SYMPTOM: Uneven Pad Wear

CHECK THE FOLLOWING:

It is very important to understand the manufacturer's recommendations in regards to bedding in your new brake pads and rotors. The following guidelines will help assure you that the correct steps are being taken. Some brake pad companies, offer pads that are designed with a unique processing stage called burnishing. Burnishing simulates the first few minutes of a pad on the racecar by applying heat and pressure to the pad while in the final stages of production. This process is a great advantage to you because the break in or bedding procedure normally needed with other types of brake pads has already been started before you install the pads. This eliminates the cost normally associated with bedding in brake pads because you will not need to use your motor, tires, and fuel to prepare your brake pads for racing. It is important to build heat in the pad prior to racing. This step can be done simply by dragging the brake while entering the track or by making two or three hard stops just before taking the green flag. Remember most brake pads operate best at higher temperatures, so it is best to heat them up before each race by following the above steps. Non-burnished racing brake pads will require a bedding in procedure that will differ slightly between manufacturers. The following is a guide that covers most manufacturers' recommendations (it is best to contact the manufacturer for exact instructions). 1. Slowly build heat in the pad by making slow stops, being sure to allow a minute or two for the pad to cool down while the car continues to move. 2. Repeat above step two or three times. 3. At full speed make hard racing type stops again, allowing cool down time between stops. 4. Repeat above steps two or three times or until brake fade is noticed. 5. Allow brake system to completely cool. Your pads should now be race ready. (It is important to remember that the pad and rotor surface must be mated to each other before ultimate performance will occur.)

BRAKE ROTOR BREAK IN PROCEDURE

Again it is very important to know and understand the manufacturer's recommendation for this step. The following is a guide that covers most manufacturers' recommendations: new rotors should be heated up very slowly and, if possible, use a set of pads that have already been exposed to racing use. For best results, break in the rotor with the same type of brake pad (compound) that you intend to use with the rotor. This will help assure that different friction materials will not build up on the rotor. After the above step has been completed, inspect the rotor-rubbing surface. A uniform polished appearance with no cracks or grooves is what you should find.

BRAKE FLUID

Many brake system problems are caused by old or inadequate brake fluid. It is very important to always use a high quality fluid with a high dry boiling point rating. There are also many theories as to what type of fluid should be used. The following information should help you better understand the differences regarding different types of fluids. A. Silicon based fluids: most all silicon-based fluids are very easy to compress. When using a fluid that is easier to compress it must be noted that a spongy pedal will likely be noticed. Many times the pedal will continually get even spongier as the fluid gets hotter. Another characteristic about silicone fluid, is its inability to mix with water. When the water begins to boil, it can cause the system to air lock. It should also be noted that silicon based fluid is not recommended in AFCO type master cylinders. B. Glycol based fluids: theses types of fluids are the most widely used and maybe the least understood. It is very important to understand that this fluid will mix with water. It is also important to remember that the boiling point of the fluid will drop considerably as the fluid mixes with the moisture in your brake system, making it extremely important to completely purge the entire system very often. No matter the type of fluid you choose, it is a good idea to change it often and never use fluid from an open container because of the potential for moisture.

BLEEDING THE BRAKE SYSTEM

To assure yourself of a properly bled system, the following guidelines should be followed: always use new fluid. (DO NOT REUSE NEW fluid.) Always use a clear hose and container so you can view the fluid as it exits the system. Always begin bleeding with the furthest caliper from the master cylinder. Always push the pedal slowly all the way down and allow pedal to remain up momentarily to refill master cylinder bore. DO NOT jab the pedal. Only open bleeders the amount needed to spray fluid out. Opening bleeders too far can cause air bubbles to form. While pressure bleeding is much easier than manual bleeding, it is important to manually bleed the system every so often. This allows a check of fluid flow that would not normally be seen while using the pressure bleeding method.

MASTER CYLINDERS

It is important to match the proper size master cylinder with the vehicle's weight, type of racing, and driving style. Several important points to remember are as follows: the smaller master cylinder bore will create higher pressure in the system. The larger master cylinder bore will create more volume in the system, and will tend to give the pedal a firmer feel and less pedal travel.

