All of your actions while driving a car at the limit are dictated by the limits of your tires, and the limits of your tires are represented by The Friction Circle. The Friction Circle is a way of looking at how inputs interact with the maximum amount of grip of your tires.
The Limits of Grip
As you know, there is a set amount of grip for any given tire. The limits of grip are easy to ascertain and comprehend when you are doing one thing. Give your car too much gas and the wheels will spin. Brake too hard and you will lock up the wheels. Turn too aggressively and your tires will slip. But what happens when you do more than one thing at a time? Say, give your car gas while cornering?
The answer is that there is a set amount of grip that a tire will exert in any direction. Exceed that limit, like giving the car gas while cornering, as in the example above, and the tire will slip and lose traction. When you brake or accelerate, the tire exerts a grip forward or backwards. When you turn, it exerts a perfectly sideways force. When you turn and brake or accelerate, it exerts a force sideways, but not at 90 degrees to the direction of travel.
Say you are braking hard and turning slightly. The tire exerts a force mostly perpendicular to the direction of travel, but slightly to the side. Brake less and turn more and the direction of the force rotates more perpendicular to the direction of travel. The exact direction of grip force isn’t that important, what matters is that the overall level of grip is constant, regardless of direction.
Let me say that again because it is so important: the overall level of grip is constant, regardless of direction. That is the logic behind The Friction Circle. What it means is that you cannot brake or accelerate at the limit and turn at the same time. If you do, you will be asking your tire to provide more grip than it is capable of providing, and it will slip.
Lessons from The Friction Circle
So what does this mean in practice? It means that you have to be mindful of your inputs. If you are braking at the limit and want to turn, you need to let off of the brake slightly. Likewise, if you are turning and want to accelerate, you need to straighten the wheel slightly. Sounds simple, right? In theory it is. The hard part is learning the balance between turning forces and braking/accelerating forces. That comes with practice and seat time.
on February 25, 2007 at 3:37 pm The Pansy Patrol - Info for the 3000GT / Stealth Community wrote:
[…] However, you can’t just get on the throttle earlier and expect everything to turn out fine. If you read The Friction Circle, you’ll see that if you try to accelerate too hard while at maximum cornering grip, your driving wheels will lose traction and slip. In a front wheel drive car, you will understeer, and in a rear wheel drive car, you will oversteer. Both conditions are undesirable, and will make you slower through the corner. […]
on February 28, 2007 at 11:26 pm The Pansy Patrol - Info for the 3000GT / Stealth Community wrote:
[…] Understeer Imagine that you when you are cornering, your rear wheels have plenty of traction but your front wheels lose traction. Since your front wheels don’t have any more traction to make the car turn, your car will continue to move in a straight line regardless of whether you turn the steering wheel more. This condition is known as Understeer. Alternatively, you might hear it referred to as “pushing” or “plowing.” Correcting Understeer The best way to fix understeer is slow the car down. To do so, you should straighten the steering wheel and get on the brakes. As described in The Friction Circle, there is a limit to the amount of grip of your tires. If you are understeering, you have exceeded your tires’ limit of traction. For the same reason that turning the steering wheel more will not make the car turn, hitting the brakes will not make the car slow down appreciably. To regain braking traction, you need to unwind the steering wheel, transitioning the gripping force from a sideways cornering force to a straight braking force. When you have bled of some speed, you can then finish turning through the corner. Though this is not the best Line to take through a corner, it is the safest and most effective way to deal with Understeer. If you are understeering, you are already off of the best Line, so just slow down as quick as possible so that you can quickly get back on the Line. […]
on April 1, 2007 at 10:48 pm The Pansy Patrol - Info for the 3000GT / Stealth Community wrote:
[…] But on a track, you want to be on the gas as much as possible. If you brake completely before a corner, then the entirety of your braking zone is on the previous straightaway. Since straightaways are where we can go fastest, the more time we can spend accelerating on them, the faster we will get around the track. The way to gain more gas time on a straightaway is to extend the braking zone into the corner itself. This is where trailbraking comes into play. Trailbraking and the Friction Circle If you read The Friction Circle you should be saying to yourself, “I can’t brake at threshold and begin turning or I will exceed my tires’ grip.” You’re right! You cannot. What you can do is brake almost at the limit and begin to turn. When you trailbrake, you transition your braking traction into turning traction. […]
on September 24, 2007 at 11:42 am The Pansy Patrol - Info for the 3000GT / Stealth Community wrote:
[…] This will slowly transfer the rear tires from cornering grip to braking grip, as we discussed in The Friction Circle. I have this down to a reflex now. Whenever I hit the brakes in a corner, I unwind the wheel a […]