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I just installed a new chain on my 2002 Trek 2200 Road Bike. The old chain was a Shimano 9 speed that I installed 18 months and about 5000 miles ago. It had stretched modestly and was full of winter cruft/grime. The new chain is a SRAM 9 speed, my first time using the gold snap ring system. I followed instructions and made sure I have the same link count as the chain that came off the bike. The cassette was new with the old chain, so it has about 5000 miles on it and doesn't appear to have significant wear. After installation and a clean/wipe/lube/wipe, I took it for a 15 mile easy ride at about 15-16 mph. It shifts perfectly and I didn't have to make any adjustments to either derailleur. Three times, however, when putting it under stain (once on a modest hill climb, once starting from a stop sign in a fairly big gear, and once on an acceleration coming out of a sharp turn) it skipped several teeth and caused my foot to slam down hard. On the hill, it actually hurt as I had my weight off the saddle (not really standing) and I came down hard on the inside of my thigh. I think all three were on the right side (power train side) pedal stroke, and I don't think they were all in the same gear. I'm pretty sure it was the rear cassette that skipped, not the front chainring, but it did happen really fast each time. I will also say that it's not like these were the only three times I put substantial pressure on the pedals in the ride - I wasn't going hard, but I wasn't being tentative or anything. Also, in case it's relevant, it was cold, about 40 degrees F or about 4 degrees Centigrade.

My question: Is this going to get me hurt, or will the new chain 'settle in' over a few rides? I searched here and pretty much got confirmation of what I had previously thought, that you always get a new chain when you get a new cassette, but you should be able to get a few chains out of each cassette. Thanks!

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When was the last time you replaced the cassette. Perhaps it is too worn. Mixing old cassettes with new chains can sometimes cause problems. –  Kibbee Feb 26 '13 at 20:12
    
I replaced both cassette and chain in the Summer of '11, about 5000 miles ago. I thought I would get more miles from the cassette, and think I have done in the past. –  Dan Catlin Feb 26 '13 at 21:19
    
5000 miles is about what you can expect from a cassette -- maybe more, maybe less. (And 2000 miles is about what you should expect from a chain.) –  Daniel R Hicks Feb 26 '13 at 23:32
    
I've heard people changing their chains at 2000 miles, but I use one of those chain measuring tools and it was within tolerance even at 5000 miles. I guess I thought 2000 was a bit like changing the oil on your car at 3000 - used to be the standard but most new car manuals say 5000 or even 7500 miles is fine with new tolerances, etc. Maybe the new rule for me is change them together once a season or every 5000 miles or so. Thanks. –  Dan Catlin Feb 27 '13 at 13:35
    
5000 miles out of a casette is what you can expect? Wow, that's like ... an oil change interval on a car. And I'm assuming that's a good quality casette, not something from a "bicycle shaped object?" Geez what an industry, this cycling. –  Kaz Mar 2 '13 at 1:28

2 Answers 2

You might need to get your derailleur adjusted; the new chain would be shorter than the previous chain and one might have bumped the derailleur upon installation.

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Hmm. I would have thought the new chain would be a tad shorter, but the shifting is flawless. The only problem is those skips on the maiden voyage. Unfortunately, it's raining bad today, so I can't give it another try... I'll bring it into my favorite shop over the weekend if I don't get it sorted. Thanks. –  Dan Catlin Feb 26 '13 at 21:22
    
A new chain is not necessarily longer. New chains typically come with extra links that you can take off to meet your needs, but if both chains have the same number of links, the old chain is longer as it has been stretched. –  hillsons Feb 26 '13 at 23:14
    
ugh, I meant shorter. Should have proof read... adjusting. –  Mimi Flynn Mar 1 '13 at 16:59
    
If you've sized the chain correctly, the derailleur adjustment shouldn't have to change. –  Batman Aug 2 at 19:19

Over time an old chain and cassette wear together, so you don't notice the wear until it gets really bad. When you replace the chain while leaving the old cassette the tooth profile is no longer correct and the new chain will skip off of the teeth, especially under load.

Unfortunately it won't get better and the only recourse is to replace the cassette as well. In the future you can save money by changing the relatively inexpensive chain more often as the cassette wears faster with an elongated chain.

More info: http://sheldonbrown.com/chains.html

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Thanks for the Sheldon Brown article - I hadn't thought to check his site. If it adds anything to the conversation, I hadn't really noticed any wear - just thought it was time - the chain measurement tool was still (barely) in spec, and there is no obvious wear on the cassette, nothing like in the pics on Sheldon's site. –  Dan Catlin Feb 26 '13 at 21:20
    
I seldom allow a chain to run more than 2000 or so miles, especially on bikes that are run in foul weather and almost never have to chain cassettes. –  Rex Kerr Feb 26 '13 at 22:18

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