Understeer & Oversteer Correction

Publication: Total Magazine Article 2009

Have you driven the “Ring” in November? I’ve recently returned from a wet and wintery 4 day visit, honing my grip limit driving and enjoying the empty circuit. Tip toeing through high speed corners and ever changing gradients, the multitude of changing road surfaces adding a degree of driving complexity no other circuit can match. But what happens if your Nissan/Evo/Subaru gets out of shape? Are you comfortable correcting understeer or oversteer?

It is difficult to convey the dynamic feel required to control a vehicle driven at its limit of adhesion through words on a page. However I can answer some of the questions and queries that are often asked and explored on our drifting courses. Using Caterham 7s we regularly deliver one to one Drifting courses. The same questions come up time after time – let me share some of them with you.

What is Understeer?

If my vehicle is understeering, the front of the vehicle is travelling quicker than the rear. It is steering less than I need to negotiate the turn. Imagine driving on a large circle at grip limit as I increase power – the front of the vehicle will leave the circle.

What is Oversteer ?

If my vehicle is oversteering, the rear of the vehicle is travelling quicker than the front. It is steering more than I need to negotiate the turn. Driving the same circle at grip limit as I increase power, the rear of the vehicle will leave the circle.

When my car oversteers in a corner I don’t seem to be able to stop it spinning.

Inexperienced drivers have a tendency to react much too slowly and too conservatively on the steering wheel when attempting to control an oversteering vehicle. Counter steer input has to equal oversteer angle in order to correct the slide. In essence, if the back of the car steps out by 30 degrees, it will take a 30 degree counter steer(turn into the slide) at the steering wheel to correct the slide and see you heading off in the intended direction. Problems can occur if the driver has not sensed the speed of the oversteer (Yaw rate). Your counter steer needs to be at the same rate as the yaw rate. Let the car get too out of shape and ahead of your counter steer and the car will spin. Work your hands at a speed that is ahead of the yaw rate and you will find it easier to correct the slide.

Why do I see drivers momentarily letting go of the steering wheel when their car over steers? Clarkson, Tiff, Plato all do it why?

It is simply to allow the steering angle to equal the yaw rate of the vehicle. If the vehicle oversteers aggressively it may not be possible to counter steer quickly enough to arrest the slide. Momentarily releasing your grip on the wheel allows the yaw rate and steering input to equalise. Only try this under supervision with an instructor, and in a safe environment. It takes practice to perfect.

What should I do with the accelerator when my car is oversteering?

Complex 4 wheel drive, yaw control and stability systems can help to correct a sliding vehicle and, depending on the system, can proportion drive away from the over speeding wheels aiding correction and corner exit speed. What they can’t do is defy physics. They can only help manage the available grip between the tyre and the road. The safest advice is to smoothly and precisely reduce the amount of power to the over speeding wheels gently. Getting out of the gas will aid recovery. It is important not to snap the throttle shut as the vehicle needs some forward driven motion to aid recovery. If you are driving a front wheel drive configuration then the opposite applies. Increasing power helps to pull the front of the vehicle straight.

Why does my car inherently understeer through a corner on circuit?

It is a safety issue. Manufacturers irrespective of the configuration and drive train layout of the vehicle, tune understeer into a vehicles platform as it is safer. It is less complex to correct than oversteer – it’s correction is instinctive: ease out of the gas pedal and the understeer will reduce. For the general public and the untrained driver it reduces the risk of a crash. Oversteer correction is a complex process requiring timely and accurate counter steering input from the driver. It is a skill that needs practice and often tuition to perfect. When faced with a dangerous driving scenario, oversteer correction is not as instinctive as simply reducing your foot pressure on the gas pedal to reduce understeer.

My car handles differently when driven through left and right hand corners. Is it me or the car?

I have lost count of the cars I have been in at Millbrook that once on the Steering Pad, the circuit where we explore understeer and oversteer, they behave inconsistently. Our own training car – a Classic Subaru – last year left a puddle of oil on the garage floor around the near side rear wheel. The rear damper seals had let go. A rebuild of all four dampers has breathed new life back into our trusty work horse.

Track days accelerate the wear rates of many components, so it pays to be vigilant with your maintenance. Running heavily over kerbs and rumble strips is enough to change geometry settings and damage wheel rims. Periodic alignment checks will help to keep your vehicle pointing in the right direction through corners. If you have adjustable dampers fitted, make sure the settings are as intended. Handling irregularities can simply be incorrect settings side to side. This regularly seems to be the case when clients have recently purchased their vehicle and not checked the settings.

Where should I be looking if my car oversteers through a corner?

The simplest advice is often the most effective. If you are all out of shape through a corner don’t forget to keep looking where you want the car to go. Over grip limit driving, as with all driving activities, is based on looking in the correct place. You may be surprised at the drift angles you can recover from if you keep looking at the tarmac and not the scene of the accident.

Take care through the winter months and look out for those track day winter bargains. Yes the speeds are slower if it’s wet, but you can have just as much fun.

Safe motoring

Colin Hoad

CAT Driver Training Ltd.

Tel. 01234 757633

Email info@catdrivertraining.co.uk

catdrivertraining.co.uk

COPYRIGHT CAT DRIVER TRAINING LTD. NOVEMBER 2009

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