Bicycle Mechanics - Newbie: Chain and Cassette Replacement

A couple years ago I bought the 2005 Original Discovery Channel Trek Team Bike (1 of 100 made apparently) on the recommendation of a friend who's brother rides professionally.

I've had it tuned a couple of times, but as a noob I have little knowledge in bike maintenance save for chaining tires, lubing chain, etc.

I've ridden the bike about 750 miles in the two years I've had it and recently took a bike maintenance class where we learned to measure the chain. The mechanic told me that mine needed replacing and that I should also replace the back cassette too.

The chain has never slipped on me.

Do I absolutely need to replace the cassette as well? How can I determine if I need to replace the cassette as well? How much is it going to run me? I would like to keep decent part on it, but don't want to spend a fortune (the mechanic mentioned that if I put anything better than "105s" on it I would probably be wasting my money)?

Thanks guys!

Matt in NYC

A worn chain wears the teeth on the chainrings , replacing the chain early,
extends the life of the chain-wheels it contacts.

As the only thing that chages from one steel cassette to another is the plating color

he's got it , the fancier stuff adds light weight but less durable materials , Al/Ti.

Chains are designed to wear down first, before other components such as chain rings and the cassette, but those can wear down too. With riding your pedaling motion is transferred to the wheel via your chain and cassette. All that torque stretches out the chain. I'm sure you learned that in your class. In some cases, orignal parts with wear down together fitting to each other like a hand and glove. Some times when you replace one of these 3 parts (chain, cassette, chainrings) things won't fit quite right. its like getting a glove too small for your hand. You'll notice grinding, and or poping, if you also need to replace your cassette. I would start with just getting the chain about $20 at any LBS. Wal-mart one-time-use tool is about $7 and for a LBs to do it is roughly $10 where I live. Replacing a chain is something you can do your self, you just need the tool and make the chain the right length. If you or the LBS notice a mis-match due to a worn cluster, you'll need to get the shop to do it, and cost of a new one depends on how many speeds you have.

It's difficult to predict whether a used cassette will work with a new chain, but you can make an educated guess based on how stretched the old chain is. If it's less than 1%, (1/8" over 12") the odds favor you, beyond 1% the odds decline quickly. I always start by replacing only the chain and see how things are. If it runs smoothly the cassette is fine, if not replace the cassette.

BTW- I'm surprised that your chain is toast after only 750 miles. Did you measure it with a 12" rule, or with a gadget. I ask because most of the gadgets sold tend to read high, and you might be tossing a chain with hundreds of miles of life still to go. Check again, then treat it to some decent chain lube and take it until it's stretched 1/2%, or 1/16" over 12, by ruler check.

Another thing to consider. You replace chains early in order to save the cassette. If the horse has already escaped, so to speak, and your old cassette won't run with the new chain, you might put the old chain back on and run it until both die. Consider these bonus miles, and enjoy them as long as you can. Warning this will take a toll on your chainrings, so figure what you save against what it'll cost later.

These are all excellent responses, guys, and much appreciated.

To answer your questions:

1. I believe that in the time that I have had the bike I have most likely put on 750 miles, or perhaps 1000, but I bought it 3 years used and I didn't think - well, know - to measure the chain to see how much more life I had in it.

2. I measure the chain in class, first with at 12" ruler then the mechanic used the tool. I remember something about it being over 1%...

I'll take the bike to my LBS now armed with more information and have them measure it too. The comment about if I'm going to have to replace the cassette along with the chain, I might as well ride it until both go is excellent and much appreciated!

A couple more questions: How much would this cost me - roughly - both in parts and labor? What else should I consider examining (e.g. cables) since the bike is now five years old?

Thanks again, guys. Your replies are very much appreciated!

A couple more questions: How much would this cost me - roughly - both in parts and labor? What else should I consider examining (e.g. cables) since the bike is now five years old?

Impossible to estimate, there are too many choices encompassing a broad spectrum of prices. You could do an internet search for ? speed chains and get an idea of the spread, and likewise for the cassette. Labor to change both should be fairly low, but given that you just took the course, I would have expect that you'd want to do it yourself. Both jobs are straight forward, needing inexpensive tools that are good to have anyway. If you buy a chain with a master link , say a KMC, you'll only need a basic chain tool to remove the old chain and cut the new one to size.

Between your course, and the various tutorials available online, it should be a snap.

Hmm well using a worn chain will wear out the cassette and the chainrings faster. Replacing the chain should just cost you the price of a chain. The shop should install it for free or like $5, or you can do it yourself with a $7 chain tool.

If you replace a really worn out chain you might have trouble if the cassette or the chainrings are really worn out too. Since now the non-stretched chain won't fit so well. Then you'll have to replace the cassette (or individual cogs if only one or two are problematic and you have an expensive cassette), and/or replace a chainring (if it's just one chainring that is worn out), or replace the crankset (probably cheaper than replacing all 3 chainrings).

Thanks so much for your helpful replies, guys! I now have the knowledge to know when my LBS is screwing me (and they do that in NYC), but lack the skills to do anything about it save go to another shop (my class was VERY basic).

Thanks again!