.

Weather conditions can also cause a change in braking compound requirements. In the rain, you may need more modulation than all-out stopping power. Racers are eager to change tires when faced with rain, but why not brake pads? In some situations, like at last year's rainy ARRC, rain and its effect on stopping power is a deciding factor for many drivers.

Economics and rotor/drum friendliness can also be factors for road racers, especially those running endurance events or driving older cars for which replacement brake parts are getting harder to find. As we discussed before, rotor and drum friendliness may be top priority for a vintage car racer.

So, which brake pad is best for you? Unfortunately, there is no way we can tell you exactly which pad or shoe will work best for your application. Hopefully we have educated you enough so that you and your retailer of choice can intelligently discuss your needs and match you up with the proper compound. Doing so may take some testing and time, but in the end you'll have the stopping power you need.
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Brake Fluid

While you're focusing on brake pads, don't forget to check out your brake fluid. If you can't remember the last time you changed your brake fluid, do so now. Brake fluid absorbs moisture over time, which causes a large number of problems, including spongy brake feel, rusting components, etc.-none of which you really want to deal with. Speaking of brake fluid, remember to bleed it often at an event, especially if you're racing in a humid climate. Your brake fluid is expected to work under some incredibly hot situations. In many cases, this is also a weak spot in the system.

When buying fluid, remember that the higher the rating, the better the stuff. DOT 4 fluid is better than DOT 3, and DOT 5 is better than DOT 4. However, beware of silicone-based DOT 5 fluid-it can give you a mushy pedal. Go with glycol-based DOT 5.1.
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[murcielagoGTR]

Brake Lines

When you stomp on your brake pedal, the fluid not only pushes through the brake lines, it also pushes against the brake lines, causing inefficiency in the system. How can you combat this loss? Replace the stock rubber brake hoses with braided stainless-steel lines. The swap is fairly easy and inexpensive. Expect a firmer pedal when done. Check your rulebook before making this mod; also, not all stainless lines are DOT-legal.
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Brake Ducts

Brakes work on the simple principle of converting kinetic energy into heat energy; helping your brakes get rid of that heat will allow them to function more efficiently. Hence, a little duct work may be in order. Scoops and duct materials are available from numerous race shops. Likewise, running wheels that have a lot of space between the spokes will also help disperse heat.
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Master Cylinder

Is your master cylinder junk? Then either replace or rebuild it right away. As the heart of the braking system, a master cylinder's health is vital to proper braking. If it's time to replace your master cylinder, remember that bigger is not better; moving to a master cylinder with a larger cylinder diameter will result in lower line pressure, causing less pressure between the pad and the braking surface. This is bad.
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Bias Knobs

Have you severely lowered your car? Doing so can mess with the front-to-rear brake bias, which now needs to be changed. A brake bias knob, located inside the cockpit, allows the driver to adjust the brake bias as needed.
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Pedal Covers

It may seem obvious, but having slippery brake pedal covers can hamper braking. Ever step on the brakes and have your foot slip off the pedal? Whether you install some fresh, new, original-equipment rubber pedal covers or trick, drilled-out pieces, you'll be in better shape.
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Practical Test

All of this talk of brake pads is great, but we needed a little practical exercise to back it up. We wanted to measure how much a swap in brake pads alone would change things in the real world.

For the test vehicle, we grabbed our editor's 1988 Honda CRX Si. Several factors made his CRX a prime candidate: First, with almost 170,000 miles on the clock, this car's brakes were nothing to write home about. The system had been well maintained during that time, but the brakes were average, at best. The fluid was fresh, but the system lacked any real bite.

We also wanted to see how well a disc/drum system could work with the proper compounds. A lot of people consider drums yesterday's news, but we wanted to see if a set of modern compounds would make them happy.

Finally, big-brake swaps on Hondas are all the rage. Everyone and their brother is touting cross-drilled, slotted and over-sized rotors for the front and rear of Hondas. We wondered if could we get killer performance for a fraction of the cost and without the hassles of re-engineering our brake system.
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Baseline Tests

Before performing any baseline tests, we refilled the brake system with Castrol LMA brake fluid, bled the brakes and checked our tire pressures. Except for the Personal steering wheel and AutoThority short-shift kit, the rest of the car was bone stock.

