What is Understeer and How Can You Fix It?
At the last round of racing at Wakefield Park the #18 LBR Formula Vee spun several times during qualifying resulting in only two timed laps from a total of eight laps. Most of the spins occurred on turn 8, a technical turn known to drivers as the “Fishhook”. Compounding the loss of traction was a lack of track and air temperature which was hovering around 5*C making it hard to get any sort of meaningful temperature into the tyres.
It was not until after the session, and after talking with Dylan Thomas of CXC Racing, that the problem of understeer was identified as the main contributor to the off track excursions at turn 8.
During qualifying, Dylan observed that the #18 LBR Polar was suffering from severe understeer, particularly on the exit of turn 10, the last turn before entering the main straight. Having seen this Dylan then observed the car moving through Turn 8 and noticed that the driver was winding more lock on when the car didn’t immediately respond to his turn inputs due to understeer. This resulted in the front tires “biting” when they finally got traction and due to too much lock the back of the car was overtaking the front and voila the car would spin.
So what is understeer?
Understeer is when your car does not turn into a corner as much as you expect. During understeer the driver will feel as though the car is pushing the front wheels straight ahead even though the wheels are turned. This is ultimately caused by a loss of adhesion or traction between the tire and the road surface that results in the tire sliding or skidding across the surface of the road.
In this scenario the car will take a wider line through the corner and is likely to end up off the road or track on its exit from the corner. When a driver is experiencing understeer the only way to get the car to move through the corner as expected is to reduce speed/acceleration, allowing the tires to regain traction with the road surface or to straighten the wheels which will most likely result in you exceeding track limits – this is hardly ideal when you are racing and trying to move through corners as fast as possible.
Understeer is caused by an imbalance in the car and this can be corrected by adjusting your cars settings, so let’s take a look at what can be done…
How can you fix understeer?
The first concept one must understand is that weight distribution in a vehicle moves around when the car is braking or accelerating. This movement of weight has a big impact on how your car needs to be set up and how your car will respond when this weight moves. The next thing to understand is that driving style and inputs will also have a big impact on how your car performs prior to, during and on exit from turns.
The main components on your Formula Vee that will help resolve understeer are wheel alignment and suspension set up and the aim of these changes is to provide more traction at the front tires.
In order to improve responsiveness in steering it is recommended to run a couple of millimetres toe out on your front wheels. This is where the front tires point outwards and away from the vehicle centreline. Toe out on a rear wheel drive car theoretically will have an impact on the cars straight line speed due to increased rolling resistance however it will also assist with improved cornering delivering faster and sharper turning with less input from the driver, this is great for tighter tracks but it can also make the car more twitchy in high speed sweeping bends.
The other effect of toe out is tyre degradation and tyre temperature. Because the tires are pointing slightly away from each other tyre wear will be higher and due to the greater level of rolling resistance the tires will come up to temperature more quickly.
The other component to adjust is suspension. In adjusting suspension, you want to increase grip levels at the front wheels when braking and moving through a corner, in order to achieve this, you may need to soften your front suspension and reduce front ride height. More importantly you will need to increase rear suspension by adjusting your rebound rate and increase the spring which will also have the effect of raising the rear ride height and transferring more weight (and therefore grip) to the front tires.
As with all setup changes it is important to document what you have changed just in case the changes compound the original problem or introduce a new problem, this will make it easier for you to revert your changes back or to identify what impact the changes have had.