3. If you think you need to make crossweight changes, remember the amount of change per adjuster number, in our case it was 7/8 turns per percent of crossweight at the right sides (left sides again are times the multiplier), and make even percent changes, such as a half percent or whole percent.
Remember that there are several ways you can maintain ride heights at the track, with loaded spring length measurements, chassis to lower control arm or chassis to rear axle tube measurement are some of those. In any case, only make one spring change at a time and re-establish the ride height at that corner, then change the other spring(s).
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Finding The BBSS Front Spring Pre-Loading
For the teams that are running very soft front coilover springs, you will have a very difficult time moving the adjustment ring with your shocks in the car because of the high amount of pre-load on the spring. To carry the wheel load, the spring must be compressed quite a bit.
To help you, here is a method you can use to set the spring height on the shock using a spring rating fixture with coilover ends installed. Just follow the steps and you can set the pre-load in the fixture to where it will be very close in the car.
1. The shock length as it is installed in the car at ride height. Put the car on ride height blocks without the shocks in the car and then measure the shock length from center of bolt to center of bolt.
2. Wheel Load-We have already determined the wheel load we desire in No. 1 of the section on "Adjusting The Corner Weights," and that is 685.
3. Motion Ratio of the lower control arm. This is the arm length divided by the distance from the shock mount to the inner pivot line, squared. For a car with a 17.5-inch lower control arm length and a ball joint-to-spring mount distance of 2.5 inches, you divide 17.5 by 15 (17.5-2.5) to get 1.1667 and then multiply that by itself to get 1.3611.
4. Shock Angle-measure the angle of the shock installed and at ride height. In our example it is 18 degrees. Take the cosine of that angle, divide it into 1.0 and then square it, or multiply it by itself. The cosine of 18 degrees is 0.95106, and that into 1.0 is 1.05146. Doing the multiplication to square that number, we get 1.1056.
5. Multiply the wheel load of 685 times the motion ratio squared, 1.3611 times the shock angle cosine squared of 1.1056 and we get 1,030.8 pounds of spring preload. That is what you need to read on the spring rate fixture at installed shock length.
Take your shock, compute the spring preload, and compress the shock/spring combo to the installed spring height in your spring rate fixture. You should read the spring preload amount. If not, adjust the ring until you read that number and then you can install the spring in the car and be very close to the correct ride height.