We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is an Idler Gear?

By Benjamin R. Kibbey
Updated May 17, 2024
Our promise to you
About Mechanics is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At About Mechanics, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

When two gears are directly next to one another, they move in opposite directions to create motion. When both gears need to move in the same direction, an idler gear is used between the two. It transfers motion from one gear to the other while affecting nothing other than the direction in which the second gear spins. The gears the idler connects may be referred to as the "driving gear," which imparts motion, and the "driven gear," which accepts motion. The gear ratio between the driving and driven gears is calculated in the same manner as it would be were the idler gear not present.

Idler gears can also be used to create space between the driven and driving gears, as well as between the shafts that attach to those gears. In such a situation, the size of the idler gear will not affect the speed at which the driven gear spins, so the size of the idler gear can be determined simply by the space to be bridged. Such a configuration can also be set up when the use of larger driving and driven gears is impractical or impossible because of space constraints. In this manner, the idler may be used to achieve the same results as a belt or chain strung between the driving and driven gears.

Multiple idler gears may also be used to span a gap, paying attention only to their number so the driven gear spins in the desired direction. An odd number of idlers will cause the driving and driven gears to spin in the same direction, and an even number will cause them to spin in opposite directions. This method also may be employed to connect driving and driven gears when there is a physical obstruction that would prevent them from making direct contact. This is accomplished by arranging a series of idlers so they go around the obstruction.

In the case of a manual vehicle transmission, the reverse idler allows the shaft that drives the forward gears to also drive the gear that propels the vehicle in reverse. All the other gears in the transmission make direct contact with the countergear, the gear that allows the transfer of power to the axle that moves the wheels and, in turn, moves the vehicle forward. The reverse gear, however, has the reverse idler gear between it and the countergear. The presence of an idler gear between the reverse gear and the countergear causes the axle and wheels to spin in a different direction than they do when the other gears are engaged, propelling the vehicle in reverse. The term "reverse idler gear" may also be used to simply refer to a single idler in any scenario.

About Mechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.

About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.