Understeer vs Oversteer Simply Explained
Below you will find basic explanations of understeer vs oversteer. Some charts (for the brave) and a nod to the proper explanation (for the purists.)
When you are looking to cure a handling issue or trying to find more speed in your racing car, ensuring everyone is talking about the same thing is key.
The terms understeer and oversteer are used with abandon, yet definitions can vary wildly – from the highly technical to cringe worthy analogies to do with whether you see the tree you crash into or not …
Whilst I suspect most end up coming to their own definitions of what these terms mean, I feel having a common understanding you can reference should be useful.
A Nod To The Proper Explanation
There is a “proper“, highly technical, explanation of what understeer vs oversteer is.
This involves analysing the difference in tyre slip angles front to rear, the resulting body side-slip angle and corner radius. In tackling that explanation, it would also need to tell you how any car balance is likely to also be proportional to your racing car speed.
Once you’ve got your head around all the concepts and maths, it would then need to reveal that the explanation is only for a quasi-static vehicle state. A state that your racing car, as a highly dynamic vehicle who’s sole aim is to maximise its available acceleration capacity at all times, should never be in.
Then, if you had not lost the will by that point, the explanation would need to cap it all off by also adding that a racing cars aerodynamic, drive train and chassis characteristics (as well as the rate at which a racing driver applies their inputs and the track topology) can further contribute to vehicle behaviour that looks and feels like understeer vs oversteer but isn’t really – well not technically anyway.
Still with me? 😀
It actually goes on further (like what is involved to accurately measure understeer vs oversteer) but, I’m sure you get the idea – it is complicated.
If I tackled it I’d get bits wrong and the technical purists (who have no interesting in actually helping others) would argue with me. So …
This is not that proper definition but instead a simple one. In fact two.
Simple Explanation of Understeer vs Oversteer
Here are two simple definitions for you to use.
The idea is for a common definition for when drivers are giving feedback or for when you are discussing how to cure handling problems or find more speed:
Understeer is where the racing car will not follow the trajectory that the racing driver is requesting and results in the driver having to apply more than ideal amounts of steering lock.
Understeer in racing driver talk: “The front has no grip.“
Oversteer is where the racing car rotates faster than the racing driver wants and results in the rear of the car becoming unstable.
Oversteer in racing driver talk: “The rear has no grip.“
Whilst that has given you a basic explanation of understeer vs oversteer the bonus section below has some further considerations for you … 😉
Bonus Section (Understeer vs Oversteer with Charts!!)
Think of this as a kind of introduction to the more technical explanation. However it is only aimed at helping you consider what is happening in practise.
This should help you to better understand how any car changes are effecting your racing car’s understeer vs oversteer balance.
Racing Car Rotation verses Steering Wheel Angle
When the driver turns the steering wheel, they want to have the racing car turn (or yaw or rotate) in proportion.
If they turn the steering wheel twice as much they expect twice as much rotation – a bit like what you expect of a volume control I suppose.
This is relationship sometimes referred to as “steering linearity” and for a balanced, good handling car it is what you are after.
Have a look at the chart below:
You can see three lines; one for the balanced car and one each for understeer and oversteer.
For a balanced car you can see the line is straight. This means that as the steering wheel is turned, the racing car rotates in linear proportion. The racing driver will say this car feels balanced which is a good.
With the understeer scenario, as the steering is turned the line (dotted blue) curves up.
What this is saying is that as the racing driver applies increasing steering wheel angle, they are getting a decreasing reaction from the car.
The rotation amount is not linear with steering input and in fact, it gets to a point where the driver cannot get the car to rotate anymore no matter how much extra steering angle they add.
Whilst a stable situation, to get the car around the corner the driver often has to slow down. So excessive understeer is not good in a racing car.
The oversteer scenario (red dotted line) is the opposite. As steering is applied the racing driver is getting an increasing amount of racing car rotation.
With oversteer, the racing car becomes very sensitive to driver steering inputs. This increases the chance of a spin and makes the racing car feel very unstable (even scary!) to the driver. If a racing driver does not have confidence in the car they are likely to drive slow. So excessive oversteer is not good in a racing car.
Reinforcing This. Worked Example.
If you look at the next two charts you can see this more clearly:
In this first chart, the racing driver is looking for a small amount of rotation from the racing car.
With all three scenario’s there is not much difference between the amount of steering wheel angle the driver needs to apply.
In the next chart, when the racing driver wants (approximately) double the rotation from the racing car you can see where the differences come in.
For the balanced car, they need to apply about twice the amount of steering. In the understeering car the racing driver needs to apply nearly three times the amount of steering angle. With the oversteering car the driver has hardly had to apply any extra steering lock.
Whilst oversteer does have some performance benefits (less steering = less resistance = more potential speed) the trade-off you have to make is how much extra work load this adds to the racing driver.
No More Understeer vs Oversteer Confusion
Hopefully this has got you thinking. Next time you have an understeer vs oversteer conversation, hopefully no-one will be confused. Feel free to bring this explanation up (even show people the charts) if it helps you further.
Enjoyed this? Check out these other articles:
Want to take the guess work out of setting your tyre pressures? Try this article including a free calculator: https://www.yourdatadriven.com/how-to-set-your-racing-car-tyre-pressures-perfectly-every-time/
Wondering what the tyres are actually doing? This article should help your visualisation:https://www.yourdatadriven.com/tyre-slip-angle-explained/