When a driver presses the gas and brake pedals at the same time, the following happens: the engine starts to increase RPM, transmitting increased torque to the wheels, but the braking system at this moment holds back the rotation of the wheels, preventing them from spinning freely.
As a result, the greatest load falls on the parts responsible for transmitting torque.
A natural question arises: what does this threaten for the car and why is such a technique used at all?
We will not delve into the details of the gearbox design — we have already covered this issue in detail in the article «What will happen if... you engage reverse gear while moving forward», but it is obvious that for different types of transmissions the consequences will differ.
Manual transmission
In a car with a manual gearbox, the function of transmitting torque from the power unit to the gearbox is performed by the clutch, which provides a mechanical connection between the engine shaft and the manual gearbox shaft.
The principle of clutch operation is based on friction between two discs: one is fixed on the engine shaft, the second on the gearbox shaft.
When the clutch is depressed, the engine and gearbox are disconnected. When releasing the clutch pedal, the friction force between the discs gradually increases, and the rotation speed of the gearbox shaft begins to equalize with the engine shaft speed.
With the pedal fully released, both shafts rotate at the same speed.
So, if you press the gas and brake at the same time, the following happens:
- With increasing engine RPM, the engine shaft transmits increased torque to the manual gearbox shaft.
- Between the clutch discs, a difference in rotation speed arises and intensifies — slipping begins.
- A significant amount of thermal energy is released.
Simply put: if on a car with a manual gearbox you simultaneously hold the gas and brake pedals, the first thing to suffer will be the clutch — it will simply burn out. Other transmission components and the engine itself will also be under excessive load.
However, there is good news: most likely, the engine will stall before the clutch has time to completely fail.
Automatic transmission
In a car with an «automatic», the transmission of torque from the engine to the gearbox is taken over by the torque converter, which connects the elements through fluid.
The torque converter consists of three main parts: the pump wheel, the turbine wheel, and the reactor.
The pump wheel is rigidly connected to the torque converter housing. When the engine shaft rotates, it creates a flow of oil inside, which drives the turbine connected to the automatic transmission.
The reactor is designed to adjust oil flows: it increases torque when starting off and prevents the engine from stalling when stopping with a gear engaged.
So, if you press the gas and brake at the same time, the following happens:
- With increasing engine RPM, the pump wheel transmits greater torque to the turbine wheel connected to the automatic transmission.
- Between the two wheels, a difference in rotation speed appears and intensifies.
- The turbine wheel begins to «slip» relative to the pump wheel, accompanied by intense heat generation.
In other words: when simultaneously holding the gas and brake pedals on a car with an automatic gearbox, the first to fail will be the torque converter — it will burn out. Of course, other transmission elements will also experience increased loads.
However, the electronics of many modern cars can protect the vehicle from such abuse: if the brake is fully depressed, the automatic transmission simply locks.
Why do you need to press the gas and brake at the same time
Despite the serious consequences for the car, simultaneous pressing of both pedals is indeed used. But this is done rarely and only for a specific purpose.
On a manual gearbox, this technique is used to:
- redistribute weight between the axles of the car when overcoming uneven surfaces;
- maintain the required engine RPM during braking;
- cause a controlled skid.
It is not hard to guess that such techniques are available mainly to athletes, and it is best to use them on specially prepared cars.
But with an automatic transmission, pressing both pedals is used for testing the performance characteristics of the engine and gearbox. To do this, the brake is held, the engine is started, the automatic transmission is shifted to «drive» mode, and the accelerator is pressed. Then, based on the achieved engine RPM, diagnostics are carried out.
Summary
If you simultaneously hold the gas and brake pedals, the clutch or torque converter will burn out. In addition, other transmission elements may also suffer.
Dosed simultaneous pressing is used for sports purposes and for vehicle diagnostics.
To learn how to properly use all the capabilities of the car, long and persistent training is required. Therefore, without proper preparation, you should not press the gas and brake at the same time.
