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I figure the jockey wheels on my derailer will last nearly forever, but what about the rest: cassette, chainrings, and chain? How many miles, kilometers, or furlongs do they normally last?

I know that there are definite signs of worn out sprockets—what sort of mileage is typical before the point where the wear is significant enough to require replacement?

This is for a commuter/touring bike with Shimano 105 components that is reasonably well maintained. I clean & lubricate the chain every few weeks.

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What type of bike? And what kind of riding? My commuting bike and road bike components have vastly different lifespans. –  user313 Sep 17 '10 at 17:00
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Also, what kind of maintenance do you give those components on what kind of schedule? –  freiheit Sep 17 '10 at 17:11
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As commented above, it's impossible to answer this without knowing how hard you ride the bike and how well it's maintained. Whether you replace your chain regularly is of particular interest. –  Neil Fein Sep 17 '10 at 17:16
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I was trying to keep this general, so as to be useful to others; I didn't realize that so much would depend upon the style of components. –  Drew Stephens Sep 17 '10 at 17:39
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4 Answers 4

up vote 8 down vote accepted

Mileage will vary greatly depending on the riding conditions and component maintenance. Personally, I've never tracked the mileage of my drivetrain components. But I do know that I replace chains far more often on my commuter bike than on my road bike.

Ok, I pulled out my copy of Zinn and the Art of Road Bike Maintenance...

Chain life: 1,000 - 1,500 miles in dirty conditions or infrequent lubrication. Lighter cyclists riding on clean, dry roads might expect 2,000 - 3,000 miles with poor maintenance and up to 5,000 miles with a daily high-quality lubrication.

Zinn also says that he gets almost infinite life out of his chainrings and cogs! He said that in the section on checking for chain elongation.

Here in Portland, commuting year round, I'm probably near the bottom end for my commuter bike.

wdy

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I'll add that I change my chain at least once a year. –  curtismchale Sep 17 '10 at 19:30
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The key to the 'infinite life' for chainrings and cogs is frequently checking for chain stretch, and replacing the chain at the first sign. Running with a stretched chain deforms the ring teeth and makes it so all the components have to be replaced at the same time. –  Gary.Ray Sep 20 '10 at 3:27
    
@Gary.Ray - In Zinn's book, the only index entry for chainring and cog lifespan is to the page/section on chain elongation. So, chain elongation is definitely the key to chainring/cog life. –  user313 Sep 22 '10 at 20:24
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Drivetrain components tend to wear in this order:

  1. Chain
  2. Rear cassette/sprockets
  3. Front chainrings

(and the teeth on your derailleur's jockey wheels may last, but the bearings may not)

The chain is usually the culprit for wearing out the other two. As it wears, the distance between links effectively increases, and the mismatch between the links and teeth will grind away at your gears. So the key to making your cassette and chainrings last is to change the chain before it wears too much. I use a Park Tool chain measuring device -- it slots in between the pins on the chain so it's a bit more accurate than a ruler.

Keeping the chain clean will help increase its life. Also keep in mind that 9- and 10-speed chains (and perhaps 8 as well?) are narrower than the other chains. Their construction allows more gears to fit in the same space, but it also means that they wear much faster.

I've stayed with 9-speed and my chain lasts at least 1500km with a lot of riding in wet weather. Every time I've pushed it (and ignored my chain tool's advice), I've had to spring for a new cassette afterwards. I remember chains on my older bikes (7-speed) lasting much longer than this.

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Do 9 & 10 speed chains really wear faster? I can see how they might be designed for weight and performance over longevity, but do you think it is just the narrowness? –  shabbychef Sep 18 '10 at 20:58
    
@shabbychef: It matches my experience with 7 versus 9 speed and is also something that my LBS pointed out. It could be due to the narrower chain, less material, or perhaps the narrower cogs focus the stress over a smaller area. –  darkcanuck Sep 19 '10 at 1:02
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I've heard different rules of thumb (rule of thumbs?) about how much use you can get, and remember none of them. What I do know is that not lubeing a chain often enough--actually, cleaning and lubeing--will cause it to wear such that it 'stretches'. Not stretch like taffy, but gain overall length due to the pins and bushings in the links wearing down, getting slightly more room in how they link together. Once the chain stretches it wears the teeth of the cassette and chainrings much rapidly. Bottom line: lube and clean your chain often enough and everything else will last longer.

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and you can measure a chain with a regulat 12" ruler. Pins should line up at 0" and 12" –  curtismchale Sep 17 '10 at 22:16
    
Rules of thumb = more than one rule of the thumb type. Rule of thumbs = one rule about more than one thumb. The first one is correct here. (The second one isn't likely to be correct anywhere.) –  Wayne Johnston Sep 26 '10 at 19:38
    
I heard a rule of thumb--no, wait, there were 2 of them. –  Jay Sep 27 '10 at 6:49
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As darkcanuck mentions, make sure you check the chain for wear and when it gets outside of acceptable limits change it. If you don't then you'll end up having to change other components too.

I left mine too long (much, much too long) and ended up having to buy a new cassette and chainrings. The rest of the drivetrain may survive for years but only if you look after the chain properly and and replace it when necessary.

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