These are the two basic solutions if you want a few (or a dozen) sprockets and an external derailleur on the rear. Virtually everything except price speaks for a cassette, which I'll explain in the following paragraphs. However, it's worth clearing up a particularly vexing terminology issue first. It just so happens that in the cycling world, the word " freewheel " means two things. The first is a freewheel mechanism, which is generally found on every bike other than a fixed-gear bike. Therefore, it's also present in the hub for the cassette. Today, we'll be discussing a set of multiple sprockets permanently connected to this mechanism and threaded onto the hub, compared to the newer solution, the cassette. In this case, the "freewheel" mechanism is located in the hub, not the sprockets, which, as you'll soon discover, has many advantages.
As an aside, the word "sprocket" actually refers to a toothed rack that engages the wheels. The correct term would be "chain wheel" or "sprocket." However, I feel it's too late for a reform and would only cause unnecessary confusion. Let it be.
How is a freewheel constructed?
The sprocket assembly is mounted on a common frame (usually riveted). A ratchet mechanism is built inside, allowing you to stop pedaling. The whole thing is screwed onto the threaded hub with a special wrench. It sounds reasonable, so what's the problem? The freewheel width. The ratchet mechanism has a smaller diameter than the hub bearing, so a significant portion of the assembly protrudes beyond the hub body. While this wasn't a major problem with five-speed drivetrains, the more gears there are, the greater the leverage built into the smallest sprockets.
The first problem is precision – the lack of support combined with poor workmanship results in wobbling and noise. More noticeable to the average user, however, is the frequent occurrence of axle breakage, especially in quick-release models. For this reason, freewheels with more than seven speeds are rarely used (and even those tend to snap the axle). This problem is common in children's and youth bikes, where cheap freewheels (cost, cost) meet a real challenge. I've experienced this myself. The only upside is that repairs are very inexpensive.
It is worth noting that this problem does not occur in single-speed freewheels, where everything works on one axis.
Cassette is better
It's a wonderfully simple and logical solution. The ratchet mechanism has been moved to the hub, allowing it to be placed on the inside of the right bearing. This component is called the freehub. For hubs designed for heavier applications, additional bearings can be installed to distribute the load more evenly. Axle breakage is practically non-existent in typical recreational use. You can also confidently increase the number of gears and experiment with new freewheel mechanisms. My favorite is the Ratchet from DT Swiss. The cassette itself is a system of sprockets, usually placed separately, or in the case of larger ones, several placed on brackets. This allows for individual replacement of the smallest sprockets, which wear out the fastest. Furthermore, considering the price of 11- and 12-speed cassettes, separating them from the ratchet mechanism saves costs if one of them wears out.
The downside? Price, of course, although in the case of 7- and 8-speed drivetrains, where cassettes can be considered competitive, the cost difference is around 100-200 PLN. It's definitely worth paying extra. It's also worth mentioning the explosion of standards typical of bicycles, related to increasing the number of gears, decreasing sprockets, and, of course, competition. Sometimes, changing the drivetrain requires replacing the freehub, or even the entire hub. We write about choosing the right sprocket on our blog here.
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