Introduction: Looking at Cornering from the Rear Tires
In another article, I discussed how front-tire grip can be divided between braking and turning: Why the GR Yaris Pushes Wide ★ Cornering Without Trail Braking and Using All Four Tires.
This time, I want to look at the same cornering process from the opposite end of the car: the rear tires.
What exactly are the rear tires doing during braking, turning, and acceleration? And how does longitudinal weight transfer change the amount of grip available at the rear?
Let us examine the process step by step.
Heavy Braking: Weight Moves Forward, but Rear Grip Does Not Disappear
The thought experiment is simple.
The car begins on a full-throttle straight, enters a corner, and eventually returns to another full-throttle straight.
First comes heavy braking at the end of the straight.
In this model, the steering wheel remains straight during maximum braking. The objective is to reduce speed as much as possible over a short distance, producing strong forward weight transfer.
If steering input is added while the front tires are heavily loaded, a large yaw response can be generated. Some driving techniques deliberately use this effect to initiate rotation, but that is not the approach considered here.
For this discussion, braking and turning are treated as separate uses of front-tire grip.
Near the end of heavy braking, a large proportion of the vehicle’s load has transferred forward. The rear suspension extends and the vertical load on the rear tires decreases.
But rear-tire grip does not become zero.
As long as the rear tires remain in contact with the road, they still retain some grip. That remaining rear grip plays an important role in stabilizing the car during the transition into the corner.
Initial Turn-In: The Front Tires Turn the Car, the Rear Tires Stabilize It
Once heavy braking is complete, steering input begins and front-tire grip is used primarily to generate cornering force.
Because substantial load may still remain on the front axle immediately after braking, the front tires can generate strong lateral force and produce a rapid yaw response.
But imagine that the rear tires had completely lost contact with the road during braking.
The front tires could then generate yaw while the rear of the car had almost no ability to resist lateral motion. The mismatch between the car’s inertia and its changing heading could easily develop into a spin.
This is one reason why maximum braking still has to remain within the range where the rear tires retain meaningful contact with the road.
In reality, most cars do not immediately spin during turn-in because suspension travel allows the rear tires to remain on the road, leaving enough rear grip to resist excessive lateral movement.
This reveals one of the rear tires’ most important jobs during cornering:
they resist lateral sliding and stabilize the rear of the car.
Mid-Corner: How Much Rear Grip Can Be Used for Acceleration?
While the rear tires are resisting lateral sliding, the driver also wants to begin accelerating as early as possible.
This makes it useful to think of rear-tire grip as being divided between two jobs:
- lateral grip used to keep the rear of the car from sliding outward;
- longitudinal grip available for acceleration.
During cornering, part of the rear tires’ available grip is continuously being used to generate lateral force.
Whatever remains can potentially be used for acceleration.
Early in the corner, however, the rear axle is still relatively lightly loaded because of the previous forward weight transfer under braking. The rear tires therefore have less total grip available than they will later in the corner.
A large proportion of that limited grip may already be required simply to stabilize the car laterally.
This leaves relatively little grip for acceleration.
If the driver suddenly applies too much throttle at this point, the rear tires may exceed their available grip, begin to slide, and produce power oversteer.
The driver’s job is therefore to begin opening the throttle carefully, searching for the amount of rear grip that remains available for acceleration.
A small amount of throttle is applied while steering angle is still present.
If that throttle input remains within the tires’ available traction, the car begins to accelerate. Acceleration transfers load rearward, increasing vertical load on the rear tires and therefore increasing the amount of rear grip available.
But this additional grip cannot automatically be devoted entirely to acceleration.
As vehicle speed rises, the rear tires may also need to generate more lateral force to maintain the same curved path.
The driver therefore continues increasing throttle while constantly judging how much rear grip remains available after the lateral demand has been satisfied.
This progressive process is one of the central tasks from mid-corner to corner exit.
Acceleration Versus Understeer
If acceleration continues successfully without producing oversteer, two things begin happening at the same time.
First, rearward weight transfer increases rear-tire loading, which improves traction and allows stronger acceleration.
Second, that same weight transfer unloads the front tires.
As front-tire load decreases, the front axle has less available cornering grip, making understeer more likely.
The driver is therefore trying to achieve something very specific:
the greatest possible acceleration without causing the front tires to lose the lateral grip required to hold the intended line.
This balance between acceleration and understeer is one of the most delicate sensations in performance driving.
What Zero Steering Angle Means at Corner Exit
As the car approaches corner exit and its direction begins to align with the straight ahead, the driver progressively unwinds the steering.
As steering angle decreases, the amount of lateral force demanded from the tires also decreases.
The risk of understeer therefore becomes smaller.
Taken to the extreme, when steering angle reaches zero and the car is travelling straight, there is no longer any cornering demand in the idealized model.
That is why full-throttle acceleration becomes easiest when the steering wheel has returned to center.
The same principle applies to the rear tires.
The greater the steering angle and the greater the lateral acceleration, the more rear-tire grip must be devoted to resisting sideways motion.
As the driver unwinds the steering, less of the rear tires’ grip is needed laterally and more becomes available for acceleration.
This is why steering angle and throttle opening are so closely connected during corner exit.
Drifting: Inefficient for Lap Time, but Useful for Learning
If acceleration transfers too much load away from the front tires, the front axle may no longer generate enough lateral force to maintain the intended line. Understeer then appears.
At the same time, if excessive throttle causes the rear tires to exceed their available grip, the rear begins to slide and oversteer develops.
A drift can therefore be viewed, in one simplified sense, as a condition in which front and rear slip occur simultaneously.
The front tires are not following the intended steering path perfectly, while the rear tires are also sliding sideways.
The car’s heading, its direction of travel, and the direction in which the tires are pointing are no longer identical.
From a pure time-attack perspective, this is generally inefficient.
Energy is being spent on tire slip rather than producing the cleanest possible acceleration along the desired racing line.
But drifting can still be extremely valuable as a training exercise.
A driver who becomes comfortable controlling a car beyond the normal grip limit can develop a much clearer understanding of weight transfer, tire slip, yaw, throttle control, and recovery from oversteer.
That experience can make it easier to approach the limit confidently during conventional grip driving.
Conclusion: Understanding the Rear Tires Changes How You Corner
The ideal corner exit is reached when several things come together.
The car’s direction of travel aligns with the straight ahead. The vehicle’s momentum is travelling in the same direction. The front and rear wheels are effectively straight, with steering angle approaching zero.
At that point, the front tires no longer need substantial lateral grip, while acceleration has transferred load rearward and increased the traction available at the driven rear tires.
The driver can therefore apply maximum throttle without having to fight significant understeer or oversteer.
Zero steering angle, vehicle momentum aligned with the road ahead, and strong rear-axle loading create the conditions for the strongest possible corner exit.
In this article, I have looked at rear-tire grip as something that must continuously be shared between lateral stability and acceleration, while longitudinal weight transfer changes how much grip is available.
Lateral weight transfer, differential behavior, and the distribution of traction between the inside and outside tires add another layer to the discussion, so I will leave those subjects for another article.
The common phrase “turning the car with the differential” may ultimately be understood as an applied result of these interactions between lateral load transfer and traction distribution.
That is enough armchair theorizing for today.