BRAKE CALIPERS

Caliper selection is a very important part of a correctly operating brake system. The type of racing, weight, car, surface, and driving style are all elements that should be considered when choosing a selection of calipers. Besides the overall size and style of the caliper, it is important to know what size caliper pistons will be best for your application. Larger pistons will create more pressure on the brake pad backing plate. The opposite is true with small caliper pistons. Some calipers are designed with multi size pistons to aid in proper proportioning of brake pressure and help assure less pad taper.

DUCTING AIR TO BRAKE SYSTEM

Heat created by brake system components can sometimes cause problems that are hard to diagnose. Many times racers blame the problem on brake pad fade. Fade is almost always caused by heat. In most cases, removing the heat from the rotor and caliper area can rid the system of fade. The important thing to remember, and what is very misunderstood is ducting should be used to force hot air away form the hot component, not blow cool air on it. By removing the heat, the component will operate cooler. For best results, force cooler air across the components making sure that the air that is being removed has a path to follow that will not allow the heat to build up someplace else. Duct size should be as big as the application will allow, and directed in the shortest and straightest route possible. It may be helpful to experiment with duct locations. On dirt cars try to install the duct in areas that don't see an excessive amount of dirt or mud, and install a fine mesh screen in the duct hose to help trap air borne dirt. On asphalt and road racecars, try to install duct on flat areas, avoiding areas that allow air to pass over the duct inlet. If the application allows, use one duct hose directed to the center of the rotor, and another directed to the caliper area, preferably directed down toward the top of the caliper; this will force hot air from the pad area. Many types of ducts are available with many applications. Be certain to match the correct duct with you application.

ROTOR AND BRAKE PAD TEMPERATURE

Before choosing a brake pad (compound), it is very helpful to know what temperature your system operates at. System temperature will change depending on the size of track and driving style. It is very important to factor in the change to assure your system works correctly. Most racing pads work best at certain temperatures. Running a pad that works best at very high temperatures will not give the best results if the temperature is lower than the specified range. The same is true when using a low temperature pad in a high temperature situation. Many problems can be avoided by using heat sensitive paint on rotors, pads, and calipers. This type of paint burns off when the specific temperature is reached; allowing you to pinpoint how hot the component is getting during race conditions. Tire pyrometers can not accurately tell you what temperature the components are because of the cool down time involved.

OVERALL BRAKE SYSTEM MAINTENANCE

Proper brake system maintenance is essential to assure the best performance and long life of your system. Always use a checklist in regards to weekly maintenance. Sometimes overlooked items that should be checked for include checking for misaligned caliper brackets and loose caliper bolts. Inspect all lines and fittings for even the smallest leak. Reposition and monitor air ducting placement. It is also a very good idea to remove the pistons from the calipers and inspect them for abnormal wear. Never replace used caliper O-rings after removing them from the caliper. rotors and pads should be checked for extensive cracking and wear rate. Always examine the tabs or ears on the rotor, looking for any signs of warping, cracking, or any other unusual signs of wear.

RECOMMENDED BRAKE TIPS

Always use fresh high temperature fluid. Completely drain and purge system often.

• Follow a checklist regarding brake system maintenance.

• Never hold hot brakes on for long periods while not moving.

• Know your operating temps, and monitor temperature when changing components.

• Replace caliper O-rings often.

• Use hard brake line wherever possible.

• Use safety wire to secure rotor and caliper bolts.

• Mount calipers with bleed screws up.

• Only use residual pressure valves as a last effort.

• Try to maintain between 800 and 1200 psi in your system. (Never exceed 1500.)

• Bleed dual master cylinders separately by disconnecting push rod from balance bar on first master cylinder, and then repeat on the second.

• For best results, use the same rotor and pad compound combination to help guard against glazing of pad or rotor surface.

• When changing pad compounds, bead blast rotor friction surface to remove old pad material buildup.

