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Welcome to our Frequently Asked Questions page. Here you will find answers to some of the questions you may have. If you don't find an answer to your questions, please feel free to send us an email at

Please click on a question to view the answer.

Q: Anti-Sway Bar Information
A: Anti-sway bars can be made of solid bar stock or tubing, bent into the proper shape with arms at approximately right angles to the chassis-mounted section of the bar.

Roll couple distribution is the combined resistance to body roll provided by the springs and anti-roll bars at the front versus the rear. Even though anti-roll bars distribute transferred weight differently than springs, the effect is the same. If you stiffen the front anti-roll bar, the understeer is increased (or oversteer decreased). If you stiffen the rear anti-roll bar, the overstreer is increased (or understeer decreased). Softening a bar has the opposite effect.

If a car oversteers during steady state cornering, a softer rear anti-roll bar should help reduce or eliminate the condition. Which bar to change depends on several factors.

There are situations where increasing the stiffness of an anti-roll bar will have the opposite effect. Most stock vehicles have excessive understeer because it is easier to control and provides more stability for the average driver than a vehicle that oversteers. A big part of this comes from excessive body roll, which induces too much camber change, and a good portion of the front tire contact patch loses contact with the road.

In this instance, adding a stiffer front anti-roll bar which would typically increase the extreme understeer, actually reduces the understreer by reducing the body roll induced camber change. The front tires now stay in better contact with the road surface, creating more traction and reducing understeer. This is an old trick in SCCA auto-crossing in stock classes where the few modifications permitted include changing the front anti-roll bar.

On a front drive car with a front weight in excess of 59 percent, the rear bar will be quite stiff. For competition, the bar will be stiff enough to lift in the inside rear tire contact patch off the ground slightly in a corner at the limits of traction. For the highway, the bar should be softer for improved stability.

Q: Anti-Sway Bar Rates
A: Four factors determine the rate of an anti-roll bar: the diameter of the bar along its active length, the length of the anti-roll bar arms, the active length of the anti-roll bar, and the modulus of elasticity (strength) of the bar material. Stiffness increases at a rate of four times the increases to the bar's diameter, thus doubling the bar diameter makes the bar eight times stiffer. The active length of the roll bar and the length of the arms operate in linear fashion, with shorter length increasing stiffness and longer length reducing it in both cases. The modulus of the material, which is nearly always high tensile strength steel, is considered a constant.

Because of multiple bends in a stock replacement anti-roll bar, it is difficult to calculate the rates. Most manufactures calculate the rates then check the actual rate of the bar mechanically. Adjustable anti-roll bars have multiple mounts on the arms to change the arm length and therefore the bar rate.

Q: Can I install the springs myself?
A: We don't know! Can you? How much mechanical experience do you have? Suggestion: Buy your vehicle shop manual and review the related sections. Proper installation requires specialized equipment. It is recommended that an experienced installer perform the swap. Remember, you also need someone to perform the wheel alignment.

Q: Can I use my stock shocks/struts?
A: It's recommended that you change them to achieve maximum ride quality, performance, and save labor dollars (and/or your time). Call or e-mail ( for shock/strut recommendations toll free at 800-905-6687.

Q: Do I need to align my car after installation?
A: Absolutely; whenever the suspension is changed or repaired it is crucial to have the alignment checked/corrected. If you are looking for specific, performance alignment recommendations for your car e-mail us ( or call 800-905-6687.

Q: Does cutting my springs void my Progress warranty?
A: Yes. All Progress Spring kits have a Limited Lifetime Warranty to the original purchaser of the product. However, The Progress Group WILL NOT warrant any springs that have been cut.

Q: For additional high performance handling information we suggest reading the Mike Kojima, Sport Compact Car Magazines' articles entitled Making it Stick that can be found here:

Q: How do I convert spring rates from kg/mm to lb/in?
A: Go to and type in "xxx kg/mm to lb/in" or "xxx lb/in to kg/mm" and Google will calculate the answer for you and it will appear above the search results. *Note: Replace the x's with real numbers!

Q: How do rear sway bars work on a FWD car with a torsion beam rear end?
A: By reducing deflection of the beam and therefore reducing body roll.

Q: How low is my car going to sit?
A: Each application varies; the lowered amounts are listed on the individual spring pages in our online store. Remember, we build true "Sport Springs", not just "lowering" springs. A true sport spring must take into account the performance and ride quality of the vehicle. Our design team engineers each application to achieve the right balance of handling, comfort, and appearance. To have acceptable ride quality, the vehicle cannot be "bottomed out." Many competitors "super-low" springs eliminate upward wheel travel, and ruin ride quality. Many "cut" springs ride poorly for the same reasons.

Q: My car sits crooked, what's wrong?
A: This is usually an installation error. The bumpstops must be trimmed (our instructions show you how), and the springs must be properly installed in their perches. Also make sure that you re-assemble the shocks and struts correctly, using all the necessary factory parts (Hondas and Acuras have special washers on the struts that must be put together correctly or serious suspension damage can occur).

