Gears & Gadgets: Cassette Replacement
By David Cohen, Maryland National Capital Park Police Reserve Unit
It has happened to all of us at some point: The chain on our bike is skipping, jumping, or perhaps has snapped completely. So, we replace the chain with a new one, only to find that the new chain doesn’t make much of an improvement. Why didn’t the chain replacement work? The answer lies on the rear wheel; specifically, the rear cassette.
When replacing automobile tires, it is almost always recommended that an alignment be done as well. The alignment is performed so that the new tires will wear evenly. Putting new tires on a car that is out of alignment will result in a poor driving experience and premature wear of the tires. The same can be said about the relationship between the chain and the cassette. When replacing the chain, the cassette should also be replaced to avoid a poor riding experience and premature wear of the new chain.
When purchasing a new cassette, the first thing is to make sure that the gear range matches the existing cassette on the bike. This is done by counting the gear teeth. If you don’t know the number of teeth, then it’s a matter of counting them by hand. Mark one of the teeth with a Sharpie®, crayon, or piece of tape and count your way around. Most 9- and 10-speed cassettes are going to be 11 (smallest) to 34 teeth (largest), and the gear ranges. Once you start getting into single-ring front cranks, the gear ranges on 11- through 13-speed cassettes can be 9 (smallest) to 53 (largest).
(Theoretically, it is possible to change the rear cassette ratios. However, the other factors involved in making such a change, including chain length and derailleur clearance, are beyond the scope of this article and may be covered in a future G&G).
Once you have ascertained the proper gear range, the next step is to purchase the cassette. There is a dizzying array of bike parts manufacturers, and multiple models per manufacturer. The “big two” are Shimano and SRAM. The chief difference between the various model lines is usually weight. Lighter doesn’t always translate to better for the public safety role. The ¼ pound (.45 kg) you may save going with a premium cassette will barely be perceptible on a fully laden public safety bike; for the price of a premium cassette, you could buy several mid-level cassettes. Likewise, the “consumer grade” parts, like the Shimano ALIVIO line, are not going to hold up to the demands put on a public safety bike. A good balance can be found in the mid-level price lines: reliable enough to handle the rigors of public safety cycling without blowing the entire maintenance budget on a single component. My personal preference is the SRAM 970 line for 9-speed cassettes. They run around $45.
Replacement of the cassette is not a difficult operation. Two tools are required: A lockring tool and a chain whip. The lockring tool is needed to remove the cassette. The tool comes either with or without a guide pin. The guide pin goes into the hole for the quick-release through-axle. I personally prefer the lockring tool with a guide pin, but if you have bikes with different sizes of through-axles, you may want to purchase one without a guide pin. The chain whip holds the cassette in place while you loosen the lockring. The lockring tool is usually less than $10, and chain whips are typically under $30. A good quality tool will give you many years of service, so don’t try to find the cheapest one around.
To remove the cassette, remove the rear wheel from the bicycle. Remove the quick-release skewer and set it aside. Place the lockring tool into the splines for the cassette lockring. They should fit snugly and the tool should be more or less flush with the cassette surface once fully inserted. It is at this point you will discover the need for the chain whip. If you try to loosen the lockring without holding the cassette in place, the cassette will simply spin freely.
The chain whip should be placed on the cassette to hold it in place. Place a wrench on the lockring tool so that the lockring tool and the wrench more or less form a “V”. Turn the wrench counter-clockwise, while pushing the chainring tool clockwise to put pressure on the cassette. The lockring should release with a little bit of force. If it isn’t turning, spray the lockring with some PB Blaster or Seafoam DeepCreep. If those fail to release the lockring, it may be best to take the wheel to a local bike shop.
Once the lockring is off, the old cassette should come off fairly easily. If it doesn’t, a thwack with a rubber mallet on the rear of the cassette will usually do the trick. Once removed, there really is no need to keep a worn cassette, except as maybe a paperweight.
Before mounting a new cassette, clean the old grease off the freehub and apply a new layer of grease. This will not only make it easier to mount the new cassette, but it will also ensure that when it is time to replace this cassette, it will come off the freehub easily. As you apply grease to the freehub, you will see several splines on the hub. One of the splines is much narrower than the rest. Set this spline to the 12 o’clock position, as this will be the guide to mount the new cassette.
Remove the new cassette from its box. When you look at the rear of the cassette, you will notice one of the grooves is smaller than the rest. This is the groove which will line up to mount on the freehub. Take some grease and apply it to the inside of the cassette with your finger. Line up the narrowest spline with the narrowest groove and press the cassette on. Sometimes, the smallest chainrings are separate, so go ahead and line those up as you would with the larger part of the cassette.
With the entire cassette now mounted, apply a little bit of grease to the new lockring supplied with the cassette. Remember the lockring tool? You will need that to tighten down the lockring. Place the lockring tool into the splines of the new lockring. Some chain whip tools have the fitting for the lockring tool on the opposite end, but an adjustable wrench works fine, too. Tighten the lockring until it no longer moves easily. Do not over-torque the lockring.
The cassette is now mounted. Replace the quick-release skewer and mount the wheel back on the bicycle. With the wheel and new cassette on the bike, install a new chain. Once the chain is installed, the bicycle’s driveline may need a little bit of breaking-in before it achieves optimum smoothness. If the driveline continues to be problematic after the break-in period, the derailleurs may need an indexing adjustment by turning the barrel connectors. Once all is properly adjusted, a new chain and cassette will yield lots of miles of smooth and consistent service.
Gears & Gadgets is a blog written by David Cohen #1116. It features various repair tips and tricks that David has picked up in nearly 25 years of cycling, including 12 years of public safety cycling. Gears & Gadgets will also periodically review some of the latest “gadget” items of potential interest to public safety cyclists. The advice and opinions in this column are solely the author’s and should not be interpreted as IPMBA mandates or recommendations unless explicitly stated.
About the author: David Cohen is a 12-year volunteer with the Maryland-National Capital Park Police. When he isn’t riding or tinkering with bicycles, David can be found tinkering with vintage cars or World War II airplanes. An avid historian, David enjoys researching and writing as well. He can be reached at onyxsax@aol.com.
Photos courtesy David Cohen.