That is your servo Saver. The tighter that is, the easier it is for you to damage the servo, when you crash, but you will have more responsive handling. Too Loose and you will lose response. Or even worse, it’ll be fine at slow speeds, and then as you accelerate out of a corner the servo saver kicks in and your car goes straight without finishing the turn….boom, hits a curb.
There is a small hole in the bottom of the chassis. You need to use one of your hex wrenches to adjust it. I forget which size is correct. Search for servo Saver and you will find a better answer.