This article explains the workings of the 4-link suspension and the tuning methods used to maximize its performance under various track conditions. This information applies only to 4-link rear suspensions having links floated on the rear axle (via birdcages) with all links running forward.

The 4-Link Difference Upper Links Lower Links Indexing AFCO Springrod AFCO Clamp Brackets

The popularity of the 4-link suspension is due primarily to its ability to let the race car turn freely in the middle of the corner without compromising forward bite. To understand how a 4-link can be made to provide such handling, you must first understand a few basics about rear suspensions.

Realize that you can increase forward bite on any type of rear suspension by angling the trailing arms upward toward the front of the race car. Trailing arms mounted in this manner cause the rear tires to try to drive underneath the chassis as the rear axle pushes the race car forward (See illustration 1). As a result, the loading of the rear tires (during acceleration) is quickened and forward bite is enhanced.

Illustration 1.

There can be a handling trade-off, however, to the forward traction gained by running the trailing arms upward to the front of the race car. During chassis roll, trailing arm/s mounted upwards will cause the right rear tire to move rearward (until the arm/s reach a level position) and the left rear tire to move forward. The condition is referred to as "loose roll steer". (See illustration 2A.)

Generally, bottom link angles from 0º to 5º downhill (to the front) are used to help control loose steer. Some forward bite may be lost when the bottom links are lowered but the effect on forward bite is usually minor relative to the overall handling improvement that is realized by reducing loose roll steer.

Another method used to reduce the loose roll steer of a 4-link suspension is to shorten the bottom links. Notice, in illustration 2D, how the shortened bottom link pulls the bottom of the right side birdcage forward during chassis roll more than the longer links in the other illustrations. The bottom of the left side birdcage does lose some of its rearward movement because of the shortened bottom link. But since left side birdcages typically move down much less than right side birdcages move up during chassis roll, the overall effect, when shortening the lower links, is a reduction in loose roll steer. However, if the left rear of your chassis hikes up during cornering, loose roll steer may increase whenever both bottom links are shortened!

We could reduce loose roll steer even further by combining the long bottom link arrangement of illustration 2C on the left side and the short bottom link arrangement of illustration 2D on the right side. The preceding paragraphs should help you understand why.

The length of the bottom links are dependent on the roll steer and traction characteristics desired by the chassis tuner. For most track conditions, bottom links 2æ shorter than the upper links work well. Short links( from 3æ to 4æ shorter than the upper links) generally work best for tight, flat race tracks or on any track where the chassis tends to be loose. Long bottom links (equal in length or no more than 1æ shorter than the upper links) work best for fast tracks or on any track where the chassis tends to push. You should use the information in this article to determine the correct link lengths for your application.

However, a proven 4-link arrangement includes 15 1/2æ bottom links, mounted 5º downwards to the front, coupled with 17 1/2æ top links, mounted 15º upwards to the front.

Even though it is the oldest type of automotive suspension, leaf springs continue to be a popular suspension choice among racers. Though simple in appearance, a leaf spring suspension involves many intricacies understood by few racers. The following information should help you to better understand and consequently, better tune a leaf spring suspension. The information applies only to unsymmetrical leaf springs with shackles mounted above the leafs (typical of most race cars), unless noted differently.





When a leaf spring is checked for rate, its ends are first attached to rollers. A leaf spring produces fairly consistent rates when checked in this manner. However, a leaf spring can produce an installed rate stiffer or softer than the checking mechanism readings. It is important to understand the installation factors that affect a leaf spring's rate.

For instance, the axle mount deadens part of the leaf and an increase in spring rate results. The increase is proportional to the amount of spring that is deadened by the mount. You can expect an increase in spring rate after replacing "factory type" rubber lined axle mounts (which deaden relatively little of the leaf) with solid axle mounts and lower plates.

Any lengthwise twisting of a leaf spring will also cause an increase in spring rate. The increase is proportional to the degree of the twist. The twist results from stagger, wedge, bent axle tubes, misaligned chassis mounts, etc. that cause the axle mount and spring to be at an angle to each other from a rear view.( see illus. 1) The leaf twists whenever it is tightened flat to the unparallel axle mount.

