What is a balanced dirt stock car?
It seemed for years all people talked about in our type of racing was the car being too loose or too tight. There was, for a long time, no talk about a balanced car. Now recently talk about balancing a car has become more popular. I recently got a good education from Darren Miller on what is his version of a balanced car; or what I should say what it takes to balance a car. Now a word of caution; I’m not saying that by working on your car to get a perfectly balanced set up will enable you to win every race every time, but a balanced car will be more consistent and not fade as much over long races than a car that isn’t balanced as well. So, that said, let’s dig in to it.
There are way too many things to adjust on a dirt car to be covered in one blog post, but I will cover what I believe to be the core group of things that most dramatically affect the balance of a dirt car or probably race cars in general. I believe the main areas to focus on are: left side weight, wedge, rear weight percentage, RF spring rate, and wheel tracking. There are many other areas of the car that do make a big difference, don’t get me wrong I do pay attention to the entire car, but these five are the ones that most affect the car.
Weight balance in a stock car
Left side weight percentage seems to be the key effect on the car. To get maximum traction off the corner both rear tires should be loaded to the maximum of their available traction. Traction is dependent on loading the tire to its maximum slip angle and slip ratio, but that is a completely different article. As the car enters the corner, weight is transferred from left to right. If left side weight is too high, not enough weight is transferred to the right and the car won’t stick and turn into the corner. It just goes into a four wheel drift up the track. If left side weight is too low the car will either be very tight or very loose into the corner, but not have the traction off the corner that it should. Another aspect of left side weight percentage that needs to be considered is that as the track dries out and slows down, weight transfer from left to right goes down because the amount of lateral G forces exerted on the car goes down. To keep the car balanced a change should be made to keep the weight balance the same left to right. Some common adjustments could be decreasing the left side percentage, lowering the roll center, or raising the center of gravity.
Wedge to help balance a car
Wedge seems to go hand in hand with the amount of left side percentage. As a car starts it’s decent into the corner, the wheels turn left and the driver lifts off the gas and the car starts to transfer weight to the right and to the front. The left rear tire looses the most weight of all the tires. Wedge is defined as the difference in weight between the left rear and right rear tire. Since the left rear tire looses the most weight it is usually the heaviest corner weight on the car. Too much wedge, the left rear tire much heavier than the right rear, and the car will be loose into and through the middle of the corner off the gas. Too little wedge and the car can be tight into, too much side bite on the right rear tire, and through the middle of the corner and loose off the corner. A slight amount of excess wedge the car will have a little snap of tightness as the car initially starts to accelerate off the corner.
The trend in dirt racing seems to be leaning toward a left side weight percentage of around 53.5 to 55 and somewhere between 75 and 125 pounds of wedge. These numbers are just averages and are very dependent on the class of car and the tires being run. I have heard of many cars running well outside of these parameters and winning. I always say, don’t pay more attention to the numbers than to what your car is telling you it needs. Remember there is no right or wrong as long as you end up in victory lane.
Good luck, till next time.