Descent from a mountain pass or a protracted descent along the serpentine is a test not only for the nervous system of the driver, but also for all systems of the car. Many inexperienced drivers make the critical mistake of relying solely on the brake pedal, forgetting that the driver is not a driver. engine-braking It is the safest and most effective way to control speed in such conditions. Ignoring this principle can lead to overheating of brake pads and discs, which is fraught with a complete failure of the brake system at the most inopportune moment.
The basic principle of safe descent is that you should choose a gear that will allow the car to descend at a safe speed without constant pressure on the brake pedal. This means that before starting the descent, it is necessary to reduce the speed in advance and switch to a lower stage in the lower direction. gearbox or use manual modes in automatic transmission. The choice of the correct transfer depends on the steepness of the descent, the weight of the car, the condition of the road surface and weather conditions.
In this article, we will examine the physics of the process in detail, consider the features of the operation of various types of transmissions and give clear recommendations on how to avoid dangerous situations. It is critical to understand that on long descents, the brakes are only designed for short-term speed correction, and not for permanent car retention. Proper use of engine inertia will save you from expensive repairs and potential accidents.
Physics of the process: why the engine brakes better than the pads
When you release the gas pedal, the throttle closes, and the engine cylinders get a minimum amount of fuel-air mixture. However, the pistons continue to move, driven by the inertia of the car, and begin to compress the air in the cylinders. This creates a powerful resistance to the rotation of the crankshaft, which is transmitted through the transmission to the driving wheels. The lower the gear is selected, the higher the engine speed at the same speed, and the stronger the effect engine-braking.
Unlike friction brakes, which convert kinetic energy into heat by heating discs and pads, the engine dissipates this energy through the exhaust system and cooling system. This is a way to avoid it. heat-overload braking system. On protracted descents, lasting several kilometers, the constant operation of the brakes can lead to their "boiling" and the appearance of a steam plug in the brake fluid, which will instantly make the brake pedal "cotton" and ineffective.
⚠️ Warning: Never turn off gear or switch to neutral when descending! The coast down takes away control of the car and disables the engine braking, forcing you to rely only on brake pads, which in such conditions quickly overheat.
In addition, with the on transmission and released gas pedal, modern engine control systems completely block the fuel supply. The consumption at this point is zero, which also saves the car resources. In the first gear, the resistance is maximum, in the second - less, and so on.
Algorithm of actions for manual transmission (ICT)
For mechanic car owners, gear selection is a completely manual process that requires prior planning. Approaching the beginning of the descent, when the road is still horizontal or has an uplift, it is necessary to assess the steepness of the upcoming section. If the descent is steep and long, reset the speed in advance and switch to a gear that will provide engine speeds in the range of 3000-4000 rpm at the desired descent speed.
Often drivers mistakenly choose too high gear, hoping for silence in the cabin, but this leads to the fact that the car begins to accelerate under the influence of gravity, and you have to constantly slow down. If you feel that the car is gaining speed even in the gear on, you need to safely reduce the speed with the brake and switch to a step below. Switching to lower gear It must be made before the vehicle reaches dangerous speed.
☑️ Preparations for the IPC descent
When switching down at high speed, use the gas-gas-regasing technique to avoid breaking the wheels into the lock and damaging the clutch, although on the descent the speed is usually already low. If the descent is very steep, it may be necessary to turn on the first gear. Don’t be afraid of high revs: modern engines are able to work in the red zone of the tachometer for a short time without damage, while failed brakes are a direct path to an accident.
Features of descent on automatic transmission (ACP)
Owners of cars with classical hydrotransformer They often rely on the D mode (Drive), which is a mistake on steep descents. In this mode, the box tends to switch to higher gear for fuel economy, minimizing the braking effect. For safe descent, you need to transfer the selector to manual mode (designated as M, S or +/-) and force the lower gear to be selected.
Many modern cars have special modes for descent. For example, the regime L (Low) blocks switching above the first or second gear. Some SUVs are equipped with a system Hill Descent Control (HDC), which automatically brakes the wheels, but even then it is recommended to choose the lower gear manually so as not to overload the braking system with electronics. Switch the selector before the descent begins, while the car is on a flat surface.
| RIGUE RADIO | Description of the work | When to use on the descent |
|---|---|---|
D (Drive) |
Automatic selection of all transmissions | Only for gentle, short descents |
S / M (Sport/Manual) |
Manual control or shift delay | For moderate descents, fixation on 2-3 gears |
L / 1, 2 |
Lockdown on lower gears | For steep mountain slopes and off-road |
W (Winter) |
Touching from second gear | Not recommended for braking, just for start |
It is important to note that when switching to low gear at high speed, electronics can block the action to avoid damage to the engine or transmission. Therefore, reducing the speed before switching mode remains mandatory. It is also worth considering that hydrotransformer It can heat up with prolonged slippage at low gears, but this risk is not comparable to the risk of brake failure.
