The most important starting point for this decision is to thoroughly know your baseline chassis setup, and then understand how each adjustment available to you will affect that setup. And it is extremely important to have the setup on paper so you can look at it and visualize the changes you can make.

Next you have to define what is happening to the chassis and where on the track it is happening. Let’s say the track is getting slick and the car is loose at corner entry and mid-corner. What you need is something that will make the right rear stick better through the first half of cornering. Stagger should already be reduced for a dryer, slicker track. What you are looking for is something that will create more right rear side bite and/or instantaneous weight transfer onto the right rear to make it stick. Look at these chassis adjustments:

1. Reducing air pressure in the right rear will create a larger tire footprint for more surface grip. It will also make the tire sidewall more flexible which allows the tire to roll under during cornering, moving the footprint in closer toward the car which will tighten it up.
2. Space the wheel in toward the car. This places additional weight loading on the tire and tightens the chassis.
3. Use a one step softer shock absorber valving at the right rear. This allows weight to transfer quicker to this corner.
4. Take chassis tilt out of the rear. This places more static weight on the right rear corner. This affects the car the most through the first half of cornering.
5. Move the wing back to load more down force at the rear tires.

Try these adjustments in this order, one at a time. Keep thorough notes on how the car handled, and track conditions, so you will have some experience to draw on in the future.

For more information, see #S282 Sprint Car Chassis Technology.

The pinion angle should be in the range of 5 to 8 degrees. Pinion angles do not have an effect on traction because they are not the limiting device on the rotation of the rear axle housing. It is the trailing arms that limit the housing rotation and transfer loading to the chassis. So the angles of the trailing arms are what have an effect on traction.

A small amount of pinion angle is set to prevent premature universal joint wear. The angle causes all of the rollers to roll properly and not flatten. On most types of rear suspensions the pinion angle is set by changing the length or angle of a trailing link. While this changes the pinion angle, it also changes the anti-squat of the rear suspension which affects forward drive traction. For example, shortening the length of the upper link on a 3-link rear suspension will add pinion angle, but it will also roll the top of the rear end housing forward which will increase forward drive traction.

If on the front of the car you have a 500 lb spring on the left and a 400 lb spring on the right, more weight is said to go to the stiffer spring, thus the left side. If this is correct, how do I explain the fact that the right front appears to be diving down more than the left?

Not true. Let's look at the basics. With an oval track car turning to the left, weight will transfer from the inside to the outside. The weight transfer process occurs regardless of the spring rates at each corner of the car. So, under normal circumstances with normal chassis settings, turning left will always make the right front corner dip.

In your section on "roll moment" [in the book #S192 Street Stock Chassis Technology], you state that the larger the roll moment the greater the body roll. Also, the greater the moment arm, the less resistance there is to body roll. How does this concept fit with the idea of "roll couple distribution"? You state on page 16 that the end of the car with the highest roll stiffness will receive the greatest amount of weight transfer during body roll. Am I confusing these concepts?

You are mixing two concepts together. The roll moment is the distance between the roll center or roll axis and the Center of Gravity Height. The greater this distance or the greater the separation between the roll axis and Center of Gravity Height (CGH), the greater the body roll. If, on the other hand, the roll center height and CGH are equal to each other, the sprung mass will not experience body roll because there is no lever arm or roll moment.

Roll couple distribution (RCD) is a totally different concept. When body roll occurs in a vehicle with suspension, something on the outside of the chassis has to resist the body roll. That is the springs. Whether the springs are stiffer in the front or in the rear defines the RCD. For example, if the total rate of the front springs is 2000 #/" and the total rate of the rear springs is 100 #/", the front of the car has a much stiffer roll resistance. The end of the car that has the most roll resistance handles that proportion of weight transfer caused by body roll. So in this case, 2000+100 = 2100 #/" total roll resistance. 2000 (front) divided by 2100 (total) = .9524, or 95.24% front roll couple distribution. Or in other words, 95.24% of all inside to outside weight transfer caused by body roll is handled at the front due to the spring rates installed there.

For more information, see #S192 Street Stock Chassis Technology.

We have a limited late model which does not have an anti-roll bar. How do I figure our roll couple? Also, what change on our car would be comparable to that of the anti-roll bar? Or what change could we make that would not affect any other facet of the chassis?