Illustration 1.

You can eliminate any static leaf spring twist by shimming or angle milling the axle mount or lowering block, or by angling the leaf and shackle frame mounts. However, twist will still develop as soon as the chassis begins to roll!

Leaf twist is more pronounced with solid type leaf eye bushings than with the more pliable rubber bushings. Practically all potential for twisting a leaf spring is eliminated by using an AFCO front eye pivot instead of a bushing.

Your leaf will become softer as twist in the leaf is reduced. At the least, you should eliminate any static twist present in your leaf springs whenever your chassis is at ride height. Otherwise, you may unknowingly change rear spring rate whenever you replace or adjust rear suspension components.

A static tension in the leafs is present whenever the leafs and axle mounts are not parallel from a side view(see illus. 2). Any static tension will cause an increase in spring rate. You can check for this tension by placing jack stands under both leaf springs directly below the axle and then unbolting one side of the axle from its leaf (use this same procedure on both leafs to check for lengthwise twist). The axle mount should seat evenly to the leaf as viewed from the side. If necessary, reposition the axle clamp on the axle tube to eliminate any twist. AFCO clamp-on axle brackets will facilitate corrections.

Illustration 2.





 

Illustration 3.

A good starting point for shackle angle is 90 degrees. In this position the shackle has no effect on spring rate. Keep in mind that the shackle angle changes (and consequently the spring's effective rate changes) whenever the suspension moves. Also, the shackle's angle will change whenever you change the chassis' ride height, the arch of the leaf, the load on the leaf, or the length of the shackle. Since the shackle direction changes when the leaf is deflected past a flat condition, you should avoid deflecting the right rear leaf to an extremely negative arch condition. This could cause a very large shackle angle at high loads and consequently a very soft spring rate. Excessive body roll and poor handling could result. You can correct this problem by decreasing the shackle angle, increasing the arch, of the spring by increasing the rate of the right rear leaf spring.

Shackle length is another factor affecting the rate of a leaf spring. A short shackle will change its angle (and the effective rate of the leaf spring) quicker than a long shackle upon deflection of the leaf. There is a second shackle effect on the stiffness of the rear suspension that counteracts and sometimes exceeds the shackleºs effect on spring rate. This second effect occurs whenever the shackle swings in its arc and moves the rear spring eye vertically.(see illus. 4)

Illustration 4.

The vertical movement of the rear spring eye causes a jacking effect. If the shackle movement forces the rear spring eye downward, the leaf will deflect and exert an upward force on the chassis that will add stiffness to the rear suspension. Conversely, the shackle will reduce suspension stiffness if t causes the rear spring eye to move upward during suspension travel.

The stiffening effect occurs during suspension deflection whenever the rear spring eye is ahead of the upper shackle pivot and the shackle is moving rearward (see illus. 4, example B). In this position, however, the shackle also produces a softening effect by reducing the effective rate of the leaf spring (due to the large shackle angle). The overall effect to the stiffness of the rear suspension is determined by the greater of the two shackle effects. Under opposite conditions, you can expect a reversal to the above effects. If the rear spring eye is located behind the shackle pivot (illus. 4 example A) the shackle effect will tend to reduce suspension stiffness whenever the shackle moves rearward. However, the small shackle angle will tend to stiffen the spring's rate. The overall effect to the suspension's stiffness is determined by the more dominant of the two shackle effects. Keep in mind that the movement of the rear spring eye (from its static position) is mostly forward under racing conditions.

If a leaf goes into negative arch the travel direction of the shackle changes and the shackle effects change. Handling is not consistent under these conditions.

The second effect of the shackle can be enhanced by increasing the length of the shackle. Generally, the second shackle effect (jacking)is dominant.

Illustration 5.

