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Overview of Spur Gears – Everything You need to Know

In their most simple form, a spur gear is a circular steel disc with teeth around the perimeter.  Spur gears are probably the most common gears. These teeth work in conjunction with other gears to create a rotation.  The “toothed” edges cause these gears to look like a spur on the back of a cowboy’s boots. The gears are mounted on shafts that stand parallel to another, and this allows the spur of the first gear to interlock with the spurs of the second and create a rotation.

Spur gears are used in many industries, from the tiny spur gears in an analog watch, to the complex assortment in a car or aircraft engine, and up to the mechanics behind the world famous Big Ben in London.  Spur gears are all around us.

Definitions and Terms Associated with Spur Gears

Ratio: the ratio is determined by the number of teeth in a pair of gears.  For example, a 2:1 ratio exists if a device contains two gears, and one gear has two times the teeth of the other.  

Gear Trains: gear trains are made of multiple gears. Gears run together in multiple sets to reduce or increase the speed of the drive.

Gear reduction: this is an arrangement of gears in which the speed can be lowered for a slower output.

What Does A Spur Gear Do? 


As mentioned earlier, spur gears are used in a myriad of industries, and at IPG we manufacture a wide range of spur gear types and sizes for various industries including agriculture, automotive, automation, robotic, food processing, and 3D printer equipment, just to name a few.

Anywhere you see a motor or some type of rotation, there are likely spur gears involved. Common applications for spur gears are to increase or decrease the speed of the rotation, to reverse the direction of the rotation, to maintain a synchronized rotation between two axes, and to move rotational movement from one axis to another.

Understanding the concept of the gear ratio mentioned before is important.  If one gear is spinning at a rate that is twice as fast as the second gear, this is a result of the ratio between the gears.  In the example given above, if the diameter (the measurement from one side of the gear straight across to the other) is twice the size of the diameter of the second gear, then this is a 2:1 gear ratio.  The industry calls this a “two to one.”  In application, what this means is that each time the larger gear makes a full rotation around once, the smaller gear makes a full rotation around twice. [1]

How Spur Gears Help Alter Operating Speeds

If both gears had the same diameter, they would rotate at the same speed but in opposite directions. However, to increase or decrease speed, gears are often connected together in gear trains.

In a gear train, multiple gears of various ratios are joined together. Each gear turns at a higher rate than the gear before it.  This enables rotations in your designated time to increase at incredible speeds in a relatively simple process. 

For example, in the diagram below, four gears are in a gear train. In this gear train, the smaller gears are one-fifth the size of the larger gears. So, if you connect the second gear to a motor (1st gear) spinning at 100 revolutions per minute (rpm), the third gear will turn at a rate of 500 rpm and the last and smallest gear will turn at a rate of 2,500 rpm. Similarly, you could attach a 2,500-rpm motor to the smallest and last gear to get 100 rpm on the second gear. [2]

Advantages of Spur Gears

Spur gears have many advantages across applications.  The teeth provide the power behind mechanical processes we depend upon.  The teeth, often made of steel or other durable metals, prevent slippage between the multiple gears. This creates synchronization of the axles and the gears which are connected to each other.

Another advantage of the spur gear is they make it possible to know precise gear ratios. This occurs by counting the number of teeth in the two gears and then dividing the number.  For example, if one gear has 80 teeth and another has 20 teeth, the gear ratio between these two gears when they are connected to each other is 4:1.

Another very helpful advantage of spur gears is that they make it so minute imperfections in the measurements (diameter and circumference) of two gears do not cause major trouble. The gear ratio is still controlled by the number of teeth even if the measurements of the two gears are a slight amount off.

Disadvantages of Spur Gears

There are some disadvantages to spur gears.  The teeth endure stress, they cannot transfer power or energy over long distances, they are typically very noisy, and they require parallel axes to function. [3]

IPG’s Superior Customization Capabilities

Our goal at Illinois Pulley & Gear is to provide you with professional, high-quality, reliable services.  We manufacture a large variety of high-quality, made on demand, timing pulley stock and all the necessary spur gears. We are virtually unlimited in the variety of services we can provide from gears to your full-functioning pulley system.  IPG can produce stock or made-to-order timing pulleys with any of the tooth profiles listed here. Note: HTD, GT, and GT2 are registered trademarks of the Gates Mectrol Corporation.

We want to be your go-to resource for all of your customization needs, and we want you to have the peace of mind that your projects are in good hands.  Click here to contact us with more information about our complete offerings or to receive a quote for your next project.




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    Eric BroseProject Manager, Technico Precision Manufacturing, Inc.
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