When driven under acceleration with no brakes applied, a front wheel drive car will understeer when the front wheels are turned. To overcome the understeer, a technique called left foot braking is used to change brake bias (balance) to the rear. By using a combination of throttle and brake you can change from understeer to neutralsteer to oversteer. How does it work? Read on! |
Think about this for a second. When you stand on the throttle, which way does your body try to go? Toward the rear wheels! Right? Now what happens when you brake? Your body tried to go forward! This boys and girls is weight transfer! By using the basic rules of weight transfer and a combination of throttle and left foot braking, you can be in control when the unexpected happens on a rally (which always happens)
How Does It Work?
Brake bias in normal street rally cars is toward the front wheels for safety reasons. If you have ever pulled up your hand brake when turning on a wet road and spun out, you know why they build cars this way. What you did was bias the brakes to the rear, and this is not what Grandma wants in her Buick coming home from the supermarket. But as rally drivers we can use a means of biasing the brakes to the rear. Some of the things that can be done include using a brake bias control valve or installing more powerful brakes on the rear wheels. That works wonderful on a track, but on a rally it's hard to change your brake bias in the middle of a turn that suddenly changes from dry dirt with good grip, to wet slime with no grip.
Enter Left Foot Braking !
Once your have mastered LFB, when the road surface changes, you can change the Rally Braking bias by either adding power or brake pressure ( this is also called "modulating"). Example: You are in a turn and the rear of the car starts to slide out more then you want. You could release some brake pressure and increase the throttle. This will change the oversteer to understeer. The reverse is also true. If the turn tightened, you can change to rally oversteer by increasing brake pressure against the throttle. Also by balancing the brake and throttle you can get a neutralsteer.
Why Does It Work?
A tire has 100% of it's possible traction when it is rolling straight with no braking or acceleration. When you change any of these factors the tires affected will have less available traction and break loose earlier.By applying brake against the throttle in a front wheel drive car, two things happen. One: The front wheels keep turning. And two: The rear wheels try to lock up. If you are in a turn, the back of the car will start to slide toward the outside of the turn. To control or stop the slide, apply less brake and more power ( this changes the oversteer toward understeer and stops the rear wheels from sliding toward the outside of the turn ).
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