A. More Arch:
•	Raises chassis
•	Raises roll center (causes less chassis roll and less rear side bite)
•	Increases wedge when arch is increased on LR only (makes chassis tighter off corner)
•	Changes roll steer (may help car to turn)
•	Increases shackle angle (may cause a
	change in spring rate�see shackle section)
•	Decreases lateral stiffness of the rear suspension (may improve side bite but could make the chassis feel loose)

B. You can expect handling changes opposite to the above when using leafs with less arch.

1. More "tight" roll steer (may tighten handling) 2. Increased rear suspension stiffness 3. Lowered roll center(increases body roll and rear side bite-handling tightens) 4. Less body/tire separation during acceleration and deceleration (may tighten initial corner entry handling and may reduce initial forward bite)

You can expect results opposite to the above when you raise the front eye of the leaf and adjust the chassis back to its original ride height. Mounting the leafs so that the front eyes are slightly inboard of the rear eyes will cause the leafs to have more lateral stiffness. This can make the chassis feel tighter and may help prevent the rear suspension from binding due to excessive lateral deflection of the leaf. However, if the leafs are offset too much, the suspension becomes too stiff laterally and rear side bite is lost. Whenever the body slides� over the rear end during cornering, the splayed leafs can cause rear steer that will help the car to turn. Also, if the right front spring eye is mounted more inboard than the left eye (measured from the corresponding tires), the right rear tire will tend to be loaded less than the left rear tire during acceleration. As a result, the chassis will tend to be tighter off the corner. Corner exit handling tends to be loose under opposite conditions Generally, moving the front spring eye 1 1/2" laterally will produce a noticeable effect to corner exit handling.

Too much lowering block* can cause the forward thrust of the rear axle to prevent the leafs (or torque arm) from wrapping up and absorbing engine torque. Consequently, forward bite is diminished. A symptom of this problem shows up on torque arm equipped cars as very little 5th coil/shock movement.

*The distance between the bottom of the axle tube and the top of the leaf should not exceed 4 1/2". What to look for in a quality leaf spring: 1. Smooth, continuous and consistent arch 2. No lengthwise twist 3. High strength steel 4. Heat treated 5. Tension side of leaf shot-peened for increased durability (produces a satin smooth finish) 6. Rubbing blocks between secondary leafs 7. Secondary leafs taper cut at ends. 8. Proper eye alignment (front and rear eyes should be parallel in all directions).

Remember, the many factors of a leaf spring suspension are interrelated and a change to one aspect of the suspension usually affects others. Consequently, the handling results are not always as predicted! Hopefully this text will provide you with the understanding necessary to correctly analyze handling and adjust your leaf spring suspension correctly.

What is Spring Rate?

Spring rate refers to the amount of weight needed to compress a spring an inch (Example:500# per inch) To understand and properly check a spring for rate you need to know the factors that determine the rate of the spring. Fortunately, there are only three things that affect spring rate, so there's not that much to remember!

1.	Wire diameter. This affects rate since greater diameter wire is stronger than lesser diameter wire. So, when wire diameter is increased, spring rate increases.
2.	Mean diameter of spring. Mean diameter is the overall outside diameter of the spring less one wire diameter. When mean diameter increases, the spring rate decreases.
3.	Active coils. Determination of the number of active coils varies according to spring design. Count the total coils minus two for springs with both ends closed (includes all AFCOILS). Count the total coils minus one for springs with one end closed and one end open. As the number of active coils increases, the spring rate decreases.

 

If a spring's rate is linear (most racing springs have linear rates) its rate is not affected by the load put onto the spring. For example, a linear rate spring rated at 500#/inch will compress 1" when a 500# weight is placed onto the spring. If another 500 pound weight is put onto the spring the spring will compress another inch. At this point the load on the spring has increased to 1000 pounds. The rate of the spring, however, remains constant at 500#/inch.

If the load put onto a spring increases the rate of the spring, the spring is said to have a progressive rate. Progressive rate springs are sometimes used on torque arms to absorb engine torque. Keep in mind that the load (or preload) put onto a progressive rate spring can greatly increase the rate of the spring.

Typically, progressive rate springs are made by varying the spacing between the springs' active coils. During compression the close coils bottom out and deaden. This reduces the amount of active coils and spring rate increases as a result.