What to do if the transmission does not switch?
If the gearbox refuses to go manual or to lower gear on the move, this may be a protective feature. In this case, it is necessary to smoothly reduce the speed of the brake pedal to a minimum (20-30 km / h), stop, and only then switch the selector to L or 1 mode.
Variators (CVT) and robotic boxes: the nuances of control
Management variator On the descent, special attention is required. In normal mode, the variator seeks to maintain minimum engine speeds, simulating the highest gear, which completely removes the effect of braking. Owners of such vehicles categorically rely on mode D. You must use pseudotransmissions (stage imitation), if any, or mode L. Some models have an engine braking emulation function that needs to be activated separately.
Robotic boxes, such as DSG or AMTThey behave differently. Preselective robots (DSGs) in D mode can keep the transmission longer, but it is better to put them in sports mode S hand-held M. The peculiarity of robots is that they can quickly overheat with frequent switches and creeping mode, so choosing one fixed gear for the entire descent will be the best solution. This will reduce the wear of clutches and mechatronics.
When using a CVT, remember that it has no physical steps. When you select "first gear" in manual mode, you simply specify a program that holds a high transfer rate. The braking effect will be milder than on the mechanics, so control the speed more closely and use intermittent pedal braking for correction.
⚠️ On cars with a CVT, avoid long-term operation of the engine at extremely high revs (in the red zone) for more than 2-3 minutes, as the CVT cooling system may not cope with heat removal, which will lead to an emergency mode.
The impact of road conditions and all-wheel drive
The choice of transmission also depends on the coverage. On dry asphalt, you can use the maximum effect of braking the engine. However, on wet roads, rolled snow or gravel, a sharp engine braking (especially in first gear) can cause the driving wheels to lock. This will lead to skiding, especially on rear-wheel drive cars, or to the demolition of the front axle on front-wheel drive. In such conditions, you should choose a transfer one step higher than on dry asphalt.
For all-wheel drive owners (4WD or AWD) the situation is complicated by the transfer case. If you have a regimen 4L (lowered row), its use on extremely steep and slippery slopes greatly facilitates the task. The lowering row increases torque and enhances the effect of engine braking several times, allowing you to descend almost without using the brake pedal.
When descending on a slippery road (ice, snow, clay), try not to use the brake pedal at all, adjusting the speed only with gas and the choice of transmission, so as not to disrupt the car into a skid.
Stabilization systems (ESP, ABS) help to maintain the trajectory, but they are not a panacea. If the wheels are blocked due to too sharp braking by the engine on ice, the electronics may not have time to react. Therefore, on slippery slopes, act smoothly, without jerks, and keep a reserve of distance to the cars ahead.
Typical errors and their consequences
One of the most common mistakes is to try to “save fuel” by coasting on a neutral gear. Not only is it prohibited by traffic laws in many countries, it is also deadly. You lose the connection of the wheels with the engine, and the car turns into an unguided projectile that can accelerate to a speed at which the brakes can no longer stop it.
Another mistake is a late switch. The driver waits for the speed to rise, and then tries to plug the first gear. At high speed, this is impossible to do (electronics will not), and trying to turn on low gear on the mechanics can lead to a box breakage or instantaneous wheel locking. Always prepare for the descent in advance, at the top of the climb.
Drivers often ignore overheating signals. If you smell a burn or the brake pedal is softer, stop immediately in a safe place (if possible using natural obstacles or a detour) and let the brakes cool. Continuing to drive with overheated brakes is a direct risk of fire or system failure.
The main rule of mountain driving: the descent speed should be determined by the selected gear, and the brake pedal is used only for short-term correction or complete stop.
Frequently Asked Questions (FAQ)
Can the engine stop when braking on the descent?
On modern injection cars, it is almost impossible to stall when braking the engine, since the control system itself regulates the supply of fuel and air. However, on old carburetor machines or with a faulty idle regulator, this is possible. If the engine stalls, then the speed has fallen below critical, and you need to switch to a transmission below or add gas.
Is it harmful to the engine prolonged braking at high speeds?
Short-term operation of the engine in the red zone (up to 5-7 minutes) on the descent does not harm the engine. The cooling and lubrication system is designed for such loads. It is much more dangerous for the car to overheat and fail the brake system than the engine at high revs under load.
What to do if the brakes are missing on the descent?
Don't panic. Hold the steering wheel tight. Gradually, without jerking, switch gears down (with manual transmission) or use manual mode (ACP) to maximize the use of engine braking. Use a handhold (intermittently, without clamping to the end, so as not to block the rear wheels). Look for emergency truck exits or soft obstacles (snow, bush) to stop.
Do I need to warm up the engine before a steep descent?
It is not necessary to warm up the engine if the car is already warmed up after the trip. However, if you’ve just started a cold car at the foot of a mountain, let it work for a couple of minutes to let the oil spread through the system before you start moving up or down.