See the example in the previous answer. Roll couple is computed by adding up the wheel rates of all springs -- in the front, the left and right front springs and the anti-roll bar, and in the rear, the left and right rear springs. Adding all five of these numbers together produces the total roll resistance. Now divide the total front combined wheel rates by the total roll resistance. This gives you the front roll couple distribution percentage.

If you don't have a front anti-roll bar, just leave the wheel rate of the anti-roll bar out of the calculation shown above. You just have four springs (LF, RF, LR, and RR) instead of five (the four previously listed plus the anti-roll bar) in the calculation.

Without an anti-roll bar in the chassis, the only way to make chassis changes would be:

1. Change spring rates at the RF and RR to influence roll couple, or oversteer/understeer.
2. Change cross weight
3. Vary left and rear weight distribution
4. Change stagger

For more information, see #S192 Street Stock Chassis Technology.

For more information, see our book #S239 Paved Track Stock Car Technology

Mounting the lower links like this can have an effect on both material strength and geometry. Forces during acceleration, braking and cornering place torques on the rear housing in three different directions. The three links resist these torques and keep the rear axle controlled and in place. The farther the two lower links are placed from the center of the housing (in other words, as close to the tires as possible), the better the leverage the links have on the axle. The closer the links are placed to the center of the housing, the more forces they have to handle. As an example, think of a teeter-totter. If you stand behind it and move one end up and down, the force required to do that isn't too much. Now, move to the center pivot point, grab the plank just to one side of the pivot and move the teeter-totter up and down. You will find that requires quite a bit more energy and strength to do. The same effect happens when you move a lower link in closer toward the center of the axle housing. The link mounted closer to the center of the housing will have heavier torque loadings imposed on it, so it will be more vulnerable to breakage. The link material and the rod ends will have to be much stronger to prevent breakage.

Mounting the lower links like this can also have an effect on geometry. The two lower links are what push the chassis forward. If the left side link is offset toward the center of the rear housing, then the reaction forces that load the rear end are offset toward the right. So under acceleration, these forces will load the right rear heavier. It would be like jacking weight onto the right rear. It would tend to loosen the chassis under acceleration at corner exit.

One more item: these same forces under acceleration could flex or bend the left side rear axle housing tube. That is because the left lower link is connected near the center of the housing and the driving force (the left rear tire) is at the outside of the housing. With no support at the outside of the housing, the forward driving force can cause a bending moment in the housing tube about the inner link connection point.

For more information, see #S192 Street Stock Chassis Technology.

For more information, see #S280 I.M.C.A. Modified Racing Technology.

Here are the adjustments you can make, in the order of importance, with an explanation of how they effect the handling:

Note: All of these chassis adjustments (except #5) would apply to any dirt track stock car, such as a sportsman, late model or IMCA modified, experiencing the same handling problem.

1. Increase stagger. Stagger loosens up the chassis through all three phases of cornering, but it has its greatest effect under acceleration. Many racers take out too much stagger when the track gets dry slick.
2. Decrease cross weight (RF/LR weight bias). Having more weight load on the left rear makes the car tend to drive straight ahead under acceleration.
3. Use a softer left rear spring or torsion bar rate. Under acceleration, a stiffer left rear spring functions just like having more cross weight. It makes the left rear more dominant and drives the car straight ahead.
4. Don't use easy-up shocks in the front. An easy-up shock allows weight to transfer very quickly from front to rear under acceleration due to softer rebound valving. With easy-up shocks, the rear tires are more heavily loaded which produces more forward traction. At the same time, unloading weight from the front tires reduces grip on them.
5. Lower the front Panhard bar. This lowers the front roll center, which loads the right front tire harder during cornering.

For more information, see:

More shock rebound control on the left side will help to loosen the chassis at corner entry, and into mid-corner. It keeps the left side tied down longer during corner entry. This shifts braking influence to the left side tires at corner entry. This increases braking influence on the left side which helps to turn the car to the left.

Softer compression/stiffer rebound at the left front allows the left front corner to compress more easily at corner entry and keeps that corner tied down. That helps the car steer more easily into the corner.