Springs that are designed to include coils of different diameter or are wound using a tapered wire will also produce a progressive rate.

Most coil springs are actually progressive to some degree -- as we will learn later!

Dynamics of Coil Springs:

There are basically three different spring designs presently used in race cars. They are:

The 3 springs types are used in different situations and provide different effects to rate. Since the designs are so varied, it only follows that the dynamics of each design are also varied (more later). You must remember, however, the only factors that affect spring rate are wire diameter, mean diameter, number of active coils.

How Spring Rates Change Dynamically:

Keep in mind that as a coil spring compresses, the inactive (dead) end coils gradually contact adjacent, active coils. The contact causes the active coils to deaden which increases the rate of the spring. The rate creep that results usually stops after the first inch of spring travel and does not appear again until spring travel approaches coil bind. Generally speaking, this type of rate creep is of little consequence with springs softer than approximately 500#/inch. When you use springs stiffer than 500#/inch rate creep becomes more pronounced.

It is important for you to realize that springs will pick up rate during compression. Consequently, the rate marked on a spring can differ from the rate as seen by the chassis. This is especially true whenever a spring manufacturer rates springs based on the first inch of compression.

Example: A racer replaced a 720# coil-over spring with a 750# Afcoil. The racer believed he had stiffened his right front spring, however, the chassis behaved as though he had gone to a softer spring. Upon rating both springs, he found that the 720# spring was rated for its first inch of travel (720# in.) and produced a much higher (780# in.) rate for its second inch where it actually operated on the race car. Because Afcoils are designed to give their nominal rate closest to their actual working range of travel (this particular 750 spring rated 735# in. for its first inch of travel and 755# in. for its second inch), this racer actually softened up his race car even though the spring rate markings indicated the opposite! Rate creep can become even more complex and more difficult to monitor for racers using conventional type front coil springs designed with an open end coil(type 3). The lower control arms used with conventional springs typically incorporate a stepped helix spring seat built to an SAE specification (.720" of step). The helix seat was designed into lower control arms to insure consistent installation of the spring. Keep in mind that any rotation of the spring affects the actual installed rate of the spring.

Unless racing springs used for this type of application are designed with one end coil that closely matches the lower arm helix spring seat, a serious amount of rate creep can result. To minimize this type of rate creep, a conventional front spring should be wound with its bottom end closed so that it sits squarely in the helix seat. No active coil should touch the seat (just like the original production spring for which the control arm was designed -Type 2 spring).

When built in this manner, a coil springÂs only contact with the lower control arm is through an inactive (dead) coil (just like the spring's contact with the weight jack). Consequently, as the spring compresses, the number of active coils in the spring is not affected by the lower control arm. Therefore the spring's rate remains constant throughout normal suspension travel. Some rate creep still occurs due to contact between the dead end coils and the adjacent active coils as was explained earlier, but the amount of rate creep is miniscule compared to the rate creep produced by an open end coil spring. All AFCOILS, designed for use with stock lower control arms, are built in this manner.

If a spring has an open end coil(type #3), the open end coil is active but gradually deadens as the lower control arm moves against the spring. A considerable increase in spring rate occurs until the open end coil is completely seated in the helix.

For example, during a test a 1500# open end coil spring gained 464 lbs. of rate after 2 inches of spring travel. By comparison, a 1300# Afcoil (closed end coil spring) gained only 48 lbs. of rate after the same travel.

Further testing of a series of open end coil springs produced rate creep so inconsistent that at some points of spring travel the springs did not remain in the same rate order of softest to stiffest! It would be very difficult to make predictable handling adjustments using springs that exhibit such inconsistencies!

Keep in mind that any load change to an open end coil spring (via static weight, wedge, chassis roll, bumps, etc.) usually causes the spring's rate to change and, consequently, handling to change. If you are using open end coil springs you should chart their rates from static loaded height to fully loaded height weight(in one inch increments). You should compare this information before making spring changes. By now you should realize the importance of using springs that are designed to keep rate creep to a minimum.

