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CTP TECH CENTER
Once the race car is well balanced and the shocks are doing their job, it is critical to evaluate brake bias for proper turn entry. Proper brake bias won’t fix an ill handing race car but is essential to maintaining a neutral handling car when the brakes are in use. The influence of your brake bias can be determined by entering the corner with light braking and entering the corner with heavy brake use to see if there is a difference. If there is, try to adjust the brake bias to eliminate the adverse handling. It is helpful to install a set of Brake Balance Gauges so that you have real numbers to determine front to rear bias. If your braking system has a balance bar, the use of a Brake Balance Adjuster allows you to make significant changes in a limited number of minutes or laps. Practice time is critical and expensive. Make the best use of the time provided!
Many people believe that springs and shocks make up the heart of the suspension system. If this is true, then you better have the right pieces or victories will be very hard to find! Spring rate is the amount of weight or force that is necessary to compress a spring one inch. If the spring is “linear” it means that if it takes 250 pounds to compress the spring one inch, you will need another 250 pounds to compress it another inch. Another 250 pounds of force will compress the spring a third inch. As you have 750 pounds to compress the spring 3 inches, the spring rate remains 250 pounds.
Spring rate is determined by three factors:
- The diameter of the wire used to construct the spring. The larger the diameter of the wire, the higher the spring rate
- The larger the diameter of the spring, the lower the final spring rate will be, when the same size wire is used.
- The final factor in the spring rate is the spacing (or pitch) between the coils, or the number of coils that make up the spring. The higher the number of coils, the lower the spring rate.
Knowing the actual spring rate of each spring is critical. Even though automated equipment is used in spring manufacturing, spring wire is not consistent. Due to this inconsistency, not all springs will come out exact.
Other things that can alter the spring rate include:
- Heavy or extended use which can lead to collapsing.
- Damage from impact with the wall or another competitor
Camber is the tilt of the tire as viewed from the front of the car. If the top of the tires lean toward the center of the car then you have negative camber. If the top of the tire tilts out away from the center of the car then you have positive camber. Adjusting camber can have a dramatic effect on the cornering of your car. Most oval track racers run negative camber on the right side of the car and positive camber on the left. Optimum camber settings will result in more speed and ideal tire wear. Camber is measured with a caster camber gauge and is usually easily adjusted with shims or adjustable upper a-arms. Always check the toe when making camber or caster adjustments. The amount of static camber that you should run is a result of testing, pyrometer measurements, front suspension geometry and discussions with your car builder. Remember that poor camber settings will cause excessive tire wear. Camber settings set to extremes can reduce the braking ability of the car.
To understand caster you need to picture an imaginary line that runs from through the upper ball joint and extends through the lower ball joint. From the side view the imaginary line will tilt forward or backward. The tilting of this imaginary line is defined as caster. Caster is measured in degrees by using a caster camber gauge. If the imaginary line described above tilts towards the back of the car, at the top, then you will have positive caster. If the imaginary line tilts forward then you would have negative caster. Positive caster provides the directional stability in your racecar. Too much positive caster will make the steering effort difficult. Power steering will allow you to run more positive caster. Negative caster requires less steering effort but can cause the car to wander down the straightaway. For oval track racing most racers run more positive caster on the right side tire than on the left. The caster split helps pull the car down into the turn, helps the car turn in the center and helps it stay hooked up on exit. How much caster should you run? The amount and split depends on the type of car and track conditions. The details should be worked out with your car builder and through testing.
Caster / Camber Gauge
- Read to the center of the bubble.
- Camber uses outside vials and reads in 1/4º.
- Turn wheels 20º to R & L of center when setting caster w. vial type gauges.
- Find a level place to set up your front end.
- Attach the gauge to the spindle. If you have a magnetic adaptor be sure that the surface you attach to is machined square to the spindle and doesn't have any nicks or burrs.
BE SURE WHEELS ARE POINTED STRAIGHT AHEAD WHEN SETTING CAMBER.
With the thread-on type adaptor be certain the spindle threads are free of burrs. Usually there are a few extra threads on the spindle. If not you will need to remove the spindle nut and install the adaptor in its place.
- Rotate the gauge until the small vial at the end of the gauge shows level.
- Read the CAMBER directly on one of the two vials on either side of the gauge. Note that they are marked + and -. Read the line nearest to the center of the bubble. Each line is 1/4º.
- To read CASTER first turn the wheels 20º to the right when setting the RF and to the left when setting LF. If you don't have a set of turn plates you can use the angles machined on the corners of the gauge as a reference. Turn the wheels until the angle is parallel to the side of the car. Rotate the gauge until it is level.
