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12. Cassettes #4004 . Top
See Cassette Database for list of cassettes.
See the detailed part document titled Cassettes for even more detail.
What is a cassette? It is the cluster of gears on your rear wheel. The term "cassette" refers to the way the cassette slides onto the hub. The original 10 speed bicycles in 1970 up until the 1990s did not have cassettes, they had what was called a "freewheel" which screwed onto the rear hub. My 1986 Miyata 1000 still has this system. These "freewheels" contained not only the cogs but the bearings and ratchet mechanism. (Hence the word "freewheel as opposed to a fixed cog). But in the 1990's Shimano developed a new system called Uniglide whereby the cogs were a separate part. The bearings were now in a core hub which they called the "free hub". Note the term "Free hub" as comared with "free wheel". With uniglide each cog was a separate piece, and you could replace just one cog. But then to improve shifting they developed a system called "Hyperglide" with tiny ramps on each cog to the next cog. these cogs were sold as a matched set, and people replace the whole set. These cog sets are called "cassettes". With the cassette system I've never heard of anybody replacing individual cogs. The cogs are not sold separately, and even if they were, the argument is usually that the whole cassette needs replacement.
Over the years there was a gradual increase in the number of cogs on the back. The original 5 speed freewheel was replaced with 6 speeds. By the time uniglide came out, 6 was the standard. Then the cassettes started having 7 speeds, then 8, 9,10 and even 11! These extra gears were squeezed in first by increasing the "dishing" on the rear wheel (which made it weaker), and then by increasing the width of the dropouts from 126mm to 130mm and finally 135mm. To go from 7 speeds to 8, they made the chain slightly narrower (7.3mm to 7.1mm). But you could still use one of these 7-8 speed chains with any cassette. But to go to 9, and beyond, each time they had to make the chain narrower and the cogs thinner. Above 8 speeds, each number of cogs has a special chain. All this adds expense to the manufacture, and adjustments more fiddlesome. And they wear out faster.
Fortunately new bikes are still available with 7 and 8 speed cassettes. For example, most of the new bikes at Bike Doctor are 7 and 8 speed, with a few 9 speeds sprinkled in. And the 7 and 8 speed cassettes are widely available from multiple manufacturers, so the parts aren't going to get hard to find. (In fact you can still easily buy old freewheels which is what I have to do with my Miyata!
If buying a new bike, keep in mind that maintenance costs will be substantially less if you have 7 or 8 speeds. As I mentioned, the highest recurring cost of operating a bike are drive train costs. On my current bike, I'm using a $12 KMC chain and a $16 cassette, and they work perfectly.
- Max 8 Speeds
You can cut the costs substantially if you use 7 or 8 speed cassettes rather than 9, 10 or 11 speed cassettes. With 3 chain rings up front, you don't need more than 8 sprockets on the back. The problem with the 9, 10 and 11 speed cassettes is that the cogs are spaced increasingly closer together, and so the chains have to be narrower and everything is more likely to going out of adjustment.
Not only are the replacement cassettes less expensive, the chains are also less expensive. 7-8 speed chains can be removed for cleaning by a reusable master link, whereas 9 speed chains and above you must replace the master link each time. And the 8 speed cassettes last longer because the teeth can be wider.
- Replacing chains
Chains wear out faster than cassettes, and running a worn chain eats into the cassettes. See separate chapter on chains.
- Replacing Cassettes
To replace a typical 7 or 8 speed Shimano cassette, you need to remove the lock ring. It's really simple once you know how. There are lots of videos, all you need is a cassette puller, a big wrench and a chain whip. On my bikes, I'm using cassettes that are $28 or less, and chains that cost $14 or less. So my drive train costs are reduced to less than $50/year.
- Friction Shifters
All bikes before 1990 had simple friction shifters instead of indexed shifters. A friction shifter is just a lever held in place by friction. It doesn't click into gears, it just smoothly moves the chain left and right. They work with every cassette. You just move the lever till the chain goes up to the next gear. They never need adjustment because there is no adjustment. And they never change even if you change from 7 to 8 speed. Unfortunately, they are no longer mainstream. Instead, all new bikes have systems like Rapid Fire shifters which integrate both the brake lever and the shifter. And they have no friction mode. And if they are out of adjustment, most people need to get a mechanic to adjust them. All my bikes have friction shifters on them.
To eliminate adjustment hassles, use friction shifters rather than indexed shifters. Some index shifters have a friction mode. An indexed shifter is tied to a certain number of cogs, and a certain cog spacing. So a 9 speed shifter won't work on an 8 speed cassette. But friction shifters work on whatever cassette you want. And never need tricky adjustments.
- Big Sprockets last longer
Over the past decades, the industry has kept reducing the number of teeth on both front chainring and rear sprockets. The old 10 speed standard was 52 teeth on the front, and the smallest on the back was 14 teeth. But now the typical front chainring is around 38 teeth, and back cassettes have as few as 11 teeth. For the same 2:1 gear ratio, 52 teeth running on a 26 tooth rear will last way longer than 30:15. The reason is that with bigger sprockets, there is much less force required in the chain to transmit a given amount of torque. Furthermore the force is spread over more teeth and the chain bends less with each revolution. And worse still, the chain side plates and bearings are thinner. It all adds up exponentially to greatly increased wear. When riding, try to pedal in the largest pair of sprockets, so I shift to the large one whenever possible. The chain ring you wear out is usually the middle one.
- Is Derailleur specific
If you decide to downgrade a bike from 9 speed to 8 speed, will you have deraileur problems. The answer is no. The indexing is controlled by the shift levers not the deraileur. So you will need to change the shift levers if you downgrade. Or use friction shift.