Why does the car’s reverse gear make more noise than other gears?

There are curiosities that, sooner or later, pop into everyone’s head, especially if they are part of everyday life. Even though you use it little, at very low speeds during parking maneuvers, you will have sometimes had to drive several meters in reverse gearor assist some other driver in the maneuver, and you will certainly have heard that the car does a noise very different from usual. If you have wondered why, the answer is quite simple, but it has to do with a component that few of us will ever have the opportunity to observe live…

car gearbox animated gif

It is in fact in the exchange that we find the reason for this noise: the difference comes from the different manufacturing method between normal gears and reverse gear.
The “forward” gears” are (in modern cars on the market) toothed helical: the teeth of the gears are i.e oblique and “curved” with respect to its axis of rotation. This allows simpler and more progressive insertionsone larger contact area between the teeth and less rubbing noise during rotation, ensuring quieter running and easier operation.

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The use of the gearbox is also aided by synchronizers. This is a component introduced in the 1960s, composed of 3 parts of which one is connected to the drive shaftone transmits the command from gear shift and the last one is a elastic ring which, taking advantage of thefrictionmanages to speed up or slow down the rotation of the gear to make it identical to that of the tree. Once the speed between the shaft and the gear is synchronized, with that characteristic “resistence” that we feel when pushing the gear shiftthe synchronizer rigidly connects the shaft and gear avoiding “grates”impacts between teeth in failed insertions which in the long run can damage our vehicle.

But let’s get back to ours back: why is it not the same as the rest of the exchange? Since he usually comes used for very short stretchesat low speeds and is normally always engaged with the vehicle stationarythe reverse gear is often cheaper to make, and is therefore a straight teeth.

Spur teeth gears

For this reason, its operation causes a greater noise and acute, which increases as the engine rpm increases and therefore as the “impacts” between the teeth increase: the engagement also leads to scratching more often, because in most cases it is also the only non-synchronized gear in our cars.

Last curiosity: the most car racing enthusiasts among you will have heard similar noises, especially in videos taken from the cockpit of cars modified by enthusiasts or in any case deriving from series models, even when the cars are moving forward.

In competitions gearboxes with straight tooth gears are often used, but the choice is not due (solely) to savings: in this case, these are preferred due to the less friction and therefore lower power losses. Another factor to the disadvantage of helical gears it’s “lateral” forces caused byinclination of the teethwhich in sporting use can damage the gearbox components if not properly designed.