- Turn the knurled nob in the center until the center caster vial reads 0º. Now turn the wheels back past center to 20º the opposite way - for a total of 40º. Rotate the gauge again to level (DON’T turn knurled knob). Read the caster directly on the center vial. Read to the center of the bubble. Each line is 1/2º.
NOTE: If you need to measure more than 12º caster - racing karts for example - turn the wheel 20º and set the enter vial at negative 4º instead of 0º. Proceed as above and add 4º to the reading. This will give you a total range of 16º.
- Adjust the caster and camber as needed. Each time you make a change bounce on the front end to settle the suspension. Remove the gauge and reinstall the spindle nut if needed.
NOTE: Adjusting the caster may have an effect on the camber and vice versa. Double check all your settings before finishing. Be sure to tighten all suspension bolts when done.
Set Toe Properly
Before you begin taking measurements you must insure that the car is race ready. Ride heights set, weight percentages correct, driver weight accounted for, bump steer set, camber and caster set, Ackerman set, air pressure set, stagger correct....you get the idea. You should also inspect the steering components and replace any that are worn or bent. Center up the steering before you begin. Center the drag link or rack so that the inner control pivots and inner tie rods are centered to each other. Tie rod lengths should be adjusted to match you lower control points if possible. Toe Plate Method: Toe plates offer fast and easy measurement of the front end alignment. When using toe plates be sure to have the toe plates resting flat on the ground and centered on the tire. You should always be sure to have the toe plates flat against the side wall. Make sure that the plate is up against the side wall evenly on both sides. Air up the tires so that there is not a bulge at the bottom of the tire in the center due to under inflation. Go the extra mile and mark the high spots of the side wall with chalk. Use a tape measure to check the back of the tire and the front between toe plates. The toe plate method should give you a smaller number at the back of the tire if you want to have toe out. Remember that any bent wheels or imperfections in the side wall will affect your settings.
Scaling A Race Car Properly
Race Ready In order to scale your car properly it must be ready to go. For the most accurate results the car must be fully prepared. If it is not "race ready" then any changes that you make will have an effect on your final setup and what you have put in your notes. So, what do you need to have done to be "race ready"?
- Fuel full
- Radiator full
- Oil tank full and motor ran or too much oil can be in the pan
- Gear oil full
- Transmission full
- Power steering full
- Lead bolted in
- Stagger set
- Tire pressure set
- Camber set
- Rear end square
"Race ready" means that the next thing the car will do is go around the racetrack. Keep in mind the changes that will be made to the weights if you attempt to scale the car before it is ready to go.
Scaling A Race Car Made Simple
Scaling your race car is arguably one the most important practices that you can do to increase your chance of visiting victory lane. Proper chassis set up requires that the weight balance is set correctly for the car, driver and track conditions. In order to achieve proper and repeatable weight balance a quality set of electronic scales will need to be obtained.
Before you begin the scaling process you should make sure that the car is race ready. Fluid levels need to be topped off, stagger & tire are pressure set, ride heights adjusted, Caster adjusted, Camber set, rear end square and the toe checked. You will also need to take advantage of the maximum left side weight and check to see if your total weight is within the rules and the front to rear balance is where you and your chassis builder want it. Emphasis should be placed on being race ready before you begin the final scaling procedure as all of these factors will have an effect on the end result.
Now that you are ready for your final scaling procedure you will need to find a level area to weigh the car. Most garage floors vary by quite a bit. Spend a few minutes with a good level and straight edge and mark four spots on the floor that you can use each time you want to scale the car. Make sure that you mark the floor to match up with your wheel base and track width.
Should the floor have low spots you can use simple shims to make all four scale pads level or utilize some leveling trays to speed up the job. Mark the shims or trays with LF, RF, LR, RR so that you can quickly repeat the process each and every week. Consistency is the goal when scaling so weighing the car in the same spot each and every week will improve your chances of having a great handling car.
Now that you have a level surface you can roll the car into position. Set the scale pads next to the appropriate tire and hook up the cables. Make sure that the cables are plugged into the correct pad and turn the scales on. Check that there is no weight on the scale pads and press the zero button. The control box should now read zero and you are ready to place the pads under the car.
Jack up one side at a time and slide the pads under the tires. Place the car in gear or use a stop to keep the car on the scales. Verify that the sway bar is disconnected or completely neutral with plenty of slop. At this point, give the rear of the car a firm settling by placing your knee on the rear bumper. Then do the same at the front.
After settling the front and rear I like to grab the roof roll bar and shake the car several times. I try to let go right in the middle. By settling the car and shaking the roof bar you are helping to insure that the shocks are not hanging up and that you have worked out any small binds in the suspension points. Try to do the settling procedure consistently as this will help you obtain repeatable results. Settle the car after each time you raise it with a jack or make an adjustment.
