Before anyone gets confused with this steering business, it is important to define understeer and oversteer. We could go into the technical definitions getting into slip angles of the tires or accelerations of the front end compared to the rear. That seems over the top. When cornering, every driver has pushed his car past the limits of adhesion. It is understeer if he turns his front wheels, nothing happens and he hits a wall. Oversteer happens when he turns his front wheels and the back end swaps ends with the front, and hits the wall going backwards. For all you NASCAR fans out there, when a driver says the car is "pushing" or "tight" then he is referring to understeer. On the opposite end, it may be "loose" and oversteering.
Enough of that. There are many things to influence a car pushing or being loose, including the driver. If you have any more questions or are still confused, I am going to refer you to my friend Google.
During data analysis last time, the car appeared to be understeering through the corner exit. There are several strategies to determine the cause. First, data reveals if it is the car's fault, or the driver's fault. A quick look at the steering plot, and throttle channel can show this. During a car's transient maneuver, it can only change directions in a finite amount of time. The driver may turn the wheel very fast, yet the car cannot respond that quickly. To find how fast a driver can turn the wheel, take a similar speed and radius corner where the car was neutral handling. Last, take the derivative of wheel position with respect to time, and out comes a speed. Comparing the two will reveal how well the driver is trying to make the car corner. So if the velocities are in the same ballpark, its not the driver...not quite! The last phenomenon is power on understeer, or the driver hitting the gas pedal too early and not spinning the rear tires, pushing the front beyond its limit of adhesion. Sometimes a simple driver technique correction will fix the problem. Other times the differential is at fault. Since differentials are notoriously hard to tune without separate wheel-speed sensors, I will leave it to someone else to explain how this is done.
If all of these parameters are ok, then it is most likely the car setup causing this condition. Going back to the data, there is a small amount of understeer in every corner so an adjustment should be made. Several systems on the car can be used to tune this depending on the conditions. Since this is the current example: I used dampers to correct the problem. It only occurs on corner exit, a transient condition, as opposed to steady state. Put a few clicks of stiffness into the rear low speed bump, and done! problem solved.
As a disclaimer for everyone out there who are shouting "Hey you are taking grip away from the rear, you should always add grip to the the offending side to find a balance."
This is not always the preferred method, and there were other factors that went into my decision.
This is the end of any posts on how to correct vehicle dynamics problems, since it could go on for days. But it is a sample of what data analysis needs to be done for every corner between sessions to decide on the next setup. Unfortunately cars don't just understeer and oversteer, due to the examples listed above and many factors must be considered during every data analysis session.
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