For more information on chassis tuning with shock absorbers, see:

There is a lot of difference of opinion on this. Some chassis builders and top racers say "yes," others say "no." Those who say "no" say that you can use one set of percentages (left side and rear) for the car without the drivers, and another set for the car with the driver. That's too confusing. In our opinion, always scale the car with the driver's weight in the car. After, all, that is what the race car sees on the race track. Put ballast that equals the driver's weight in the driver's seat when scaling the car. Furthermore, make sure all fluids are full(oil, water, power steering fluid, transmission fluid, etc.), and the fuel cell should be 50 percent full.

For more information on scaling a race car, see:

First, the left side percentage should be right at the maximum allowable, or 56%. For left side weight on a paved track, more is better. More static left side weight keeps more weight on the left side tires during cornering. More left side tire loading during cornering (and thus less right side) improves cornering grip at all four corners of the car.

Rear weight percentage should be 50.5% to start.

Doing the math for your situation, you have to have a minimum weight of 2,800 pounds with driver and all car fluids. Add 10 pounds for a safety factor, so 2,810 pounds is your target weight. The driver weighs 180 and your finished car (less ballast) is 2,480, so 2,810 less 180 less 2,480 equals 150 pounds of ballast required.

The ballast must be mounted as low in the chassis as possible to help keep the center of gravity height (CGH) as low as possible. The lower the CGH, the less weight that will be transferred from inside to outside during cornering.

Place your car on wheel scales and start adding ballast to the left side until the scales show that you have achieved the left and rear percentages that you want. When placing the ballast, keep it concentrated in as small an area as possible, and as close to the center of gravity as possible. For example, you could achieve the same left side percentage by putting a 75-pound block at the front of the left side frame rail and a 75-pound block at the rear of the left side frame rail. But the car is going to be faster if these two blocks are brought together and placed in the mid-frame rail area near the CG of the car. That is because of an effect called polar moment of inertia. It deals with the willingness of the chassis to change directional attitude. In other words, it is much easier for the chassis to change directions when the weight mass is concentrated nearer to the center of gravity. By having the weight mass concentrated closer to the CG, it is easier to move and control the weight during cornering and deceleration/acceleration. The chassis will be more responsive. It is not as reluctant to change direction, and the springs and shocks will have an easier time controlling the dynamic weight movement.

For more information, see #S239 Paved Track Stock Car Technology.

For short track cars, adding a rear anti-roll bar is used to help the car to turn in to a corner and through the middle of the corner. The spring rate of the bar is added to the existing left rear and right rear spring rates of the car, making the rear roll couple percentage stiffer during cornering. This works best with cars racing on shorter, tighter and/or flatter tracks where making the car turn-in crisply is difficult. The rear bar helps to free up the car at entry.

The added spring rate of the rear anti-roll bar only comes into play as the body rolls during cornering. Without changing rear spring rates, a typical rear anti-roll bar has a spring rate of around 100 pounds per inch. This would be a 24-inch effective length bar, 0.75" O.D., with 12" arms. Using a longer arm length (in the 10 to 14-inch range) is best, because a shorter arm length wraps up the bar too quickly, making the car get loose quickly. Using a rear bar usually requires more cross weight in the car for corner exit. However, if a slightly stiffer rear bar is used in conjunction with slightly softer rear spring rates, the rear of the car will squat more under acceleration, which will aid forward traction.

With free play you have no preload. Adding preload adds cross weight into the chassis. Also, the sway bar does not become an effective part of the suspension system until this free play is taken up by movement.

For more information on street stocks, see #S192 Street Stock Chassis Technology.

The formula to use is:

Final ratio = (Average RPM) x (Static tire radius)

(Average Speed) x (168)

Looking at the information you provided, the number you are using for the average RPM is too high. The AVERAGE RPM is RPM at the lowest point when you start to accelerate off a corner plus the highest RPM when you shut off for the next corner, divided by 2. In your case, your average RPM should be more like 4,800. Let's say your top RPM is 6,000 and your low RPM when you start to accelerate out of a corner is 3,600. 6,000 + 3,600 = 9,600. 9,600 divided by 2 is 4,800. If your average RPM is really 6,000, you would have to be turning your motor up to about 8,400 RPM at the end of the straight.

If we use 4,800 as your average RPM in the formula, your final gear ratio works out to 7.00. The math:

Final ratio = 60,000

8,568

Final ratio is 7.00

58% is a lot of cross weight. 56.0 to 56.5% might be better for you, especially if your car is on the tight side. In an ideal situation, you will probably see the RF/LR diagonal about 5% to 7% warmer than the LF/RR diagonal.