We grabbed our Vericom VC2000PC on-board data acquisition system, put J.G. (our resident hot-shoe driver) in the driver's seat, and set out for our top-secret test site.

Then we did some baseline tests. Our first stop from 60 mph took only 148 feet while generating .875g of force. The stop took 3.62 seconds, and some right-rear lockup was observed.

By our second stop, the pads were already showing they were giving up the fight-it took an additional 10 feet to stop from 60 mph. Our g force readings had fallen to .840 g, and the stop took 3.83 seconds.

Things didn't get any better after that. Our CRX took 161 feet to come to a halt by the fourth run. Fade was running rampant, and it was already time to allow the brakes to cool off. We ran some more stops that day, and our g force readings hovered in the .84 to .88 range. The average was .858g over the eight stops we measured. Before heading home, we had to drive around a bit so the brakes could cool.
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[murcielagoGTR]

Looking to Improve

With our baseline figures in hand, we started our search for new pads and shoes. This is a street car, remember, so cold stopping power is very important. We also plan on autocrossing the car, so fade and modulation were also high on our list.

Larry Narcus at Carbotech listened to our requirements and matched us up with the goods. Up front we would try his new "Mean Green" Kelated-metallic pads. These are designed to work in the 100- to 750-degree environment, perfect for the street and autocross use. He also promised no fade and excellent modulation. For the rears, we would try his Silver Streak shoes. These offer a slightly lower friction coefficient than the Mean Greens and would compliment the Kelated-metallic front pads, he said.

Randy Duval at AllSpeed helped install the new pads and shoes, which were no harder to install than your garden variety OE pieces. We found our original-equipment pieces to be rather worn, probably not entirely unlike most street cars out there. Our rotors were looking a bit thin, but we decided to keep them on and see what the pads alone would do.

With the Carbotech pieces installed, we followed Larry's instructions and properly bedded in the pads. Then it was time for more testing.

J.G.'s first run on the Carbotechs registered an astonishing .929 g. However, the stop took 162 feet. This was probably due to the fact that the pads were still unfamiliar with the irregular surface of the rotors. Also, our CRX had average street tires on it, but like we said, we wanted to simulate a real-world test.

The next stop saw the distance plummet to 144 feet at .896g. The stop took 3.40 seconds and J.G. reported that modulation was excellent.

We ran seven more stops that session; by the end we had the stopping distances down to 141 feet. Even towards the end of the test, the brakes were still stopping well, showing g force readings as high as .995g after half a dozen repeated stops from 60 mph. We averaged .923g over the nine stops we recorded with the Carbotech shoes and pads. Our stops took as little as 3.18 seconds and the stopping distances were now as short as 140 feet.

At no time during this test did we observe fade or any modulation problems. Unlike the stock pieces, we never had to allow the brakes to cool off once we installed the new shoes and pads.

These tests were all conducted literally minutes after the Carbotech shoes and pads were installed, so naturally the braking performance should only get better as the pads conform to the rotor surfaces. We have gone ahead and ordered some new rotors; we can't wait to see how the pads work against a fresh surface (we'll have the pads resurfaced before installing them). As for tires, we'll test the car again once some fresh rubber arrives. Remember an important fact: the brakes stop the wheel; the tires stop the car. Your brakes are only as good as your weakest link in the system, and right now our tires can't keep up with our brakes. And yes, all of this data will appear in a future issue.

This simple brake pad and shoe change has given us fantastic brakes for a fraction of the cost of a over-sized, drilled rotor conversion. It may not look sexy, but it certainly gets the job done.

Any down side to these pads? Not really, although we have gotten some squeal under low line pressure situations (like when slowly rolling to a stop). There is also some dust, but that's why wheel cleaners were invented. Still, for day-to-day driving, we have to say that these brakes are perfect.
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[murcielagoGTR]

Trusims:

In the world of braking, there some facts that are undeniable.
· A brake pad or shoe that isn't wearing isn't working. Remember, the things have to wear to work.
· You're going to get what you pay for. (Where isn't this true?)
· There's a brake compound out there for everybody; you just have to do some looking to find it.
· No one really knows what causes brake squeal. All brakes produce squeal, but our ears cannot always hear it.
· The rear brakes are there for a reason. Just because the fronts do most of the work, don't neglect the rear brakes.
· Brake pads and shoes are only part of the story; make sure your entire braking system is up to snuff.
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