12. Measure the new, compressed shock length. Subtract the new shock length from the original static shock length and divide that number by the shock motion ratio we found in step No. 8 to find how much the wheel moved (wheel movement) and record that number.

13. Divide the sprung weight of the RF corner by the amount the wheel moved to find the Sway Bar Wheel Rate. Example: If our RF sprung weight were 600 pounds and our wheel moved 1.0 inch, then the sway bar wheel rate would be 600 pounds/inch.

**Finding The Bar Rate** We now have the wheel rate of the bar. This is not the last step in the process. We need to know the bar rate at the end of the sway bar arm. Here is how we do that.

1. Measure the length of the lower control arm. This is the right angle distance between the center of the lower ball joint to a line drawn between the two chassis points, or pivots, for the lower arm. This is known as the rotational radius.

2. Measure the distance, parallel to the rotational radius, from the center of the lower ball joint to the center of the point that attaches the sway bar arm to the right lower control arm. If it is a Heim joint, measure to the center of that.

3. Subtract step No. 2 from No. 1 and divide by No. 1. This is the sway bar motion ratio. Example: The lower control arm rotational radius is 19.0 inches and the BJ to sway bar mount distance is 3.0 inches, so the sway bar motion ratio is (19.0 - 3.0)/19.0 = 0.84211.

4. To find the sway bar rate at the end of the arm, we divide the sway bar wheel rate by the sway bar motion ratio squared (step No. 3 times No. 3). Example: If we have a sway bar wheel rate of 600 pounds/inch and a sway bar motion ratio of 0.84211 (this number squared is 0.70914), we calculate the sway bar rate at the end of the arm to be (600/0.70914) = 846 pounds/inch.

**What This Tells us** Once we find the bar rate, we can relate that to our setup. In our case, we found that the arms were bending excessively affecting our bar rate. A 1.75-inch diameter thick wall bar that should have rated around 1,900 pounds/inch or so was only rating just over 900 pounds/inch because the arms were bending so much. The larger the bar we installed, the less the rate went up because the arms were bending more by taking more load. The bars were doing less work.

The arms became a spring with a much lower rate than the bar. When we combine two springs in series, that affects the overall rate and in this case with the much lower rate of the arm, we recorded a lower bar rate. This could be happening to your car. In our case, we need to change to a stiffer arm in order to get the full benefit of the larger sway bar.

Accuracy Versus Results In any routine, we can only expect the results to be as accurate as the effort we put into making sure all of the steps are done correctly and that no other influence affects the results.

The maintenance of the ride heights is important because when the chassis rolls, the center of gravity moves and there is load transfer taking place. This skews the results of our test and gives us false numbers.

Make sure you zero your scales before taking any readings and lock the steering shaft so the wheels don't turn. This could affect the results. Also take your measurements a couple of times to make sure you read the tape correctly. Take your time in all phases of the test and think out the process to maintain accuracy.

**Conclusion** What you find for rates in your sway bars might be what you expected or not. This is why we go through this type of exercise. We need to know every influence that affects our setups. In the case of the Grand Am car, we found that the rear sway bar was very soft with the components that were used, and so we stiffened it and the result was a much more balanced car.

You can go to our website and under the heading, "Multimedia" you will find calculators that include a sway/torsion bar calculator. Using that, you can quickly find what your bar should rate and compare those numbers to your test results. The coefficient of elasticity, or the stiffness of the steel factor, used in the calculator is the average for hardened steel. Your bar stiffness factor may vary from that either higher or lower. NASCAR-style three-piece bars tend to be stiffer and stock-type one-piece bars tend to be softer.

In any case, you now know how hard your sway bar is working and you can make some decisions about how large a bar to use or if you need to re-evaluate the arms you are using. Information is the key to being able to properly plan out your overall setup.

Mark prepares our car for testing the true rate of the sway bars at both the wheel and at the end of the arms. This method is both easy to do and very effective and accurate. The results might just surprise you.

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