Overdriving. It happens to everyone. In fact, it is a necessity if a driver wants to be fast. Yet in many groups and track day organizations it is a taboo topic, something that is not supposed to ever happen.
Here at Win HPDE though we are going to look at overdriving objectively, starting with why it is necessary and finishing with postmortem analysis to actually improve oneself as a driver.
To get the formalities out of the way, overdriving refers to the driver asking the car to do something the car is physically unable to do. Typically this means the car requires more grip at one or several tires than is available, resulting in those tires spinning (usually under power) or sliding (usually under braking or steering) on track surface. However, sometimes the car senses that it is about to exceed the physical grip limits and prevents the driver from exceeding said limits (such as by virtue of anti-lock brakes or traction control); in these cases the car stays within physical limits but does not honor the driver's inputs.
If overdriving is bad, why do we do it?
There is no magic way to know how much grip a car has, or how fast it can be in a particular point on the track executing a particular maneuver. Can the car brake at that 200 marker and make the turn? Is full throttle possible at this apex? Will the car stay on the track if it enters a turn 3 mph quicker?
The only way to answer these questions is often to try the action in question and see what happens. And sometimes the result is the car not being able to execute the driver's request, which is the definition of overdriving. The consequences can be tire smoke as the car skids off the track or a barely noticeable ignition cut as traction control intervenes.
Kinds Of Overdriving
An astute reader might recognize that there is a spectrum of overdriving situations, much as with driving in the first place:
- Prevented by the car: applies normally to excessive throttle input in a car with traction or stability control. The car senses that driving wheels are beginning to slip and reduces throttle, contrary to the driver's input. The result is the driver's action is not carried out, the car remains within physical grip limits at all times.
- Saved by the car: ABS is the best example here. The car reduces driver's inputs to the maximum possible given tire grip. The result is often the car deviating from the trajectory that the driver intended for it but staying on the pavement and facing the desired direction (i.e. not spinning).
- Saved by the driver: in a car without traction aids, the driver is tasked with correcting their mistakes. Usually the car ends up deviating from its intended trajectory and some smoke may be produced by the tires, but the car remains on track facing mostly the correct direction. This is roughly the minimal recoverable overdriving level on my tenths scale.
- Controlled two off: a more severe version of the previous case, the difference between what the car was asked to do and what the car could physically do was bigger, and the car was unable to stay entirely on the track. In a controlled two off the driver is able to keep the car going in the correct general direction so as to keep ample recovery room (at many tracks one can drive with two wheels off indefinitey without hitting anything). This is the roughly maximum recoverable overdriving level on my tenths scale.
- Four off or a spin: an even more severe development, now the gap between the driver's request of the car and the car's capabilities is so big that the car either flies off the track or immediately spins.
- Impact: this is when a car hits something. Depending on the track, this can mean the driver tried something in a track section with zero runoff (and hence may well have skipped stages 4 and 5 and went from 3 straight to 6) or that the driver has grossly misjudged the car's capabilities, or perhaps simply forgot where they were on track and what they needed to do.
As you see, there is quite a bit of variety when it comes to overdriving.
Cars without traction/stability control do not generally offer stage 1, and cars without ABS do not offer stage 2 either. Novice drivers generally lack the skills to execute stages 3 and 4. The result is that many people associate overdriving with stages 5 and 6 and often consider the affected driver "lucky" if they managed to stay on stage 5 and "unlucky" if they progressed to stage 6. But, drivers with appropriate skills can spend a lot of time in stages 3 and 4, and by doing so they learn a great deal about the capabilities of their car as well as get lots of car control practice, which makes such drivers even faster.
How does one go about finding the limits of their car and practicing car control without invoking stages 5 and 6 with the associated scolding from fellow track participants and car repair bills? The keys are reference points, small changes and offline exercises.
Reference points are a prerequisite for small changes. Your changes cannot be small if you have an imprecise baseline. Recognize that if you do not have a reference point in a particular corner, you are likely to be less consistent there and this means you need to be more careful to make small changes when you are experimenting with that corner.
Small changes seem like a no-brainer, except drivers do not always appreciate the magnitude of the changes they are making. Is half a brake marker (50 feet) a small or a big change? It is probably a small change for a novice that starts braking at the 500 board and a huge change for an advanced driver braking at the 300 board in the same car.
Finally, the offline exercises provide additional runoff room on pavement permitting the driver to be more aggressive with their driving. Should an overdriving event occur, the additional pavement will help to keep it on stage 3 rather than 4 or above.
Let's suppose now that a stage 4 or 5 overdriving event happened, for whatever reason. What do you do?
The simplest response to overdriving is to park the car, that is, immediately end the session. But if this is all you do, you are not learning anything from the experience, you do not improve your skills, and you do not get better at avoiding overdriving situations nor at recovering once they do happen.
It is said that good judgment comes from experience, and experience comes from bad judgment. To turn overdriving into a learning experience, follow these three steps:
- Identify what happened.
