Lesson 13- Oversteer or/and Understeer!
Welcome to Lesson 13 of SpeedScienceHQ. As a racing enthusiast, you must have heard of the terms Understeer and Oversteer, whether it's during karting or drivers complaining about these in Formula 1. Understeer and Oversteer are the major components behind deriving the perfect setup for a racecar and giving feedback about these should be accurate. In this lesson we will understand what Understeer and Oversteer are and why they are caused. In the next lesson we will see how you as a driver can correct it and also how to "set up" a racecar to cater to these needs.
Understeer
The simple definition of understeer – also known as ‘push’ – is when your car doesn’t turn as much as you ask it to with your steering input. Quite literally the car is ‘under-steering’ due to an imbalance in grip between the front and rear of the car.
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The car will have broken traction at the front, and the front tyres will slide across the track surface, however, the rear tyres will still have grip. Therefore, the car is imbalanced and at that particular point in the corner, you are limited by front grip.
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The drawing below shows the intended line by the driver (orange) and the path a car with understeer (green) would take.
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The following diagram shows two paths through a corner. The orange line is the intended, and ideal, racing line. The green line shows a racing line where the front tyres have lost grip and the car has understeered wide. You can see that from the turn-in point the car hasn’t turned as much as the driver wanted, the apex has been missed and the car runs wide at the exit.
Summary of understeer:
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A driver arrives at the given corner
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They turn in towards the apex
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The front tyres break traction and slide across the track surface
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The car doesn’t turn as much as the steering angle input
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The car runs wide of the intended racing line
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Understeer - What does it feel like
When understeer occurs and the front tyres break traction, it’s actually quite predictable and easy to resolve. Oversteer, where the rear tyres break traction, is actually much harder to balance and we’ll go into this in the next tutorial.
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The feeling of understeer is subtle. Imagine turning your car into a corner – the steering wheel will have a nice weight and feel to it. If, as you’re coming into the apex, the front tyres break traction and being to slide, the turning resistance from the steering wheel will become less – it’ll feel less ‘loaded’.
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The temptation here is to apply more and more steering angle, as the car isn’t turning as much as you’d like. However, the tyres are already beyond their grip threshold and cannot turn anymore, so applying more steering angle is pointless. In fact, it’s really poor technique as when the front tyres grip again they’ll be pointing in the wrong direction!
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It’s important to not hold on to the steering wheel like you life depends on it (although it probably does). If you’re gripping the wheel tightly you’ll lose some feeling – have a relatively relaxed grip, that way you’ll feel the car more.
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When you feel the car begin to understeer, don’t just apply more steering. Keep the car on the edge of traction and what’s most likely is that you’ll have to reduce you speed somewhat – something we’re going to go over a little later.
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What are the causes of understeer:
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1) BRAKING TOO HARD:
In our last tutorial, we covered the vast topic of braking (see tutorial here). As we mentioned there, it’s possible for the braking phase to affect the grip balance of the car at turn-in.
If the grip in the car’s front tyres is being completely used up for deceleration and then the driver asks them to turn as well, it’s just too much load for the tyres to take and they’ll break traction at turn-in.
Once traction is broken the driver will have to slow the car quite significantly to regain grip at the front, which of course will cost lap time.
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2) ENTERING A CORNER WITH TOO MUCH SPEED:
It’s possible to cause understeer by simply entering the corner with too much speed. There’s only a certain amount of speed a car can physically take through a corner – try and take more than this and the car will break traction.
Whether your car loses grip at the front or rear at this point will depend on setup and driving technique, but if the driver comes off the brakes early (allowing weight and grip to transfer to the rear of the car) he’ll likely understeer passed the apex.
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3) ACCELARATING TOO MUCH THROUGH THE CORNER:
If you accelerate too much from the apex of a corner, and you car’s setup isn’t perfect, it’s likely that you’ll induce some understeer. This happens because when you get on the accelerator, the rear of the car will squat causing a rearwards transfer of weight and grip. This leaves the front of the car with little traction and so creates an imbalance.
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4) POOR CAR SETUP:
If your car isn’t well set up, whether it be springs, dampers, roll bars or any of the many things you can change, it could cause understeer.
Setting a car up is all about maintaining a good balance – an equal distribution of grip – through all points of the corner as the forces on the car change. I’ll go into more detail regarding how to resolve understeer issues with setup a little later in the article.
