Setting the ride heights and corner weights is the very foundation of every setup. Most of
I sometimes watch in frustration as teams struggle to set the corner weights and ride heights on their cars. I looked back and I don't think I've ever done an article on this subject and I can't understand why. The process is so basic to the setup of the car. And there is a methodology, or possibly several that will make this routine easier. Let's explore some ways to do this in an orderly and sensible way.
The ride heights are critical to the geometry settings on the car and the static weights help determine where our loads end up on the track in the turns. Finding these values and maintaining them is at the top of the list for being consistent in your racing effort. Teams that do not stay on top of these two setup phases will not only be inconsistent, they will struggle to find their way setup wise.
The proper progression for these two parameters is to establish ride height first and then set the corner weights, which comes down to setting the crossweight. There is a reason for this order. Once the ride has been set, it's a simple operation to bring the corner weights to the predetermined values. So let's study ride heights first.
Why Ride Height is Important
Your ride heights determine your arm angles up front, as well as the cambers, and, to a lesser degree-excuse the pun-the caster angles. Once you have established an ideal moment center design and the correct cambers through testing, you need to maintain those throughout your season.
Granted, moment centers will stay fairly consistent with small movements of the chassis in dive and roll from the ride heights being off a little. That is because all of the points move together. If you moved only one point, then the problems begin. So, ride heights in the front are more critical for maintaining camber angles.
There are legal issues too at the front. No, not as in the law, but in being legal in tech. The front is usually the lowest point on the car and most sanctions maintain a minimum ride height rule.
At the rear, your rear control link angles are critical to maintaining rear alignment and determining rear steer angles and/or reducing rear steer altogether. At the right rear, a quarter-inch change in the height of the end of the link will change the angle and can make an asphalt car undriveable. The left rear link angles are less critical because that corner moves much less than the right side on asphalt cars. On dirt cars, both rear corners can move quite a bit, so the link angles on both sides are important.
Establishing Ride Heights
Now that we understand the value in maintaining ride heights, just what heights do we want? First off, you must maintain the legal ride height to pass tech. Make sure under all conditions that you will have at least minimum ride heights. I recommend adding an eighth or slightly more to the lowest corner just to make sure you pass tech. Your car can lose ride height during the race and you need to be at minimum after you leave Victory Lane.
Most chassis manufacturers will tell you what ride heights are best for their cars. The car is built on a jig for a particular ride height layout. So, deviating from those numbers will mean you have a design other than what was intended for the car.
Some racers like to take matters into their own hands-and that's OK. Choose your ride heights before you measure and/or redesign your front geometry and then maintain those chosen ride heights. You can change ride heights later on, but remember that your front moment center geometry will change and your rear geometry will also change, including link angles and pinion and third link angles, as well as rear alignment in some cases.
The ring adjuster on a coilover shock is what is used to set ride height and corner weight
This is a very good example of a stock class spring adjuster. We count the number of turns
Even in stock classes where jack screws are not allowed, we can use adjusters and still be
Now that we understand why we need to maintain a set ride height, let's go through an example of how to set ride height. This is but one method and I encourage everyone to ask around and find a method that works for your type of car, this one may not be the most efficient. Do not copy these ride heights; they are only used as an example. Your car may be designed to run different ride heights than these.
1. Determine your ride heights. Ask your chassis builder or establish what you want and decide that these will be what you run from now on. For our example, we use LF 4.00, RF 4.50, LR 4.50, RR 5.00.
2. Choose a level spot in your setup area. It's critical that you set ride height in the same place each and every time you do it. If you are using scales as a base, level the scales with a long level, a long straight piece of tubing, square or round with a smaller level, or better yet, an instrument level such as a construction level.
3.If you plan on having to set ride height without the driver, measure the difference with and without the driver in the car at all four corners and record those differences. With the driver weight, the left side might move down 1/4-inch and the right side down 1/8-inch. Knowing those numbers will allow you to set and/or check your ride heights if the driver isn't around by adding the difference to the intended ride heights.
4. Prepare the car. Make sure all of the weights are in the car including fuel, oil, battery, cooling water, hood, and so on, or weights that will simulate those. The driver is optional based on No. 3.
5. Air up the tires as they will roll through tech. Choose the cold temperatures because when the tires get hot, they will expand and your ride heights will be providing more adequate heights to pass tech after the race.
6. Disconnect the sway bar. We will deal with preload on the bar later on. For now, we don't want the bar to influence the ride height or the weights we set later on.
7. Calculate the average front and rear desired ride heights. In our example, the front average is 4.25 and the rear is 4.75.