- Identify why it happened.
- Formulate a plan to prevent it from happening again.
Let's look at each of these steps in more detail.
First you need to know what happened. Sounds simple? Not quite. You want to identify a very specific and detailed cause. Ultimately you want the cause to be actionable. Supposed you had a four off, that is, the car left paved surface entirely. Consider these two answers to the question of "what happened":
- "The car spun."
- "One or both of the rear tires locked up under braking. I was applying steering input when the tires locked up. As the rear tires lost traction, the car rotated too much and spun."
Simply identifying the cause of overdriving will take practice and experience. The reason why novice track drivers are assigned instructors is because instructors can identify overdriving situations before they happen, or before they cause big problems.
Once you know what happened, you can develop a theory as to why it happened. Being able to accurately identify the "what" will greatly help figuring out the "why". In case of our hypothetical spin, the reason could be any of a number of factors:
- In a car with adjustable brake bias, too much rear brake bias.
- In a car without adjustable brake bias, but with aftermarket brakes, rear brakes may be too aggressive.
- Rear brake pad compound more aggressive than the front.
- Front tires are much better (have more grip) than rear tires.
- The car had too much steering angle when brakes were still on - excessive trailbraking.
- Rear suspension too stiff.
As the driver you can eliminate some of these options because they have preconditions. If you do not trailbrake, the second to last possibility will not be likely. If you trailbrake in a well balanced car, the same possibility will be extremely likely.
You can also notice that if your cause was "the car spun", your reason could have been "rear tires locked up", but if your cause was "rear tires locked up" then your reason might be "car had too much rear brake bias". In the management world, there is a technique called "five whys": when determining the root cause of a problem, ask "why" five times to progress from the most obvious, but likely surface, cause to the real, less immediately obvious cause.
Given a hypothesis for the cause of the problem, determine the corrective action to stay on track in the future. For our example, corrective actions might be:
- Adjust brake bias forward.
- Put larger front brakes on the car or run a more aggressive front brake pad.
- Put stock rear brakes on the car.
- Run identical tires front and rear.
- Do not trailbrake as late into corners.
- Soften rear suspension or stiffen front suspension.
As you drive in subsequent sessions, you want to back off a little in the corner where you overdrove the car, execute your corrective actions and try to determine if they are working. If the car spun, you should feel excessive rotation before it becomes unsalvageable. Is the car now rotating less? If yes, your hypothesis was likely correct. If no, you might need a new hypothesis.
Similar reasoning can be applied to recovery actions you took once you detected a problem. For example:
- What did I identify as a problem?
- When did I detect that something was wrong relative to how long the problematic situation already existed?
- Were my recovery actions correct in direction, timely, and correct in magnitude?
Let's examine these questions in more detail as well.
Often the actual problem and what the driver perceives are different things. In our example, the problem might be rear tire lockup but the driver did not feel the tires locking up - rather, the driver felt the car rotating excessively.
You can improve your problem detection on the track. For the case of rear tire lockup, if you have a rear wheel drive car it is likely that engine rpms dipped before the tires lost traction enough to cause unwanted rotation. By paying attention to engine note under braking you can detect excessive rear bias before it becomes a big enough issue to cause a spin.
The question to ask yourself is: "Could I have seen, heard or felt something earlier to realize that something was not right?"
There is inherently reaction time from when the problem develops to when you detect it. Good drivers work on reducing this time, i.e., recognizing problems earlier.
One example is locking up front tires under braking in a non-ABS car. When you realize you have a locked up tire, how long do you figure it has already been sliding?
If you run out of track at corner exit, what is the time (or distance) between you deciding what line to take out of the corner and how much throttle to apply, and you realizing that given that line and throttle input you will not fit into the track?
When you recognized you were in trouble and started to react, was your reaction decreasing or increasing the amount of trouble you were in?
Compare these two videos:
In both cases, driver (or instructor) chose to rotate the car. In the first video, rotation was performed into the turn which kept the car on pavement longer, scrubbing off speed, with the result being a damage-free four off. In the second video, rotation was performed away from the turn which resulted in the car completely missing the sand trap that it would have stuck in had it simply gone straight off, with the result being major damage to the car.
You typically cannot start recovering too early, but you definitely can start recovering too late. A good example would be not pressing brake and clutch hard ("both feet in") as soon as you figure out you are spinning. Drivers who have no drifting experience tend to start to countersteer too late when their car oversteers.
Did you try too long to correct the car at speed when you should have stopped?
When you were taking corrective action, did you go past the neutral point to create another problem? For example, drivers who are not trained to handle oversteer who manage to stop car rotation with countersteering often countersteer too much, resulting in the car rotating the other way, possibly into the outside wall.
You will get a lot more out of overdriving situations if you return to the track and finish the session, reducing your pace sufficiently to not overdrive again. While theoretical analysis is good, actually driving the problematic area again, at speed, and driving it correctly is extremely important.
The more you drive after overdriving incidents as opposed to parking, the better your endurance will be.