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Weight Distribution and Cross Weight

Weight distribution and cross weight (a.k.a. preload, bite, etc.) are helpful tools for tuning your suspension. Sadly, many racers misunderstand these properties. The following kitchen science example demonstrates how chassis weights and preload work.

Imagine that you take your kitchen table and place a bathroom scale under each leg. Now, stand exactly in the center of the kitchen table. If you are exactly in the center of the table, then all four scales will register the same weight.

Now, take half a step to the left. The left side scales will now show more weight than the right side scales. In this example the weight is distributed to the left. This is obvious because of your position on the table. But it is also evident from reading the scales.

From this position, move forward one half step. The left front scale will now register the most weight. This is logical due to your position on the table. Again, by reading the scales it's also possible to tell where you are standing on the table.

Just like positioning your weight on the table, your race car's weight will respond exactly the same. However, reading the scales to determine the weight location within the car is a little more complex than this kitchen table example.

Up to this point, all four table legs have been rigid. Suppose now that you were to place a spring under each table leg. And, just to make it a little more fun, suppose the bottom of each leg had a threaded collar resting on the top of the spring.

In essence, the table now has weight jacks just like the race car. Next imagine we place the scales under the springs. If all four springs were exactly identical and the threaded collars were adjusted to be the same height, and you stand in the middle of the table, then the scales would read no differently than prior to adding the springs (except for the additional weight of the springs and collars).

However, if you were to adjust the right front spring collar to slightly compress (preload) this spring, then the right front scale will register more weight. At the same time, the left rear scale will register slightly more weight. In this condition, the right rear and left front scales will register less weight, too.

In this example, if you were to add the weights registered by the left side scales you would find they were 50% of the total. Even though the weight at each corner changed in this example, the weight distribution remained unchanged because you are still standing in the middle of the table.

About this time, many racers give up on trying to understand weight distribution and cross weight. Fortunately, the Computerized Chassis Weights software keeps things simple by providing the important end results of many complex relationships.

So far, our modified kitchen table has responded exactly the same way your race car would respond for these same changes. In reality, your race car has suspension parts (A frames etc.) making it slightly more complicated, but, the physics is the same for both the racy kitchen table and your car.

With no preload, the weight distribution is clearly understood just by reading the scales. With uniform weight distribution the prelaod can also be understood by simply reading the scales. But, throw in a mix of preload (cross weight) and non uniform weight distribution and you have scale readings that are no longer clear indications of these kitchen table examples.

Simply adding the scaled weights from diagonal corners of the car tells you little about the race car. By the time you factor in different spring rates, sway bar rates and motion ratio, different spring locations, different wheel offsets and rear axle offset, the cross weight is not much more than Voo Doo. Preload, however, is a real and scientific aspect of your race car.

Preload is also a good diagnostic tool for selecting springs on short track cars. This is where the Computerized Chassis Weights software is a major help in tuning your chassis.

When reviewing your Computerized Chassis Weights software, if you find a preload greater than 40 to 50 pounds, then you could benefit from a spring change. Some people have found preload in excess of 300 pounds.

If the software shows excessive preload in the right front and left rear, then you should interpret this as the car needing a larger front sway bar. If your car does not have a sway bar, without this software you would never know whether you could benefit from a sway bar (even on dirt tracks).

Another benefit from using the Computerized Chassis Weights software is if you find excessive preload in the right rear and left front corners. In this situation your race car could be improved by using stiffer rear springs.

Historically, advantages in racing were hard to find. Now, you can find advantages in preload by simple using the Computerized Chassis Weights.

Hundreds have been sold! So, it's very likely the winners at your track already have this advantage. Don't miss yours! Order today and get the full benefit from weight distribution, preload, and more!

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