For more chassis tuning information, see #S239 Paved Track Stock Car Technology.

Only testing will tell you for sure. There are racers running similar cars who use a pair of 300s or a pair of 325s across the front. But the total setup has to be adjusted to make it all work together. You can't let just one aspect of your setup package become a priority. Everything has to work together -- front and rear. If you soften the front springs, and nothing else, it will make the car looser. If you soften the front springs, the rear springs have to be softened a proportionate amount to keep the handling balanced. The next question is why should the springs be softened? Using softer springs creates more downward loading on the outside tires. This helps create increased grip with harder compound tires or on a slicker track surface.

For more information, see #S239 Paved Track Stock Car Technology.

Yes, it will handle differently because air pressure adds spring rate to the tire. More air pressure makes the tire stiffer. So using 30 psi at the right rear instead of 24 psi will make the car tend to be looser, with all other variables remaining the same. The other thing to consider is the amount of air pressure used at the left rear and right rear to create the required amount of stagger. It is a higher priority to use the difference between left rear and right rear tire pressures to achieve the required stagger than to worry about tire spring rates.

For more information on tires and chassis tuning, see #S239 Paved Track Stock Car Technology.

The following answers are based on using a true torque sensing differential such as a Diamond Trak from Quick Change Exchange or a Gold Trak from Dan Press Industries. In general, it will allow you to use less stagger. A torque sensing differential provides each rear wheel with the RPM difference required for the turning radius required at each rear wheel. It senses wheel slip and delivers torque to the wheel with the greatest amount of traction. The advantage is that as a car enters a corner, neither rear wheel is completely unlocked. There will still be some torque loading of the outside wheel. This keeps the car tighter going into the corner. This also means less stagger is required to turn the car as compared to a spool. And this means less right rear tire heat and wear.

For more information on various stock car differentials, see #S239 Paved Track Stock Car Technology.

There are several approaches, but what you want to do is make an adjustment that will primarily affect the car at corner entry, and not affect it at mid corner and corner exit. For instance, you could lower the rear J-bar, but that will tighten up the chassis at exit as well.

Try these adjustments:

1. Using a softer spring rate at the left front corner will loosen up the chassis at corner entry. Start with a spring rate that is 100#/" lighter. The softer left front spring compresses more at entry, which unloads the right rear more. The effect of the left front spring rate is felt by the chassis primarily at corner entry so changing it will not have a big effect on the handling at mid corner and corner exit like changing cross weight or ballast position would.
2. Add more crossweight by adjusting at the left rear. This will loosen the car at corner entry, but it will also tighten it up at corner exit under acceleration.
3. The axle damper shock may have too much uphill angle. Usually an uphill angle of 5 to 8 degrees is used to combat rear end looseness at corner entry. Try less angle. If you have to mount the shock at less than 5 degrees, try taking it off the car.
4. Use a left front shock that is one to two steps softer on compression.

Decrease rear stagger by decreasing right rear air pressure. This tightens up the chassis two ways: First, less stagger makes the car tighter. Second, with the right rear tire being lower (smaller rolling radius), the chassis gains cross weight, which tightens the chassis. Plus, the lower right rear tire pressure helps improve right rear grip.

Yes. The greater the banking of the race track, the less rear stagger required. For example, a flat track might require 3 ½ inches of stagger, whereas an 18-degree banked track with the same car may require on 1 to 1 ½ inches of stagger.

Paved track chassis tuning is covered in #S239 Paved Track Stock Car Technology.

Moving the right rear wheel outward from the chassis centerline decreases weight loading on it, while moving it inward closer to the chassis increases weight loading on it during cornering. Loosen up a car by moving the right front in and the right rear out. Tighten up a car by moving the right front out and the right rear in. On dirt, moving the right rear out frees up the chassis when the track is sticky or rough. Moving the right rear in when the track gets slick tightens up the car.

Chassis tuning with wheel spacing is covered in several of our books, including:
#S196 Stock Car Dirt Track Technology

A tire heat cycle is when a tire is brought up to operating temperature and run for some laps, then allowed to cool. Taking a tire through a heat cycle changes its chemistry. In most instances it stabilizes the tire compound by decreasing its heat generation. But that process also slightly increases the durometer hardness of the tire. So scrubbing the tires (one heat cycle run) will help the tires run a little cooler and wear slightly better.

