Putting your dirt late model on scales
I need to preface this post by saying that I don’t believe to have a fast dirt lat model that we need to live and die by scaling numbers. Scaling numbers are a good reference point; they are something to compare notes on handling with someone else with the same car, the same motor, racing at the same track, and having the same driving style. Scaling numbers set a good base line to work from when you have made changes in other areas of your car so that at least the scaling numbers remain consistent. I don’t believe that setting your car on scales is going to, at least most of the time; reveal the whole answer to the speed of your can. Basically, I believe too many people put too much emphasis on scaling. If I was done with all of the maintenance on a car, and had four hours left to do the something else to try and make the car faster, I would spend three hours modeling different parts of the car in a dynamic state, to see if I could learn something on how the car works, and one hour on scales tuning in that ideal wedge.
You can definitely use the scales in your modeling process to see what changes in springs or bar changes do wedge, but keep in mind that scales talk to us in a static state. We need to understand suspension in a dynamic state to really know what is happening to our cars. Scales are a very useful tool, but too much emphasis on one thing can slow you down. So with that being said, let’s get on with the main topic. Scaling and dynamic set up of a dirt car.
The first thing I need to mention is about repeatability. When we set a car on scales we are essentially measuring only a few key items: left side weight, rear weight percentage, total weight, and wedge. I am a firm believer then in keeping some essential factors very static scaling after scaling. Those factors being tires, scale placement and weight of the car. A set of old tires that won’t get raced anymore make an excellent set of scaling tires. Write the correct amount of air pressure to set them at right on the wheel and save those tires only for scaling. Scale placement is another factor I like to keep consistent. I don’t know too many dirt racers with surface plates in their garage. So pick out an area in the shop that can be a convenient place to scale and mark this on the floor so the four scale pads sit in the same position every time. At some point you have to make a decision whether you are going to scale with or without the driver. Because I help out many different people and I need a way to reference all the different cars the same, I always scale with a driver. If I were to work only on one car, I would probably scale without the driver just because it will be much easier. Since I am a kind of a ‘give a car what it wants’ type of tuner, the scale numbers would be for my reference only. I might still put the driver in the seat once in a while to keep an eye on the change in weight, but as a tuning frame of reference I don’t believe it is necessary.
The scaling basics
So the first thing you want to do is set up the car with your scale tires set to air pressures, set your fuel level to what you like to start with, and sit your driver in the seat, if you choose to go that direction. The next thing is to set up your left side, your rear, and your total weight percentages. Unless your ride heights are way out of whack, turning on the jack screws will not affect these percentages. The next thing is to set ride height and at the same time keep an eye on your wedge. You don’t want to get the wedge too far off as you are setting ride height. Each chassis manufacturer sets ride height in a different location. On most dirt cars ride height is most critical on the right rear and both fronts. The left rear is usually left to vary with the amount of wedge. I think on of the most accurate ways to set the ride heights are off of shock height. It is usually the most consistent because it is the closest to the center of the tire. The hard part is accurately measuring it. I like to scale cars up on scaling pads to get the car far enough off the ground so you can slide under and measure things from the bottom. Be very careful when doing this, I have heard of many people getting hurt or killed when their dirt late model falls off the pads and lands on them. I’ve heard of many ideas to keep this from happening from chalking the wheels to putting the car in gear, but the best one I heard about is making a rod to depress the brake pedal and hold the brakes on during scaling. Whatever method you choose, please be careful.
Front end settings
After ride height is set the next thing is to set your caster, camber, and toe in the front end. If these are way off they can affect the wedge, so it is best to set these before you set wedge. If you have one of those sweep style caster camber gauges, there should be instructions on the back on how to use it. The one I use is made by Longacre. Attach it to the spindle snout and, with the wheel parallel to the center line of the car read the camber. Next turn the wheels twenty degrees, so the front of the wheel is pointing out. Reset the bubble on the gauge so it is at zero, then turn the tire so the front of the wheel is pointing in twenty degrees. You can either use turn plates to determine what is twenty degrees, or there are angles cut into the corners of the gauge that are twenty degrees. You only need to figure this out once. Just record the steering wheel position of a twenty degree angle is, from then on just turn the steering wheel that same amount. On most late models I deal with it is around a half turn. The next part of the front end is setting toe. Some people use toe plates on the side wall, some like to run a line down the center of the tire, the best way I’ve seen is to put a piece of tape with an “X” on it on the center of the tread of the tire in the front. Take a measurement, then rotate the tire to the back, 180 degrees from where it was and take another measurement. The type of car and the space restrictions make a big difference in the method you choose. Now it is time to set the wedge in the car.
Dialing in the wedge
If you kept your wedge close when setting ride height it shouldn’t be too difficult to dial it in. My rule of thumb is for every two turns you go in the back of the car you need to go one half in the front. This is what I use for late models so the ratio may be a little different for other types of cars. If you need to increase wedge you put turns in your left rear and right front and take out the same amount of turns from the right rear and left front, using the front to rear ratio I mentioned above.
After the wedge is set, record all of your settings for reference, set your bump steer. This is quite a detailed procedure so I will handle that topic in a future article. Last thing I would do is recheck your toe setting and pull the car off of scales. Done. Everyone has their own procedure they like to follow. Every one of them is a little different.
Til next time, happy scaling.