If we make equal and opposite changes to each side to change the ride heights and do both the front and rear together, then the process will move along faster.
Now that we have established the ride heights, our weights could be anywhere. Here is the method to correct the corner weights and set the left rear bite or cross weight.
Adjusting The Corner Weights
Adjusting the corner weights is how we establish the crossweight percent, or what is often referred to as the amount of bite, left rear weight, or wedge. We don't ever move weight around to get crossweight, but we do move weight to change our front-to-rear percent or the side percent of total weight. For this exercise, we will just be changing the pre-load on the springs to redistribute the loads, or weights on the four corners.
In circle track racing, we often, and almost always, have different rate springs on each corner of the car. Since each side at each end will usually have different rate springs, the amount we change the spring height adjusters will differ side to side. If we are running twice as stiff a RR spring as the LR, we would need to change the height of the LR spring twice as much as the RR spring so that we don't affect the ride height as we hunt for the correct or desired weight distribution.
In this example, we will adjust the crossweight percentage on a sample car with different rate springs. Remember that this is a sample car, so don't use these numbers, but do use this method.
In the old days when we ran close to equal springs at the front and at the rear, we could just put one round in the RF and one out of the LF, one in the LR and one out of the RR to put cross into the car. That method keeps the ride heights close to the same. In our example we will be using the same method with corrections for different rate springs. So, we are not reinventing the wheel here, just refining the process.
1 Establish the corner weights you think you need for your car. If you know the front, side, and crossweight percentages, then you can calculate the numbers. Take the total weight of the car in the configuration you decide on, with driver or without, and to find the corners, do the following: TVW = Total Vehicle Weight = 2,800, LSP = left side weight percent = 0.54, FWP = front weight percent = 0.51, CWP = Crossweight percent = 0.52.
A. To find RF weight:
TVW × CWP × FWP or, 2,800 × 0.52 × 0.51 = 685
B. To find LF weight:
(TVW × FWP) - RF = 743
C. To find LR weight:
(TVW × LSP) - LF = 769
D. To find RR weight:
TVW - (RF + LF + LR) = 603
2. Calculate the spring rate multiples. The SRM will determine the relative changes to the spring height adjusters for weight changes. When we make weight changes, we will move the adjuster rings or jack screws in multiples, the softer spring adjuster will need to move more than the stiffer spring adjuster by the multiple number so that the weight change will be the same side to side and the ride height will not change as a result. (i.e., if we move the RF adjuster two rounds, then we will move the LF adjuster 2.5 rounds.) Here's how we find the multipliers.
A. Record each spring rate.
B. For our example we use: LF 200, RF 250 - 250 ÷ 200 = 1.25 multiplier for the front.
LR 175, RR 350 - 350 ÷ 175 = 2.00 multiplier for the rear.
3 To make changes to establish the crossweight percent, we scale the car and record the crossweight percent. Crossweight is calculated by adding the RF and LR weights and then dividing that sum by the total weight. Example: RF = 643, LR = 751, so, (643 + 751) ÷ 2,800 = 0.498, or 49.8 percent.
It is perfectly OK to use...
It is perfectly OK to use grain scales to find your wheel weights. Just make sure when you roll them into place that the tops are level to each other. You might need to space under the tires to attain a level plane under the tire contact patches. And mark the location on the floor where you will place the scales each time.
Click image to enlarge.