Hub Engagement Designs – Part 1

Most of the bicycles come with an engagement system, which is almost always is an integral part of the rear wheel, or to be precise – of the rear hub. There are some exceptions – like track, or fixed gear hubs and trial bikes. The latter often employ the engagement system not as part of the hub, but of the bicycle frame and is integrated with a bottom bracket unit.

The purpose of the engagement system is to temporarily disconnect the drive system from the wheel. That is when a rider stops pedalling, the wheel continues to roll. This mode is also known as “coasting”. Technically, it enables the one-way power transmission from the cranks to the wheel. One-way means that the rotation motions is always transferred from the cranks to the wheel, and not the other way around. All engagement systems automatically switch between engaged and disengaged mode. The system disengages as soon as the rotational speed of the wheel and of the drive unit do not match. The drive unit, or rotor, on the most road and MTB bikes is commonly referred as the freehub. It mounts the sprocket or cassette and receives the rotational motion from the cranks.

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