What is Spring Stress?

As was pointed out earlier, the rate of a spring is determined by its diameter, the number of its active coils, and the diameter of its wire. Since most racing springs are built to a fixed diameter, a spring designer must decide on the diameter of wire and the correct number of active coils needed to produce the desired rate.

If the designer chooses a smaller than normal diameter of wire (which tends to soften rate), he will have to compensate by using fewer active coils (which tends to stiffen rate) to achieve the desired rate. There are two possible reasons for a spring designer to use a smaller than normal wire diameter for a specific rate spring:

Many racers mistakenly believe extra spacing between the coils of a spring indicates a preferable spring. While a spring must have sufficient stroke capacity it also must have sufficient material to absorb the load put onto it. If the spring's material is not sufficient for the load put onto the spring, the material will become over-stressed and the spring will take a set (lose height). Handling, of course, is affected and the reason is not always apparent to the racer unless he pays close attention to his springs.

Example: A typical asphalt late model set-up calls for a tremendous amount of load on the left rear spring (upwards to 600 pounds more weight than on the right rear spring). When the chassis sees normal spring travel, the cumulative load on the left rear spring produces a tremendous amount of stress in the spring. If the spring does not have sufficient material to handle the stress (as many don't), it will take a set (as many do) and the car will lose crossweight and tend to become loose off the corner. Excessive spacing between the coils of a spring is usually an indicator of a potential problem with spring stress.

Stress Consideration in Spring Design

Many times, because of the long stroke requirements for certain rates of racing springs, material strength must be sacrificed to achieve significant stroke. Couple this with the fact that the ideal wire diameter is not always made and you can see why some springs have a real potential to take a set. We have seen some brands of springs lose as much as 15/16" of free height during normal operation. To eliminate any set from occurring at the race track, it is good manufacturing policy to pre-set (press to solid height) all racing springs during their manufacture.

If done correctly, pre-setting will generally eliminate any potential for additional set, even when springs are designed with smaller than ideal wire. Shot-peening will further enhance a spring's durability. It should be pointed out that all Afcoils are pre-set and shot-peened during manufacture.

What if a Spring "Sets"?

When a spring takes a set it will normally stabilize at its new height. The rate effectively remains the same since no appreciable changes have been made to any of the three factors that determine the spring's rate. Other than creating a need to readjust the chassis (to restore the original set-up and ride heights) the spring should provide satisfactory performance. It is not uncommon for even well designed and properly manufactured springs to settle up to 1% of their free height. It needs to be pointed out, however, that in cases where a poorly designed spring is subject to extreme over-stressing, the spring's height may not stabilize. The spring may continue to change height (both shortening and lengthening) as the spring is worked. As a result, the set-up on the race car changes every time the spring's height changes. This can cause major chassis tuning headaches!

Monitor your Springs:

We recommend that you monitor the free heights of your springs on a regular basis. This is so important that some Indycar teams measure their springs' heights to the thousandth of an inch. Be sure to always measure height at the same point on the end coils(mark your springs to indicate the measuring point). You should suspect that a spring is setting whenever wheel weights continually change. Under no circumstances should springs be used that change more than 2% in height or do not stabilize in height. AFCOILS are guaranteed to maintain their free heights to within 2% forever!

At the least you should inspect all springs for free height changes after racing on a very rough track or if your race car was involved in a wreck. By now, you should realize there is much more chance for a spring to change its height than its rate. Consequently, you should spend your time monitoring your springs' free heights and not their rates!

What is Coil Bind?

Coil bind occurs whenever a spring is compressed and one or more of the springs active coils contacts another coil. The rate of the spring increases whenever a coil binds since the bound coil or coils are no longer active(this changes one of the three rate-determining factors). Of course, handling is affected whenever a coil binds. If the spring is compressed to solid height (all coils touching) during suspension movement, the suspension will cease to work. You can, and should, check for evidence of coil bind by examining the finish between the active coils. If any coils have bound the finish between them will show contact marks that appear as though they were drawn with a lead pencil. Normally any spring that is binding should be replaced with a taller spring. Be aware, however, there are racing springs on the market that are built with wire that is heavier than what's needed. These springs will coil bind before others that are built with the proper size wire.

