Exited the corner, encountered a clear road and tossed into the higher gear because you wanted to speed up. But do you have an idea what actually happens when you shift up or down through the gears? Plenty of fellows out there know how to handle the gear stick of their cars and when to shift through the gears but alas, understanding the interesting mechanism going on behind the scenes isn’t their cup of cake. And for the ones, including me, who haven’t ever had the opportunity to drive a car, it takes a hell lot of time and effort delving into the science behind the working of gears. You need to imagine yourself actually driving a car, encountering various road conditions like wet or dry, going up a hill or descending downwards, riding on a straight clear road or one with lots of turns and accordingly deciding which gear to shift into. Afterall, some things need to be learnt the hard way, for the mind comprehends them better that way. This blog is an attempt to make the concept of gear working mechanism crystal clear to the readers and here we go into it.
What’s this Gear Ratio???
First and foremost thing that needs to be understood is the “gear ratio”. Simply put, it is the ratio of the speed of the driving gear to the speed of the driven gear. In context to a car, it is analogous to the speed of the engine to the wheel speed. Now, this ratio is achieved with the help of a set of gears present inside the gearbox. The driver operates the gear stick, the gears mate with each other and the desired gear ratio is obtained. Also, regulating this ratio depends on various factors such as those in the aforementioned paragraph.
High and Low gears??!!!
Before going further into this, a confusion that needs to be made clear is that high gear means the ratio is low and low gear means the ratio is high. At lower gears the engine RPM is way too high than the wheel speed. It revs up to a great extent and generates a lot of power needed to push the car. Shifting into low gears is done when one needs to accelerate to attain a high speed. The wheels get much traction,i.e., grip from the road and this helps the car to accelerate. More the horsepower produced, more quickly a speed will be attained. Now once the car speeds up to the desired range, the driver shifts into a higher gear, gear in which the engine RPM lowers and the wheel speed elevates, opposite to that of a lower gear.
Still confused? An analogy always works…
Imagine you have a large heavy ball that you need to roll on a leveled surface. At first, you will put a lot of effort to start rolling the ball, much force required for that. But once it starts rolling, you need to apply just a little force to keep it moving on. Moreover, it will speed up if you push it harder. Similar is the connection of engine and wheel. At low gears, the engine revs up a lot, generating a lot of power to start moving the car but once the car accelerates and the desired speed is attained, a higher gear is shifted into, the engine now revs relatively less or puts a little effort to maintain that vehicle speed.
So what’s the thumb rule? Gear up when the speed of your car increases and gear down when you need more power from the engine. And, shifting up or down through the gears will depend on how much you want to accelerate or how much cruising speed you desire. Other than working on the gear stick to shift gears, some other mechanisms too need to be worked upon. What are they? The clutch pedal, brake pedal and accelerator pedal.
Now, what will you do if you are driving at a considerably safe high speed and encounter an obstacle at a distance? Your first instinct will be to apply the brakes. That’s correct. Next? To shift down a few gears so that you’ll accelerate again once past the obstacle? This isn’t a feasible decision to take unless the speed of your car was way too high and the obstacle you encountered showed up all of a sudden. The better choice would be to just brake down to a considerable speed and release it once past the obstacle to regain the original speed. You need not always gear down in such situations. Downshift only when you need to accelerate to an even higher speed than before.
So at this point you would have got a pretty much good idea about when to shift gears and what shifting into high and low gears actually means. Consider two types of roads: one is a straight clear road and another with lots of turns.
Think which gears will be most used when driving in either of the two situations? Of course, when driving on the former, you’ll wish to just speed up your car and hence, shift into a higher gear that will provide you a cruising speed. Now with the latter road, you will hardly get to use the higher gears unless you wish to crash your car and make your day into the hospital. When entering a corner, you’ll apply the brakes, and when exiting it, you’ll downshift to speed up a bit and then again repeat the same when another turn comes ahead. Really a tiring ride.
Low gears are used most often in heavy vehicles since the engine needs to produce a lot of power to push such vehicles. Same is the case when riding your way up through a hill or when your car wheels sink a bit in a muddy road and you need to get them out. In contrast, high gears are beneficial when top speed performance is desired. Downshift, press the accelerator pedal, speed up and then shift up to maintain the cruising speed.
But what about the fuel efficiency???
Now after all this talk about gear shifts, one important aspect that needs to be highlighted is the fuel efficiency. When in a lower gear, since the engine revs up a lot to produce great power, much amount of fuel is consumed. In contrast, the engine doesn’t work as much at higher gears and hence, the fuel consumption goes down and efficiency improves. Eventually, the benefit of a large horsepower generation comes at the expense of burning a lot of fuel. But horsepower is what sells cars today so fuel efficiency will have to be compromised with anyhow.
An Adventure in Science 