I have always wondered what those loud noises are the semi-trucks make as they appear to be slowing down, but I don’t understand how that helps?
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If you’ve ever ridden a 10- or 12-speed bicycle, those employ a similar concept as a transmission on a car. 1st speed is the biggest gear.
Bigger gears are better at producing torque (think more leverage, which equates to better ability to turn/twist). Smaller gears are better at producing speed. The difference with bicycles opposed to cars/trucks is that “ticka-ticka” sound when you’re not pedaling. That’s essentially the bike equivalent of coasting. It’s like being in neutral when you’re not pedaling.
Now take those concepts and apply them to a vehicle with a transmission that can be put in and taken out of gear manually, whether you’re trying to accelerate, slow down, or just maintain a consistent speed while going down a hill.
The tendency of a lower (larger) gear to want to create torque but not want to go as fast as the higher (smaller) gear works in both directions. If it’s engaged when you’re going slow and you hit the accelerator, it’s good at speeding you up. If you engage the low gear while you’re going faster and don’t hit the gas, the speed of the wheels will cause that gear to spin at a really high rev (hence the sound) until the weight of the engine being forced to turn without any fuel slows the vehicle to a speed that the gear “wants” to go.
Engine breaking is extremely important for driving in the mountains, and absolutely critical for large, heavy vehicles as it assists their brakes which tend to overheat and become molten mush when overused.
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