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Oversteer
Oversteer happens when the car is turning and the driver applies more power than the tyres can deal with. This makes the tyres slip and try to push in the opposite direction to the turn, kicking the back end of the car out. Pretty much the opposite of understeer.
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The diagram below shows a car’s racing line when it’s oversteering on a circuit. As you can see, the driver has started to oversteer before the apex and failed to correct the slide, before spinning to the inside of the circuit.
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Understeer - What does it feel like
When oversteer happens and the rear tyres break traction, it’s quite easy to feel. A driver will sense the movement – the rotation of the car – in their bum and through their body.
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When this movement happens, the driver will need to react quite quickly, as if there’s no opposite lock input, the car will likely spin. If the correct amount of opposite lock is applied, the car will continue to oversteer a little through and out of the corner, which is what we’re after.
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When a car oversteers, most people have a natural reaction to add opposite lock. With beginners, the reaction can be a little late and the input a too much, but this is to be expected.
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With time and more oversteer moments, a driver will begin to predict when oversteer is about to happen – rather than reacting to it.
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When I sit next to an amateur for coaching, a lot of the time I know when the car is about to slide a second or so before the driver. This is because of my experience, but the truth is it can be learnt – pretty quickly – if a driver continually drives their car on the edge of grip and has a lot of these small oversteer moments.
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What are the Causes of Oversteer:
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ENTERING A CORNER TOO FAST:
There is a limit to how fast a car can travel through a certain radius. Ask the car to go through a corner above this speed and it will break traction. Depending on the setup of the car, and the drivers technique, the rear of the car can lose traction before the front and cause oversteer.
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ENTERING A CORNER WHILE BRAKING TOO MUCH:
I spoke about this in the weight transfer video tutorial but I’ll go over it briefly here again. When a driver brakes the front suspension compresses, transferring weight – and grip – to the front of the car and away front the rear.
This leaves the grip distribution of the car unbalanced and the front with the majority. If the driver turns in with the grip distribution like this, the front will turn in very well, but we will be rear grip limited and the car will likely oversteer.
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TURNING INTO THE CORNER TOO VIOLENTLY:
Much like entering the corner too fast, turning in too violently can create understeer or oversteer – which end slides first will depend on the car’s balance and setup.
Having said that, turning into a corner violently is never good technique and if you do this, you’ll be losing lap time.
If the car has more front grip and a driver turns in sharply, the car will oversteer and it won’t be predictable or smooth. Violent inputs cause violent slides, which are more difficult to catch.
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LIFTING OFF THE THROTTLE:
Lift-off oversteer’ spins and crashes are the most common incidents I see on track days and with amateur racers. Following is the order of what usually happens in this case:
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The driver enters the corner
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They bring the car to the apex and begin to get back on the throttle
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Their vision isn’t far enough ahead, and they begin to run wider than the ideal line
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When they’re almost at the exit, the driver realises they’re too wide and running out of track
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The driver lifts off the accelerator and turns sharper to keep the car on the track
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Due to the increase steering lock and weight transfer the car spins towards the inside wall
Lift off oversteer isn’t a very pleasant type of oversteer, it can often feel quite snappy and it usually happens because a driver is not looking far enough ahead.
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ACCELARATING TOO HARD- (ONLY IN A RWD CAR):
It’s possible to lose traction at the rear of the car by being too violent with your right foot. If a driver is too hard with the accelerator, more so while cornering than in a straight line, the tyres may become overloaded and begin to slide.
As I described in our grip article, there is only so much grip a tyre can give – if you ask too much of it the rubber will inevitably break traction.
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POOR CAR SETUP:
Having a poorly setup car is always going to cost you time. A good driver can control oversteer, however if you’re not using 100% of both the rear and the front tyre’s grip, you’ll be losing time.
In the case of a poorly setup car that is rear grip limited (oversteery), a driver will be using 100% of the rear tyre’s grip, but less than 100% of the front. Therefore, it would be ideal to alter the setup so the car is more balanced and using 100% of the grip available across all tyres.
As I mentioned in our understeer article, changing setup – or rather improving setup – can be very challenging. You need to ensure your driving is consistent, your feeling and understanding of vehicle dynamics are good and that you can relay this information to a race engineer who can then make the correct setup change.
If you feel like you have a poorly handling car, it may be worthwhile hiring a professional driver and an engineer to help get you a decent base setup. It can help improve a car, both regarding overall grip and possibly, more importantly, driveabilit
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