Ok, here you go. You bought a race car or built one yourself, now what? Before you start slinging dirt or peeling rubber off your tires you MUST put your car on some type of scale, to accurately place your weight of the car to where it will effectively work while you race. This chapter is a basis to start. Once you scale your car and get a system down you will be able to complete scale time at a minimal effort.
Scope:
A Race car is placed on a set of scales to precisely measure corner weights, left side weight, rear weight and cross weight. All of these different weights have a major impact on race car handling. Corner weight is how much weight is transferred through the suspension to each tire. Left side weight is the combined weight of the left front and left rear tires. Rear weight is the combined weight of the back tires. Cross weight is the combined weight on the left rear tire and the right front tire, this is one of the most important areas of setting your car up for racing.
Fundamentals of Scales:
There are several different types of scales that you can use to weigh your car. The most inexpensive type of scale is a grain scale. These scales use sliding weights on a balance bar to tell you the amount of weight that is placed on it. This basic scale is enough to get you close to the set up that you will need you will need to calculate your final percentages with this type of scale. The second type of scale is called a Bathroom scale, these scales are nothing more than a bathroom scale that is set up on a cantilever frame that reduces the weights to the bathroom scale by at least half. These are the hardest scales to use, only after you calculate the weight that is on them can you actually tell what you have, and you also have to calculate your percentages. Depending upon the brand you buy they are less reliable. With both of the above scales you have to calculate your left side weight, rear weight percentage and cross weight. Modern electric scales are very easy to use and most all of the modern scales are capable of telling you your weight percentages, these scales are also very accurate. This is your best solution for setting up your race car.
Things to do when setting up your scales:
Everything mentioned here is a must when it comes to weighing in your car.
Find a spot in your garage or outside that is level. If its not level make it so. Once the scale area is level mark these spots for future use. You will have to scale in the exact spot every time you place your car on the scales for it to be effective. once you have level ground place your scales on these spots and mark around the scale to set the spot for future use. I always use a water level to ensure that all the scales are level. It is very difficult to find a straight edge that you can use in between the scales each time, so the water level is the quickest and easiest leveling device. If you are working in an area where you can run strings across each direction over the center of the scales you can use a level and run the strings. Measure the distance between the string and the top of the scale, Level the scales according to the dimensions you take. Once the leveling is complete you can focus your attention on your car.
Follow the same procedures for scaling you car every time you do it........:
""Very Important""" The only weight that you will be able to move without physically moving anything in the car will be the cross weight. To change the left weight or rear weight you will need to physically move something around on the chassis. I.E. weight or battery.
Rules of Scaling your car:
When scaling your car first do the following:
Make sure you have the amount of fuel in your fuel cell that you are going to race with. Most chassis manufacturers have a rule of thumb for how much fuel is in the fuel cell when on the scales.
Make sure all your fluids are topped off. Fill the radiator that overflowed the week before, change your oil before you scale the car. fill your rear end and transmission with the proper fluids.
As you scale the car you must constantly check the air pressure of all your tires on the car. Racing tires and rims go flat over time and the amount of time it properly takes to scale a car can let a tire go flat and you will not have the proper numbers at the end of your session.
Unhook the top of all shocks and place as to not interfere with the suspension movement while on the scales.
Place a string line from the front tires to the back tires, use this string to measure your ride heights that your manufacturer recommends. It is always good to keep stringent records of your setups to look back on and also incase the car gets bent. You will notice something is wrong when you adjust your cars heights and the weight is not there.
Locate your axles to the chassis
Set your ride heights after your tire pressure is set. As you adjust your ride height by corner go back and check all other corners, you will notice a change in all the heights as you make adjustments. This is the most time consuming procedure of scaling your car.
Set your panhard bar length and angle
Set your pull bar length and height
Set your pinion angle.
When you are ready to check your weight percentages you must always bounce the suspension to make sure the weight is not hanging up on a corner. Push down on the front and rear bumper and pull up on the bumper to work the suspension, let it settle and you are ready to check your weights.
Once you get your weight the way you want it set your toe out Remember the more toe out you have the more stable the car will be down the straight aways. Rule of thumb is to go from 1/8" for long tracks to 1/4" for short tracks, the more toe out you run the slower your car will go due to tire scrub. The friction on the tires is greater as the toe is increased.
Check and adjust your caster and camber
If adjustments are needed to adjust your cross weight remember that putting a turn on the left rear tire and a turn on the right front, while removing a turn from the left front and a turn off the right rear will increase cross weight. To remove cross weight take a turn off the left rear and right front tire and add a turn to the left front and right rear. Keep taking turns off or putting turns on the same on all corners of the chassis.
Once you are finished with setting toe, ride heights, caster and camber and locating your front and rear axle, make sure you read the weights one more time. To make sure that nothing has changed on you.
Hints:
If your left side weight is to much. Try moving something to the right side of the car. Change your wheel offsets on the car, if you have a lot of left weight you can extend the left side tires away from the car and move the right side tires toward the car to lessen the left side weight and vise versa for not enough left weight.
To much rear weight? Think about removing weight from the rear or remove racing fuel from the fuel cell.
Racing Fuel weighs 6.2 lbs per gallon.
Tire pressure can alter weight of the corners and cross weight. Experiment with it on the scales log down all your information with different combinations and you can use them on the track if your car is to tight or to loose.
Remember::Racing is a dangerous sport, Always practice safety in and around your race car.
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