Why does a car downshift when going downhill? Should we select high gear or low gear when going downhill?

It is very common for a car to go uphill or downhill. In fact, it is necessary to shift gears regardless of whether it is going uphill or downhill, so that the vehicle will not slide randomly. So why do cars need to downshift when going downhill?

Why does a car downshift when going downhill?

Whether it is automatic or manual, when going downhill, you need to downshift to the appropriate gear position, and you can control the vehicle's deceleration by reducing the throttle. The principle behind this is to let the resistance of the engine when reducing the throttle act on the wheels, so that the wheels also have resistance.

If it is a long downhill slope, we cannot actually use the brakes all the time, but we have to use the engine to brake. Engine braking is to shift the car's gear to a lower gear, and then slow down the car by reducing the throttle. This is equivalent to converting the gravitational potential energy of the car going downhill into a force that pushes the engine back.

When going downhill, should I shift into high gear or low gear?

Regardless of whether the car is manual or automatic, use low gear when going downhill.

From the transmission ratio principle, the gearbox has the strongest deceleration effect on the engine when in low gear, which is equivalent to amplifying the power of the car. Conversely, if the wheels act on the engine, low gear can also amplify the resistance of the engine, so that the resistance of the engine's own oil intake can be used to restrict the operation of the car's wheels. If the high gear is engaged, the power of the engine will be reduced, so the braking force of the engine will also be reduced.

For manual transmission cars, you can directly shift the gear to low gear. For automatic transmission cars, you need to use the manual-automatic mode to force the gear down. If some cars are not manual-automatic, you need to shift the gear to the low gear after D gear to allow the engine to brake to the greatest extent.

What to do if the car is not easy to shift into gear

Gearbox Problems

The transmission oil needs to be replaced regularly. If it has not been inspected for a long time, the hinged part of the gear shifting mechanism will be seriously worn, and there will be a deviation from the gear position of the gear shifting mechanism, resulting in the gear shifting failure. You can feel it is very difficult to shift the gear by pressing the clutch. In this case, just adjust the gear shifting mechanism.

Clutch Problems

It may be that the clutch is not completely disengaged, resulting in the inability to shift gears. Just go to a repair shop to adjust the separation stroke. Or the clutch pressure plate may have been deformed over time. Just replace it with a good quality pressure plate.