What do gear ratios mean

Transmissions are some of the best examples of the practical applications of gear ratios. Anyone who has ridden in a car or other motorized vehicle has benefited from transmissions in some form. And every transmission is essentially just a bunch of gears and gear ratios packed closely together. Take a look at the incredibly helpful video from Learn Engineering below to learn more about how manual transmissions work.

It's important to note that while manual transmissions are falling out of favor with automakers, as they are not easy to incorporate in hybrid or electric vehicles , they function almost identically to how automatic transmissions work, as far as gearing goes. The main difference is in how the gears are shifted. Manual transmissions will involve action by the user moving the gear shift and clutch to shift, whereas automatic transmissions will use input from the car's onboard computer or, in very early models, mechanical input from either the car's speed or the car's engine.

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Join Our Free Trial Now! Learn More About gear ratio. Statistics for gear ratio Look-up Popularity. Style: MLA. Get Word of the Day daily email! Test Your Vocabulary. Test your vocabulary with our question quiz! Need even more definitions? Let's say you want a gear ratio of One way to create that ratio is with the following three-gear train: In this train, the red gear has three times the diameter of the yellow gear, and the blue gear has two times the diameter of the red gear giving a ratio.

However, imagine that you want the axis of the output gear to be the same as that of the input gear. A common place to need this same-axis capability is in an electric screwdriver.

In that case, you can use a planetary gear system, as shown here: In this gear system, the yellow gear engages all three red gears simultaneously. They are all three attached to a plate, and they engage the inside of the blue gear instead of the outside. Because there are three red gears instead of one, this gear train is extremely rugged. The ouput shaft is taken from the plate, and the blue gear is held stationary. You can see a picture of an two-stage planetary gear system on the electric screwdriver page.

Finally, imagine the following situation: you have two red gears that you want to keep synchronized, but they are some distance apart. You can place a big gear between them if you want them to have the same directions of rotation:.

However, in both of these cases the extra gears are likely to be heavy and you need to create axles for them. In these cases the common solution is to use either a chain or a toothed belt , as shown here:. The advantages of chains and belts are light weight, the ability to separate the two gears by some distance, and the ability to connect many gears together on the same chain or belt. For example, in a car engine, the same toothed belt might engage the crankshaft, two camshafts and the alternator.

If you had to use gears in place of the belt, it would be a lot harder! Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Under the Hood. How Gear Ratios Work. Gears are generally used for one of four different reasons: To reverse the direction of rotation To increase or decrease the speed of rotation To move rotational motion to a different axis To keep the rotation of two axis synchronized You can see effects 1, 2 and 3 in the figure above.

Understanding the concept of the gear ratio Understanding the concept of the gear ratio is easy if you understand the concept of the circumference of a circle. Gear Trains To create large gear ratios, gears are often connected together in gear trains , as shown here: The right-hand purple gear in the train is actually made in two parts, as shown. Gear trains often consist of multiple gears in the train, as shown in the following two figures: In the case above, the purple gear turns at a rate twice that of the blue gear.

The gear train shown below has a higher gear ratio: In this train, the smaller gears are one-fifth the size of the larger gears. Other Uses for Gears There are many other ways to use gears. An Example Finally, imagine the following situation: you have two red gears that you want to keep synchronized, but they are some distance apart.