Chain ?

The other cyclist does not have any experience with it then.

Yes, with a 9 or 10 speed system you should really be changing the chain out every 1500 - 2000 miles.  By doing this you get more life out of the cassette.  As the chain wear it stretches and becomes "sloppy."  This will wear down the metal on the cassette.  Think grinding down a stump.  Eventually there will be less of the teeth on the cassette to bight the chain.  So a new chain that is tight and has no slop will be riding up on the top of the teeth and jump a few links because there is less to grip.

At that point you will need to replace your cassette AND chain rings up front.  By swapping your chain out more frequently you can go two or three chains before having to replace the cassette effectively making the gearing last longer.

<-------- Former mechanic and road racer.

Edited by Daremo 2009-09-04 3:22 PM

I've always heard that if you measure exactly 12" from one rivet to another, the chain is fine. If it's off by more than 1/16th of an inch, it needs to be replaced. More than 1/8th, and the cassette will likely have to be replaced as well. A few other things can cause skipping, though (like stiff links, or going too long without lubing it).

Depends on your bike and how well you take care of the drive train and what type of conditions you ride in. What is the quality of the chain and Casette? 2-4k seems a reasonable amount for a chain to get changed. Mine was done at 2800 on my hybrid and that gets ridden in all kinds of bad weather/rain/grit etc but I also try and clean and relube it often.

If you are not having any issues though I would not worrh about it at this point. Also the reason to change the chain and casette is that they wear together so if they have been on to long and you get a new chain it might not fit into the worn casette. You would never notice it with the old system because they wore equally. Hence the recommendation to replace the casette.

Modern drivetrains are definitely more finicky about wear than older stuff.  My new Ultegra 10-speed needed a new chain after about a year, but I've got an old Nishiki/Suntour 7-speed with probably over 10,000 miles on the original chain, and it's still not showing any stretch.  I replaced the rear gears about 2 years ago, but only because the freehub blew up, the old cogs were still fine.  Thing shifts like a pickup truck, but just doesn't wear out.

Basing it on mileage is way to variable, you could be replacing your chain way too late or way too early.  And I've found measuring a chain accurately to within 1/16th with a ruler is a PITA.

For under $10 you can get a little tool specifically designed to measures chain wear, and know exactly when it's time to replace.  Your bike shop guy almost certainly has this tool (or the cool Park Tools $25version), so I don't quite understand why he didn't just measure your chain wear (and then recommend you buy the $10 tool and measure it yourself regularly) and give you objective data rather than basing it on mileage.

As for cassette and chainrings, I think that I'd wait until I started seeing either shifting problems or noticably decreased chain life before I'd change them out.  But I tend to be cheap, and more casual about equipment than a serious racer would be...

Edited by tjh 2009-09-04 4:09 PM