Successive heat cycles will continue this curing process. Eventually the tires will not provide nearly enough grip because they have gotten too hard, but they will wear like iron. Each heat cycle cures the tire rubber more and makes it harder.

Keep good records on each of your tires so you know how much use -- and how many heat cycles -- each of your tires has.

Racing tire technology is covered in several of our books, including:
#S239 Paved Track Stock Car Technology

1) Setting A-arm angles is a shortcut that chassis builders use to set ride height. The angles are only valid for that particular chassis design. There are many factors that can affect the angle, such as inner mounting point heights, spindle height, etc.

2) The driver, or ballast equaling his weight, must be in the seat then setting ride height and corner weights. The driver’s weight will affect the weight and height at each corner.

3) Set your target ride heights, then set corner weights and cross weight. Don’t change ride heights after that or you will change the corner weights and cross weight.

Scaling the car and setting the ride height is covered in several of our books, including:
#S192 Street Stock Chassis Technology

It is correct that the lower A-arm pivot points should be parallel to the centerline of the chassis. But that is if you are building a tube frame car and can control how things are designed. In your case, you are stuck with what GM has built.

In the top view, you have to mount the upper A-arms at the same angle as the lowers. This way the upper and lower arms move parallel to each other in bump and rebound. If the lower A-arm is mounted at the stock angle and the upper is mounted parallel to the frame rail and chassis centerline, the caster gain during cornering will be severe.

If you need a really good tool that will help you work out the optimum front suspension geometry, use our #C249 Front Suspension Geometry Pro computer program. It allows you to enter all the values you currently have, then it analyzes the geometry. Then you can play “what if” and change dimensions and see if it improves the front geometry. This way you can have your front geometry all worked out before you ever cut and weld.

Using a stiffer spring rate at the left rear gives more forward bite under throttle application at corner exit. It makes the car tighter. If you need more forward grip, this is the way to go. However, if your car pushes under throttle at corner exit, use the stiffer spring at the right rear.

Chassis tuning and adjustment is covered in several of our books, including:
#S192 Street Stock Chassis Technology

Adding a rear spoiler adds downforce onto the chassis, which adds downforce or vertical loading onto the tires. This loads the rear tires downward to increase tire grip. Slip angle increases primarily due to lateral loading of the tires during cornering. Vertical loading will increase tire grip, up to a point where total loading of the tire exceeds the maximum coefficient of friction of the tires. Front/rear roll couple has to be adjusted to balance the chassis and slip angles.

Also note that vertical loading due to the spoiler adds downforce equally onto the left rear and right rear tires. This adds downforce and grip onto the left rear as weight is being taken off of it due to weight transfer during cornering. More loading on the left rear will make the car tend toward pushing, or take away a loose condition.

Tire technology is covered in several of our books including:
#S196 Stock Car Dirt Track Technology

The rod pressure in a gas pressure monotube shock increases when the shock heats up, and this increases the spring rate of the shock. However, if a racer chooses a monotube shock which uses a base valve, the internal gas pressure can be drastically reduced. This greatly reduces the spring rate build-up in the shock.

A base valve puts a shim stack between the piston/rod assembly and the floating piston. This helps to keep some pressure on the shock fluid during compression without the need for higher gas pressure behind the floating piston.

For more information on base valves and monotube gas shocks, see #S296 Midget Chassis Technology

I have been reading your book Street Stock Chassis Technology, and I have a couple of questions. 1) On page 9 it says "A vehicle with no suspension will transfer the same amount of weight laterally as a car with suspension if these three above stated factors (lateral acceleration acting against the CGH, the height of the center of gravity, and the vehicle track width) are the same." Are you saying that a set amount of weight, depending on those factors mentioned, is going to transfer, no matter what?

2) Also on page 9 it says, "We want most of the weight transfer to take place through the suspension and springing system, as chassis roll." How else, and where else, would this weight transfer take place if not through the suspension system?

1) Yes. A vehicle does not have to have a suspension system in order to experience lateral weight transfer during cornering. A go-kart with no suspension system experiences lateral weight transfer during cornering.