8 Read the ride heights as they exist. Record these. For our example we have LF 3.625, RF 4.75, LR 4.625, RR 5.75.
9. Calculate the average existing ride heights front and rear. We have 4.1875 front and 5.1875 rear.
10. Find the difference from the desired average ride heights. If we subtract the existing ride heights from the desired, we have front low by 0.0625-inch and the rear high by 0.4375-inch.
11. Adjust the front up by 0.0625-inch and the rear down by 0.4375-inch. Do this by making equal changes to the adjusters on each side. At the front, we will move the LF and RF adjusters up by 0.0625-inch.
12. Adjust the rear down by using the same method as in No. 11. In our example, move the LR and RR corners down by 0.4375-inch.
13. Now that we have the front-to-rear rake set, we adjust the side-to-side rake. The new existing ride heights are LF 3.6875, RF 4.8125, LR 4.1875, RR 5.3125. The LF needs to go up 0.3125 and the RF needs to go down the same amount. So we turn the RF adjuster up (to lower that corner) 2.5 turns and the LF down (to raise that corner) 2.5 turns.
14. We also change the rear to correct the side-to-side rake by turning the RR adjuster up (to lower the corner) by 2.5 turns and the LR adjuster down (to raise that corner) by 2.5 turns. Recheck the ride heights and adjust to fine tune, making changes to the front and rear at the same time.
Once we have established our ride heights and weights at the shop on a level surface, we c
Another method of recording the ride height for reference is to measure from a point at th
Changes in ride height have an effect on the front geometry and the rear as well. In the r
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 grain scales to find your wheel weights. Just make sure when you
Click image to enlarge.
Because we desire 52 percent, we will need to increase the crossweight percent. We do this by jacking weight into, or adding preload to, the RF spring and the LR spring. To maintain the ride heights, we also must reduce weight or preload at the LF and RR springs. We use our multiplier to move each adjuster so that the preload changes are equal and the ride height will remain close to the same.
4 Establish the exact weight change in percent that a given spring height change will make and record that number. To do this, we add five rounds of pre-load to the RF. We also take five rounds times the multiplier for the front of 1.25 × 5 = 6.25 rounds out of the LF. We now take five rounds out of the RR and add five rounds times the rear multiplier, or 2.0 × 5 = 10 rounds to the LR. The crossweight percent will have changed to, say 55.4 percent.
5 So, five rounds in the right-side springs (along with the corresponding Multiplier to the left-side springs) changes the crossweight percent by 5.6 percent, which is 1.12 percent per round, or 0.89 rounds per percent of crossweight. That is equal to 7/8 turn of the adjuster. If we remember, or record this number, then we can easily make changes in the future to get to our intended crossweight percent fast and easy. For our example, we need to go from 49.8 to 54 percent.
So we multiply the difference, or 4.2 percent, by 1.12 and we get 4.7 rounds of right side change to the spring pre-load, or 43/4 rounds. The left side changes, of course, will be 4.75 times the multiplier for front or rear. We should now be at, or near, the desired crossweight percent.
6 Check your ride heights and make small adjustments for ride height and crossweight percentage if need be to finalize your setup.
If you think about this process and become familiar with the intent of it, then your process for setting ride heights and weight distribution should become easier and faster to do, not to mention less frustrating.
Carrying Ride Heights to the Track
Now that the car has the correct ride heights and weight distribution for your setup, you need to make sure those don't change at the track. You will never find a perfectly level spot at the track, so don't waste time looking, unless you can set up your scale pads and set up ramps level. But this is almost never the case.
And don't ever believe the track scales. They are never level. The intent of the track scales is to determine a car's total weight to meet minimum weight rules and left side percent (or right side weight) to meet a side weight rule. Crossweight is of no concern to the track officials. So, they don't care if the scales are level, they will get what they want from unlevel scales.
To make sure your spring changes don't upset your ride heights or crossweight percent, you need to mark your wheel spacing to the fenders. Here is what you do.
1. Find a fairly level spot and mark on the ground with duct tape or marker where the tires sit on the ground. Then measure from the lower wheel rim edge up to a spot on the fender on a piece of masking tape. I usually mark an even inch and write that inch number on the tape. Do this at every wheel.
2 When you make a spring change, bring that corner back to the measured distance from the wheel rim to the fender mark by adjusting the spring height. Do not adjust any other wheel's spacing. Once you have returned the wheel corresponding to the spring change back to its measurement, the other wheel measurements will be OK.
For the teams that run very soft front springs, adjusting for ride height and wheel weight
Once you have set your ride heights and weights, it's a good idea to tape the adjuster rin
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).
Click image to enlarge
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.