Under very extreme conditions, coil binding can cause a spring to unwind slightly. This can cause the mean diameter of the spring to increase and reduce rate of the spring. You should realize that the potential for coil bind is increased whenever short springs are used. Always match the spring to the job.

Why Springs Bow:

Springs that have lengths greater than 4 times their diameter will have a natural tendency to bow when loaded. Consequently, tall springs tend to bow more than short springs, and small diameter springs tend to bow more than large diameter springs. Generally, the more a spring is compressed the more it will tend to bow. Keep in mind the rate of a spring will increase if an active coil rubs another part of the race car. Here are some tips to minimize bowing:

There are special manufacturing techniques that help to keep bow to a minimum. AFCOILS are built for minimum bow under all racing conditions.

Spring Checkers:

Unfortunately, we know of no reasonably priced spring checker that will accurately measure a spring for rate. We have tested most brands of checkers and cannot give recommendation to any. However, there are steps and procedures that can increase the reliability of the spring rate checkers commonly sold to racers. The accuracy of a spring checker should be monitored. This can be done through the use of a checking spring. A checking spring can be any spring that has been accurately rated at one inch (or smaller) increments up to a load close to the total capacity of the checker. It is important that the free length of the checking spring remain constant. The rates given by the checker can be compared to the known rates of the checking spring (at each increment of compression). Any rate discrepancies between the checker and the checking spring should be noted and taken into consideration when checking for rates of other springs.

AFCO can provide checking springs for this purpose. The repeatability of a spring rate checker should also be monitored. Simply put an old spring in your checker and preload it to at least 20 lbs. Then compress the spring and note gauge readings at 1" increments (or less) for the next three or four inches of spring travel. Tag the spring with this information and use it occasionally to check for repeatability. Make sure the free height of the spring remains constant. Do not use the spring if any change in free height occurs. A checking spring can also be used to check for repeatability. A rate checker should consistently repeat rates to within 2.5%.

SHOCKS

 

4-Bar Dirt (Aggressive)	2-Link Dirt (Aggressive)	Swing Arm (Aggressive)
LF-S7Z-3535 RF-S7Z-4545	LF-S7Z-3535 RF-S7Z-4545	LF-S7Z-3535 RF-S7Z-4545
LR-S9Z-2080 RR-S9Z-2020	LR-S9Z-4020 RR-S9Z-3030	LR-S9Z-4020 RR-S9Z-3030

SPRINGS

4-Bar Dirt	2-Link Dirt	Swing Arm
LF-650 lb RF-750 lb	LF-650 lb RF-750 lb	LF-650 lb RF-750 lb
LR-200 lbRR-175 lb	LR-200 lb RR-175 lb	LR-250 lb RR-225 lb

SHOCK

Stock Car GM Metric	73-77 Chevelle / Monte Carlo	70-81 Camaro
LF-AK 4040F RF-AK 3050F	LF-AK 4040F RF-AK 3050F	LF-AK 2072F RF-AK 2072F
LR-AK 3030R RR-AK3030R	LR-AK 3030R RR-AK3030R	LF-AK 1054F RF-AK 1054F

SPRING

Stock Car 2900 lbs	Stock Car 3400 lbs	Camaro
LF-900 lb RF-1100 lb	LF-1000 lb RF-1250 lb	LF-1000 lb RF-1150 lb
LR-250 lb RR-225 lb	LR-275 lb RR-250 lb	LF-200 lb RF-175 lb

The easiest way to estimate the 5-lug bolt circle, is to measure from the back of a hole to the center of the second hole.

Use different wheel off sets to help tune the chassis to track conditions. When you change wheel offsets, it changes the amount of weight the tire puts on the ground. You can tighten or loosen your car up by just changing wheel offsets. Please check the illustration below to measure offsets.