2) When weight transfer is reacted in the vehicle as chassis roll, this is the lateral acceleration acting on the sprung mass of the vehicle. But lateral acceleration also is reacted through the unsprung mass of the vehicle. For example, the rear end housing and tires are subjected to lateral acceleration also.

For more information, see #S192 Street Stock Chassis Technology

The anti-roll bar can be placed in front of or behind the axle with no effect on the rate or how the bar acts, as long as the bar arms are the same length when mounted in one direction or the other. It is just a straight spring being twisted by a lever arm.

The same thing applies to the vertical mounting height of the bar, as long as the bar arm length remains the same in all cases.

When an anti-roll bar is attached to a solid axle, D1 is the distance between the attaching points of the arms to the axle. D2 is the track width of the axle (that is, the centerline of the left tire to the centerline of the right tire). To calculate effective spring rate of the bar, divide D1 by D2 and square the answer, then multiply this by the spring rate of the bar.

You can find more information on straight axle suspension geometry in these books:
#S282 Sprint Car Chassis Technology

There are two advantages: 1) The GM metric spindles will bend easier than the Pinto spindles or the Impala/Caprice spindles; and, 2) Pinto spindles are lighter than the Impala/Caprice spindles. The metric spindle, rotor and caliper combination weighs the same as a Pinto spindle, Granada rotor and metric caliper combination (about 40 pounds), but the Impala spindle, rotor and caliper package is nearly ten pounds heavier.

The common Pinto spindle installation uses a 1974 to 1980 Pinto spindle (which is different than a 1971 to 1973 Pinto spindle), with a 1975 to 1977 Granada (or Monarch) hub/rotor. The Granada hub bolts right on to the Pinto spindle. AFCO sells a caliper bracket that adapts the GM metric caliper to the Pinto spindle.

The Granada rotor has an 11-inch diameter and is .875-inch thick. It uses a 5 x 4 ½ bolt pattern. These rotors are becoming difficult to find in junk yards, but a new part is being manufactured by US Brake (part number 9850-6510). It is a stock appearing hub/rotor, but comes standard with a 5 x 5 bolt pattern with 5/8” course studs installed. It also is pre-drilled with a 5 x 4 ½ bolt pattern.

With the Pinto spindle, use a Moog K772 upper ball joint (same as AFCO’s 20034), and a Moog K5103 lower ball joint (same as AFCO’s 20033). The lower ball joint hole has to be reamed to fit this ball joint taper.

One important design consideration when using the Pinto spindle is that it is 1.125-inch shorter (overall) than the metric spindle, and 1.0625-inch shorter from the center of the pin to the top of the spindle. This will change the roll center height and rate of camber change during bump travel.

For more information, see #S280 I.M.C.A. Modified Racing Technology

Fortunately there are some Carrera dealers that still have these parts in inventory. One that we have found that still has them is: Ellis Engineering 2304 Grimmersborough Lane Charlotte, NC 28270 (704) 393-9054 www.sellisengineering.com

When purchasing the strut cartridge (which is the shock absorber element), use part number 32743a6 instead of the 31663a6 recommended in the book. The 31663 was recommended to us by the Carrera tech staff, but after using it on our project car, the driver felt that it was too stiff. After installing the 32743 cartridge, the driver said the car felt more comfortable, it stuck better at corner entry and mid corner, and he backed that up with faster lap times.

For the rear shocks, you can use the street stock-style rear shocks from PRO Shocks. The part number is SS400.

Other alternatives for the front strut and cartridge: Racer Walsh 1849 Foster Dr. Jacksonville, FL 32216 800 - 334 - 0151 904 - 721 – 2289 www.racerwalsh.com Their catalog lists a front adjustable strut for the Mustang. The part number is HALH2001.

KYB has a replacement strut and cartridge for the Mustang. It is in their GR-2 line which is for GT and Special Handling (high performance) models. The part number 235005. More information at www.kyb.com.

Tokico also makes a replacement strut and cartridge. The part number is HB3026. It is a non-adjustable gas shock. Their website is www.tokicogasshocks.com.

NO! Monotube gas shocks have an internal pressure to prevent the shock fluid from foaming. But the gas pressure also has an influence on the extension of the shock and the rate of the shock. Your shock absorbers are a part of the total suspension package of the race car, and so the car should be scaled with the shocks in place. The car should be scaled with everything on the car exactly as it will be when the car first hits the track. The total amount of gas pressure in a shock also has an influence on total spring rate at that corner of the car. More gas pressure produces more spring rate.

