(049) UNDERSTEER AND OVERSTEER (3 of 13) Intelligent Racing, Minimal Spending: The Definitive Introduction To Racing Concepts

Understeer/Oversteer

Welcome to the second installment of this racing concepts series. Remember: the most dangerous words in the English language are “I already know that.”

Let’s do this.

High-performance driving is all about thinking ahead. If you’re driving your vehicle on the edge you will, at some point, lose control of it.

There are two ways that you can lose control of your vehicle-oversteer and understeer.

Knowing what these conditions are, how to avoid them, and how to correct them are critical.

With the following knowledge you will have a fair shot at anticipating them, and with any luck, avoid them all together.

Understeer

Understeer is when the front tires lose grip before the rear tires (Figure 5).

understeer 1

 

Example: Pretend a racecar is going down a straight toward a corner that normally isn’t problematic.

On this occasion, however, the driver begins to enter the corner with far too much speed – a speed that is above the front tires ability to grip the track surface.

Since the front tires don’t have enough traction to turn the vehicle, it will begin to understeer (Sometimes called plowing, pushing, or being tight).

Regardless of how much the driver turns the steering wheel, the car will continue in the direction it was originally traveling.

This doesn’t always mean the driver made a mistake in technique. Understeer can be caused by other factors, such as an oily surface that reduces traction between the front tires and driving surface.

Other contaminates, such as water, sand, grass, or even small chunks of rubber (often referred to as marbles) from another cars’ degraded tires can have the same effect.

The problem could also be as simple as the weather.

Colder ambient temperatures can keep tires outside of the their optimal operating temperature range, restricting their potential grip.

In addition, worn out racing tires on your own car might not be providing the same level of grip as in previous laps.

 

Correcting Understeer 

There are a number of ways to correct understeer, depending on how wide the race track is and how much faster the driver is going compared to the front tires ability to grip. If the driver only exceeded the front tires ability to grip by a small amount, he has a very high chance of correcting the understeer. There are four things he can do:

  1. He can unwind the steering wheel (turn it slightly less).If there is enough room on the track for him to create a wider arc, increasing his turning radius may be enough for the front tires to begin gripping again.
  2. He can apply a small amount of extra braking.This will shift more weight to the front of the vehicle, increasing the vertical load of the front tires and providing more traction.If the load does not exceed the tires capacity of grip, extra traction may be enough for the front tires to begin gripping the track again.We’ll talk about vertical load later.
  3. If he is on the throttle, he can lift.If the car began to understeer at the corner exit after he began applying the throttle (perhaps he jumped on the gas too hard (or too soon) and more weight shifted away from the front tires then he expected), he can simply lift off the throttle and cause a small amount of weight to transfer back to the front end, thereby increasing traction.And when I say lift I don’t mean taking the foot off the pedal.A small decrease in throttle can often fix the problem. Adjust as necessary.
  4. Enjoy the ride.If the driver entered the corner with far too much speed, there may be nothing he can do to correct the problem.At this point he’s along for the ride at the mercy of physics, until his speed decreases enough to regain enough traction to make a positive change.

NOTE: Some drivers, especially new ones, have a tendency to turn the steering wheel more during understeer. Well, stop it! It will further decrease traction and ensure an off-the-track excursion.

A combination of these may be the best bet. Unwinding the steering wheel and inputting a dab of brakes is often the safest way to get back on track.

In any case, the driver has blown the corner and therefore the entire lap.

 

Oversteer

Oversteer is when the rear tires lose traction before the front tires (Figure 6).

oversteer 1

 

Example: A racecar is heading down a straight that leads into a right hand corner.

The driver enters the corner in a way that exceeds the rear tires ability to grip the track surface.

This causes the rear of the car to slide out of line toward the outside of the corner.

The vehicle will begin spinning out of control as the rear attempts to pass the front, toward the outside of the corner.

There are multiple scenarios that can lead to an oversteer.

  1. The driver brakes too abruptly before entering the corner.Notice I didn’t say he applies too much brake. An abrupt application of brakes causes a radical weight transfer toward the front of the car, making the rear end light and reducing traction at the rear tires.Since the rear tires can’t grip, they begin to slide out of line.A smoother application of brakes can cause less weight transfer and provide more traction
  2. The car does not have a neutral set up.There are many mechanical maladjustments that can induce an oversteer.Perhaps the rear anti-roll bar is too stiff, or the rear toe is off, making the car unpredictable and feisty.Maybe the brake bias is set rear-heavy, or the car is  experiencing bump-steer.
  3. The driver applies too much throttle at the corner exit.In a rear-wheel-drive car, this causes excess wheel-spin at the rear wheels and radically reduces traction.If the driver doesn’t let off the throttle and let the car settle down, the rear of the car will try to pass the front.

The same outside factors that could induce understeer can potentially cause an oversteer.

Again, thinking ahead is the key to avoiding both.

 

Correcting Oversteer

Purposeful oversteer (popularly known as drifting) can be absurdly fun and is a beautiful exhibition of advanced car control.

Being surprised by an unexpected oversteer, however, is much less enjoyable.

There is only a very small window of time to correct an oversteer. The faster the car is going, the harder it is to save.

But, like in most situations, there are a few things that can be done to correct it.

First of all, don’t apply the brakes. During an oversteer many young drivers tend to panic brake.

But think about it: oversteer is caused by a reduction of traction to the rear tires. Remember what the previous weight transfer post stated about applying the brakes? Braking shifts weight to the front. In this case, it will only make the rear end lighter, further reducing traction of the rear tires.

Be ready to countersteer. Countersteering is the act of pointing the front tires in the direction you want to go.

If you experience oversteer in a right hand corner, you will have to countersteer to the left.

During oversteer the front end of the vehicle will act as a pivot point as the rear tries to pass the front. Countersteering removes the pivot point and may keep the rear end from sliding too far out of line.

At this point, the driver is hoping that the car has slowed enough for the rear tires to regain traction and return to its normal position.

Be ready to uncountersteer. If the oversteer can be saved, the rear tires will regain their grip and begin to fall back in line.

If the driver is still countersteering when this happens, the corner will still be pointing to the right, but the steering will be pointed left. Always be ready to straighten the steering when the rear starts to come back in line.

If the entry speed is too high, or countersteering does not occur quickly enough, there may be nothing you can do to save the oversteer. Anticipation is the best way to negate or correct it.

Summary

  1. Understeer is when the front tires lose grip before the rear tires.
  2. Oversteer is when the rear tires lose grip before the front tires.
  3. The best way to avoid both is anticipation. If you can’t avoid them and you have to make corrections, the best way to regroup is still anticipation.


NEEK WEEK: Track Analysis

The next part in this series is only a week away. Go back and read through this again. Make sure you truly understand what you just saw, because the series progressively builds as it continues.

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