You can now record your wheel weights, partial weights and percentages. Check that the front to rear balance is correct and that the left side and total are where they need to be. If not then move the lead to the appropriate spot until you are happy. Readjust the ride heights if you have to move lead around.
Now you can check the cross weight. If you want to add cross weight put a turn in the right front and left rear and take a turn out of the left front and right rear. On non coil over cars you may need to go two turns on the rear for every one turn on the front. By adjusting all four corners you will help maintain your ride heights.
Now you can set the sway bar. With the car still on the scales you can see exactly how pre-load you are putting on the bar. Record your final settings and you are ready to go.
Commonly Asked Questions
- Should you weigh with the driver in or out?
You can do it either way as long as you consider the variables. Personally, I like to see the driver in the car during the set up process as he is going to be in the car when it goes around the corner. Driver weight tends to vary a bit so having the driver in the car insures the most repeatable results.
You can weigh with out the driver as long as you consider the variables that will change. As long as you factor ride height changes and the weight differential scaling with out the driver can work fine. It is really a matter of personal choice.
- How level do the scales need to be?
We get asked that a lot. For optimum results the closer to exact the better when it comes to level. Sometimes you can compromise. Picture a thick piece of flat glass with scale pads resting on top. Start with the glass perfectly level and your results will be perfect. Now take the glass and lower the front by one inch. The four scale pads are still in the same plane in relation to each other on the glass. In this scenario the effect from the front being lower will be very small. You can picture the same thing lowering the left side by one inch and still get good results.
Now picture a ½" shim on the glass under the Left Rear and Right Front corners or just under any one corner. Your scale numbers will go nuts. The shims will be shown as cross weight on the scales. The bottom line is that you need to maintain scale pads within the same plane. Raising one corner or opposing corners is going to effect your readings. In general, it is best to keep the scales as level as possible.
- Do I have to re-zero the scales if I make a change?
Longacre Computer scales allow you to make as many adjustments as needed with out re-zeroing. Simply make your adjustments, settle the car and record your results.
- Can I change the left side or rear weight by turning the jack screws?
You can turn all day and you will not move the left side or rear weight with the jack screws. To make changes to Left side or Rear percentages you will need to move lead or other mass within the car.
- Should shocks be hooked up? Yes shocks should be hooked up.
Common Problems! Here is a list of things to look for!
Wedge will change due to a variety of things that are explained below. When you notice a wedge change, have a look at the total weight. If the total is the same then odds are your scales are operating fine and there is something in the car that needs correcting. If the total changes by more than a few pounds then you could suspect a scale problem and should call the manufacturer for more direction.
- Stagger Effect
Cars that run high amounts of stagger and a locked up rear end can experience changing wedge due to the tires getting ready to "skip" like when you are push through the pits around a tight turn. Weight will momentarily be miss-applied as the tires excerpt force through the rear end gears. The axles literally climb up the ring gear causing an occasional wedge variance. To avoid stagger effect problems simply remove an axle cap and pull an axle out past the spline on the rear hub. You can even see the stagger affect on cars with differentials however it is less common.
- Chassis Binds
Sometimes A-arms can be in a bit of a bind to get the caster right. This usually happens when more shims are used on one A-arm bolt than the other. You can see wedge numbers change due to this added resistance. Try to avoid uneven shimming and be sure to keep your A-arms greased at all times.
- Ball Joints
Ball joints have a fair amount of friction and need to be greased often. The friction can cause wedge variations if the car is not settled properly. Damaged ball joints should be replaced.
- Camber Changes
When you adjust camber you are changing the tilt of the tire. Adding camber changes the wedge in the car to a small degree. Keep this in mind when recording your weights. If camber is changed, wedge will change a bit as well.
- Shock Rebound
Shocks with high amounts of rebound can artificially hold weight in a corner, especially when cold. Settling the car usually works the hydraulic fluid to get consistent readings. However, high amounts of rebound can make the weighing process harder. If possible, disconnect the shocks. On coil over type cars settle the car thoroughly.
- Tire Pressure Changes
Air pressure changes moves cross weight and will change the numbers on all four corners of the car. Be sure to have the air pressure set before you begin the weigh job. I have seen slow leaking tires or bleeders that are still bleeding cause the weigh job to be a real hassle as the wedge keeps moving every time you check it. Be sure the tires hold air before you begin.
Make sure the stagger is set. More rear stagger takes bite out of the car. Less rear stagger puts bite in the car. More front stagger puts bite in the car. Less front stagger takes bite out of the car. Make sure you do your shop set up including ride heights with the proper amount of air pressure and tire stagger.
- Camber Changes