For more information on monotube gas shocks used on a stock car, see #S298 Dirt Late Model Chassis Technology

With the stiffer spring installed on the right rear, the car will tend to be looser at corner exit. The greater the banking angle of the track, the more the stiffer right rear spring will loosen the car. In general, most paved track baseline setups start with a left rear spring that is 12 to 15 percent stiffer than the right rear.

Chassis tuning and adjustment is covered in several of our books, including:
#S192 Street Stock Chassis Technology

First of all, let’s define sway bar preload and what it does. A twisting force can be added to the sway bar as the car sets in its static (non-moving) condition. This is done either by changing the length of a threaded link which attaches the bar to the lower control arm, or by raising or lowering a load bolt which attaches the sway bar to the chassis. Adding preload (pre-set twisting force on the bar) adds cross weight to the chassis. Usually a chassis is set up with the sway bar neutral (no preload) or up to 1% preload. The amount used is part of a baseline setup, and is learned with on-track experience and driver preference.

The preload is set when the car is on the scales. If a 1% preload is desired, the adjuster is screwed down until the scales show that 1% more cross weight has been added. Many times racers will start their baseline setup with neutral preload, but they know that adding 1% preload at the track will be a quick and easy way to tighten the chassis. In this case, set the preload with the car on the scales, and count how many turns on the adjuster are required to get the 1%. Then write this number down in your setup notebook so you can quickly add it at the race track if needed. Then the bar can be restored to the neutral condition.

For more information on chassis tuning with sway bar preload, see:
#V191 Street Stock Chassis Set-Up & Adjustment DVD

Monotube shocks offer a revalvable design, which means that the racer can disassemble the shock and change the compression and rebound damping control values. You can also change the pistons to make the shock linear or digressive. If you are going to revalve your own shocks, you need a shock dyno to test the shock to make sure the changes you made are what you desire.

Monotube shocks are much more efficient in dissipating heat. Less heat in the shock oil means more control and less fade. Both types of shocks, when used in one given situation, will generate the same amount of heat. But the twin tube shock will generate the heat in the inner working tube, and this inner tube is surrounded by hot oil in the outer tube. That makes it more difficult for heat to radiate out of the shock body. A monotube has only the outer tube so it is easy for heat to radiate out of the tube wall.

Monotube shocks, in general, are almost always lighter in weight than twin tube shocks.

Twin tube shocks are almost always less expensive than monotube shocks. Sometimes there is a considerable difference in cost. Let your budget be your guide.

For more information on shock absorbers and chassis tuning with shocks, see:
#S282 Sprint Car Chassis Technology

ARS shocks are manufactured by Advanced Racing Suspension in Indianapolis, IN. They have been in business for many years. Their products have been very successful on midgets, sprint cars and Silver Crown cars. They started out as a rebuilder of Carerra shocks, revalving the Carrera shocks to meet specific applications. When QA1 purchased Carrera, they began building all of their own shock components and complete shocks. They build both twin tube and monotube shocks, and have shocks available for all forms of racing – dirt and asphalt sprint cars, dirt and asphalt midgets, pavement late models, dirt late models, mini sprints, and even quarter midgets.

ARS shocks are built very specific to their application on a particular race car, and their part numbering system reflects this. This can make decoding their part numbers a bit difficult at times. Below is a guide to the ARS part numbering system.

Shock Type

1000 Series – small body twin tube shock Threaded aluminum body, revalvable, either non-adjustable or rebound adjustable, available in 5", 6", 7", 8" and 9" strokes.

2000 Series – large body twin tube shock

Threaded aluminum body, revalvable, either non-adjustable or rebound adjustable, available in 5”, 6”, 7”, 8” and 9” strokes. Available with E, A, B, ARC and BRC features (see below for definitions).

3200 Series – small body monotube shock with base valve

Threaded aluminum body, revalvable, either non-adjustable or rebound adjustable, available in 5”, 6”, 7”, 8” and 9” strokes. Available with E, A, B, ARC and BRC features (see below for definitions). The use of a base valve allows use of low internal pressure.

