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Chain skipping under pressure
#1
Hi,
My (double) road bike with Shimano 2300 has developed a problem. If I put pressure down on the pedals, especially uphill when I'm out of the saddle, my chain skips. I've recently had a brand new rear derailleur put on the bike, with new cables, all adjusted by a bike shop. I've checked the bike on a stand and the gears look in perfect alignment, they shift brilliantly in the stand. The chainset is well greased too...

I've thought these are the most likely, can anyone advise as to what is most likely? Or if there's anything else you'd expect?

-My shifter, which is a 2300 STI (not top-of-the-range), is about 5 years old, done a fair few thousand miles, is there any possibility that this could be struggling to shift the gears on the rear cassette?

-My chain, which isn't the original from the bike, might be stretched? Is there an easy way of checking this at home? I thought it might not be working particularly well with the new derailleur?

-My front small chainring is the original in the bike, which didn't fare well one winter and since then it's worn badly, to the point where the teeth look like claws pointing in the direction of rotation. Could they be catching the chain and causing the skipping? I thought this because I haven't had any skipping when pedalling in the big chainring, but I suppose there's not as much torque as I'm rarely out of my saddle in the big chainring.

Thanks very much in advance,
Joni
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#2
Most likely, you need a new chain and rear cassette. Changing your small, front chainring might also be good, but less likely to be the main factor.

If you google "measure chain stretch", it is very simple. But note that by the time the bike starts skipping like this, you generally need to change the chain AND the cassette. Unless you change the chain very frequently, chain and cassette usually have to be changed at the same time.
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#3
Dave is correct - as it only skips under pressure derailleur adjustment would not be an issue, and your description is a classic symptom of chain wear. I would hope the new derailleur was not put on to address the skipping - any shop should recognize the problem as drive train wear.

The chain and cogs wear together, and generally replacing the chain only, once past a certain point, will result in continued skipping, usually in the smallest cogs. The chain will wear much slower if you use higher rpm's.
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#4
Given your description of the issue, like the others, I highly doubt that the RD and cables had anything to do with it.

I would also replace the chain and cassette (or freewheel); in addition I would replace the crank set (because you can get a new crank set for about the same price you can get new chain rings) or the inner ring. You may be able to find a good deal on an inner ring only; and take this opportunity to decide if you want a different number of teeth in you inner ring to better suit your riding style and routes.

For example, when I changed the crank set on my WT, I went from 52/40 to 50/34. Sometime in the future; I'll probably be swapping the 34 for a 38, 39 or 40. The jump between 50 and 34 is bit extreme, and I don't need 34 for where I ride my WT.
Nigel
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