Q: My lowered car is "bouncy"
A: This is usually a sign of worn-out shock absorbers (struts), or shocks that don't have enough rebound damping. We recommend that you use a true performance shock absorber, not a bargain brand. Call or e-mail ( our technical staff for recommendations at 800-905-6687. Bouncing can also be caused by over-lowering (cutting coils), or by not trimming the bump stops.

Q: Shock Information
A: Shock Compression and Rebound Damping

Bump, or compression, occurs when the shock shaft is being moved into the body. This occurs on the front of a bump, the back of a rut, the right side when turning left, the left side when exiting a left turn, the front under braking, and the rear under acceleration.

Rebound, or extension, occurs when the shaft is being pulled from the body. This occurs on the backside of a bump, the front of a rut, the left side shocks in a left turn, the right side shocks exiting a left turn, the front under acceleration, and the rear under braking.

How Shocks Affect Handling

The low- and medium-speed valving of the shock controls how fast weight is transferred. This affects the load on the tire and can change the handling balance while weight is being transferred. Once all weight has been transferred, the shock now longer influences handling. Since weight is almost always being transferred, the shocks are almost always affecting handling balance.

In general, rebound damping controls how fast weight leaves a tire while bump damping controls how fast weight goes onto a tire. Stiffer valving causes a shock to react more quickly; softer valving slows the reaction of the shock. Stiffer valving gets the load to change more quickly. Stiffer rebound valving gets the load off a tire more quickly and onto an opposite tire faster. Stiffer bump valving gets the load onto that tire faster. If all the valving, both bump and rebound at all four corners, changes equally, there is no effect on handling balance. If only bump or rebound is changed, then there is an effect. If only one end or one corner is changed, there is also an effect.

Analyzing Shocks

Shocks should be checked regularly for binds and pitting in the shafts. It is a good idea to check for dead spots by extending the shock fully and putting a sudden load on the shock by hand. Do the same with the shock fully compressed and pull out the shaft abruptly. A dead spot will be obvious, and that shock needs to be replaced or rebuilt.

Q: Spring Information
A: The heart of a suspension system is the springs. Springs perform five critical jobs. First, they keep the chassis and suspension from bottoming out over bumps. Second, they control the tires over bumps. Third, they control body roll during cornering, chassis squat during acceleration, and chassis dive under braking. Fourth, the springs determine how the load on the tires shifts during braking, cornering, and acceleration. This makes them a pivotal component in establishing the neutral handling balance of the car. And finally, the springs are the major factor in establishing the ride height (ground clearance) of the chassis. The series of compromises needed to create the ideal setup for a given car and performance application require experience, engineering, and testing.

Sport springs should lower the car which also lowers the center of gravity and improves handling performance. But if the springs are not stiff enough at the lower ground clearance, the chassis or suspension will bottom, causing damage to the chassis or suspension. If the springs are too stiff, the ride is horrible and tire contact patch control over bumps deteriorates. For a competition situation, ride comfort is not an issue, but controlling the tire contact patch over bumps is a major concern. Bumpy surfaces require softer springs than smooth surfaces. This compromise is critical.

Q: Standard to Metric conversions:

Q: Why didn't I get the amount of drop I was supposed to?
A: The amount of drop listed for our applications is an average. There are so many different variations in models (2 door, 4 door, hatchback, different engines, auto or manual transmission, different options, etc...) that the weight of one car compared to another varies significantly. Also, other modifications you have made can affect the weight (heavy amplifiers, subwoofers, etc...). Another factor that can affect the drop is the age of the vehicle. Older vehicles may have settled over the years, so that you realize less drop than you would if the vehicle were new.

Q: Why do bushing brackets sometimes break?
A: Typically the bushing brackets will only break when they have not been tightened down securely after installation. This will allow the bracket to move against the bolts and eventually it will fatigue the metal and snap off completely.

Q: Why do you only make a rear sway bar for my FWD car?
A: There are some applications that only need a bigger rear sway bar to neutralize the vehicle's body roll and enhance the vehicle's handling to optimum levels. Adding a bigger front sway bar into the mix isn't always necessary and in some cases it will bring back the unwanted under-steer.

Q: Will my springs "settle down" (wear in or drop a little more) after a while?
A: No. Anybody that tells you "their brand" of springs need to "settle in" is really saying one of two things: 1) Their springs aren't pre-set (sometimes called blocking or pre-stressing), which, while saving the manufacturer money, gives you a less durable product and inconsistent ride height, or 2) They just want to get you off the phone. Where you might see some settling is on NEW vehicles. This happens because the rubber suspension bushings tend to settle after a period of time, NOT because the springs have settled.

Q: Will your Progress Sport Springs affect my vehicle warranty?
A: Warranty coverage often varies for each vehicle. Usually, suspension components are generally considered normal wearing parts not covered by warranties. Vehicle manufacturers are required BY FEDERAL LAW to honor your new vehicle warranty, with exceptions for modified parts and their "related components." Modified parts are NOT covered by new vehicle warranties.