4000 Series – large body double adjustable monotube shock

Threaded aluminum body, revalvable, adjustable separately for rebound and compression, available in 4”, 5”, 6”, 7”, 8” and 9” strokes. Available with E, A, or B adjustment features for rebound (see below for definitions), and adjustable for compression at the remote reservoir.

4200 Series – large body monotube shock with base valve

Threaded aluminum body, revalvable, either non-adjustable or rebound adjustable, available in 5”, 6”, 7”, 8” and 9” strokes. Available with E, A, B, ARC and BRC features (see below for definitions). The use of a base valve allows use of low internal pressure.

Features Decoding

A – cockpit rebound adjustable; cable is parallel to shock mounting bolt

ARC – cockpit rebound adjustable; cable is parallel to shock mounting bolt; adjusts rebound and compression at the same time in proportional ratios

B – Cockpit rebound adjustable; cable is 90 degrees to shock mounting bolt

BRC – Cockpit rebound adjustable; cable is 90 degrees to shock mounting bolt; adjusts rebound and compression at the same time in proportional ratios

E – Rebound adjustable at the shock mounting eye

E/C – 2 separate adjusters. Uses an adjuster on the shock eye for rebound and a second adjuster for compression on the remote canister.

O.W. – specifies a different amount of bleed orifice size in main piston

RT – rough track valving. A shock is valved to be one valving code at low speed shaft velocity and one step stiffer valving code at higher speed shaft velocity.

SPL – Uses a 1-inch shorter shaft than the body is designed for, which allows for more gas expansion inside the shock. For example, a 7-inch shock body using a 6-inch shaft.

ARC Sample Part # Decoding

1072/4

10 = 1000 series shock

7 = 7” stroke

2 = 2 rebound valve code

/4 = 4 compression valve code

3271/4

32 = 3200 series shock

7 = 7” stroke

1 = 1 rebound valve code

/4 = 4 compression valve code

E3274-0.5/3

E = rebound adjustable at eye

32 = 3200 series shock

7 = 7” stroke

4-0.5 = rebound adjustment range from 4 valve code to 0.5 valve code

/3 = 3 compression valving

B1078-2/3

B = cockpit rebound adjustable

10 = 1000 series sock

7 = 7” stroke

8-2 = rebound adjustment range from 8 to 2 valve code

/3 = 3 compression valving

E4257-4.5/5.5 O.W.

E = rebound adjustable at eye

42 = 4200 series shock

5 = 5” stroke

7-4.5 = rebound adjustment range from 7 to 4.5 valve code

/5.5 = 5.5 compression valving

O.W. = main piston has one 0.006” bleed orifice

You can find more information on shock absorbers and tuning a chassis with shock absorbers in one of these books:
#S239 Paved Track Stock Car Technology

Traction can be increased by using softer spring rates at all corners of the race car. That allows the tires to “soak up the track” for more grip. But a byproduct of using softer springs is increased body roll. Body roll has to be limited at some point or else chassis attachment linkages will be at unacceptable angles, which will significantly reduce handling performance. So a much stiffer-than-normal front anti-roll bar (sway bar) is fitted to the chassis to control excess chassis roll.

That is the basic thinking behind the newest BBSS setups, but it takes many more elements in the chassis to make this setup work For example, the right rear spring rate is crucial to balance the front sway bar rate. And the valving stiffness of the shocks, and the rebound and compression ratio of each shock, is critical to making this setup work. And there are many other things in the chassis that have to be adjusted or changed to make the BBSS setup work properly.

For more information, see #S295 Paved Track Big Bar Soft Spring Setups.

Sorry, you will just have to do your homework. The computer programs do a great job of simulating front end geometry or rear end geometry, or race car track performance dynamics, or a starting setup for your car on a specified track. But to get valid data that is usable for your particular race car, you have to enter in all of the required measurements for your particular car. Even if you have a manufactured chassis, your car is still different than any other car. There is no shortcut. You have to enter all of the measurements for your car in order to get the correct results. Like anything in racing, it takes time and effort to get positive results.

And speaking of taking measurements, it is extremely important to take the time to take accurate measurements. It isn’t easy to take measurements – especially side to side – because so many components are in the way. It takes time and care to be accurate. But the degree of accuracy in measurement equals the degree of accuracy of the computer program output. Remember, there is no shortcut if you want accurate and usable results.