This is a question that has plagued me for years... what's the difference between a cassette and a freewheel? In fact, I commonly refer to any cluster of sprockets mounted to the rear wheel of a bicycle as a "cassette" in my review videos.
The original bicycles had no chain and the crank arms were connected to the front wheel! But, the second iteration used a chain to spin the rear wheel, so the front wheel could be turned for steering. That rear wheel used a single sprocket, much like a children's bicycle of today (with coaster brake, where you backpedal to brake). Then, as more gears were introduced over time, to make starting and climbing easier, a part called a freewheel was crated that could "free wheel" as the cyclist stopped pedaling. This allowed people to take a break and even pedal backwards! Instead of designing this mechanism as part of the wheel, it was introduced as an inner core on the cluster of gears, but this limited how small the smallest sprocket could be. The free-wheeling core required space for bearings inside. A second limitation to this original freewheel design was that the axle going through the hub of the bike wheel was not supported as far out as the cassette was mounted... and the problem only got worse as hub spacing designs got wider! You see, the bearings mating the axle and wheel hub (where the spokes connect) were close to the center of the axle, and this meant that the axle could break more easily than if they were spread out towards the ends of the axle.
Eventually, manufacturers designed a way for the free-wheeling core to mate with a longer wheel hub with bearings that were spaced out futher. This is called the freehub body. This core interfaces with a cassette of sprockets, that slide down a track of splines. There are several standards for these freehub body parts that allow for 11 and even 10 tooth sprockets (SRAM XD Drive and Shimano Micro Spline are the new smaller freehub body products). These smaller sprockets function as your "high gear" when riding a bicycle, allowing you to pedal comfortably at high speeds and in fact to simply reach high speeds. At the end of the day, freehub body and cassettes are the best option for gear range options (up to 12 sprockets!) and wheel axle strength, but they do cost more than the old school freewheels... which is why we still see them from time to time on cheap electric bicycles.
In summary: a freehub is a part that threads onto the hub of a rear wheel of a bicycle. It holds a cluster of sprockets, or cassette as it’s commonly referred to. The freehub contains the drive mechanism that allows coasting and backpedaling on the drivetrain. The cassette slides onto the freehub body and is held in place by splines and then compacted securely in place by a lockring. Special tools are required to remove or attach the cassette to the freehub... which you can see on the ground during our conversation, but which we really don't talk about. Big thanks to Sean Lee at Rocky Cycles in Surrey British Columbia for sharing his parts and teaching me, so I could share back with you!
The original bicycles had no chain and the crank arms were connected to the front wheel! But, the second iteration used a chain to spin the rear wheel, so the front wheel could be turned for steering. That rear wheel used a single sprocket, much like a children's bicycle of today (with coaster brake, where you backpedal to brake). Then, as more gears were introduced over time, to make starting and climbing easier, a part called a freewheel was crated that could "free wheel" as the cyclist stopped pedaling. This allowed people to take a break and even pedal backwards! Instead of designing this mechanism as part of the wheel, it was introduced as an inner core on the cluster of gears, but this limited how small the smallest sprocket could be. The free-wheeling core required space for bearings inside. A second limitation to this original freewheel design was that the axle going through the hub of the bike wheel was not supported as far out as the cassette was mounted... and the problem only got worse as hub spacing designs got wider! You see, the bearings mating the axle and wheel hub (where the spokes connect) were close to the center of the axle, and this meant that the axle could break more easily than if they were spread out towards the ends of the axle.
Eventually, manufacturers designed a way for the free-wheeling core to mate with a longer wheel hub with bearings that were spaced out futher. This is called the freehub body. This core interfaces with a cassette of sprockets, that slide down a track of splines. There are several standards for these freehub body parts that allow for 11 and even 10 tooth sprockets (SRAM XD Drive and Shimano Micro Spline are the new smaller freehub body products). These smaller sprockets function as your "high gear" when riding a bicycle, allowing you to pedal comfortably at high speeds and in fact to simply reach high speeds. At the end of the day, freehub body and cassettes are the best option for gear range options (up to 12 sprockets!) and wheel axle strength, but they do cost more than the old school freewheels... which is why we still see them from time to time on cheap electric bicycles.
In summary: a freehub is a part that threads onto the hub of a rear wheel of a bicycle. It holds a cluster of sprockets, or cassette as it’s commonly referred to. The freehub contains the drive mechanism that allows coasting and backpedaling on the drivetrain. The cassette slides onto the freehub body and is held in place by splines and then compacted securely in place by a lockring. Special tools are required to remove or attach the cassette to the freehub... which you can see on the ground during our conversation, but which we really don't talk about. Big thanks to Sean Lee at Rocky Cycles in Surrey British Columbia for sharing his parts and teaching me, so I could share back with you!
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