anthonybkny

So after buying one of those chain checker tools, it showed .5 stretch. I figured I would replace the chain even though it isn't that stretched yet. Installed new chain, now the smallest cog slips even under very light load. I've readjusted my rear derailier and it seems to shift great. The teeth on the rear cassette look fine but what do I know. I don't use the smallest cog very often and the bike only has about 1700 miles on it. Where should I go from here?

Blue Belly

That's typical of a worn cassette.

anthonybkny

Ok. I'm not a bike mechanic but since the chain isn't stretched much and it only skips in the smallest cog, which I don't really use, could it be anything else? Am I missing something? I reinstalled the old chain and no skip and shifts flawlessly. The reason for the new chain was that I wanted to head
off wearing out my cassette. If it is indeed my cassette, should I just run the old chain until I start having issues?

Blue Belly

You'll likely wear the chain rings also. It doesn't do it with the old chain because the cassette ha worn to match it. When you put the new chain on & step on the crank, it's trying to pull on one tooth at a time. When it starts over the top I skips in certain links.
the smallest ring wears the most because it has the least teeth & it skips easier because it's teeth are at a more extreme angle/tighter circumeference.

anthonybkny

Gotcha. Thanks for the help guys. So new chain and cassette. If I have issues up front after, new chain rings also.

FBinNY 

Not so fast.

The way you describe things, it doesn't sound your problem is related to sprocket wear. Take the time to do a full and proper diagnostic before you throw away dough replacing parts which aren't the problem.

If the skipping is only happening on a sprocket you don't use much, while the ones you use more often, then sprocket wear doesn't make sense at all. The new chain should mate best with the least worn - newest - sprocket. So faced with the logical conflict you need to open up the options.

So to start with, there are different types of chain skip.

1- Wear skip, which shows up as skipping under load, with the amount of skipping sort of proportional to the chain tension.
2- Shift/trim skip where the chain can skip randomly because the RD isn't trimmed right, and it's trying to shift between tow sprockets.
3- Stiff link stiff, where the chain is skipping because a single link doesn't spool properly onto the sprocket. Since it's a chain issue it would happen every 2-3 turns of the crank (# of chain links / # of chainring teeth). Stiff link skip most often happens on smaller rear sprockets, but is rarely confined to a single one.

So we've ruled out No.1 (tentatively), and No.3 doesn't fit the description, that leaves No.2 . The fact that it shifts well and runs smoothly seems to argue against a trim issue, BUT it runs well on all except the smallest sprocket and that may be the key clue. The trim on all sprockets is set by the cable adjuster, except for the smallest one where the trim is determined by the limit screw. I suspect that the limit is slightly tight (trimmed inboard) which is why it skips. Adjust the limit outward, or fine tune it while watching the chain run in high, and your problems should go away.

One more thing. Limit screws don't magically tighten, so odds are your hanger is very slightly bent inward. Not enough to worry about yet, but if the hanger moved in and took the outer limit inward, it did the same with the inner (low) limit, so take a moment to check and adjust that also, before you overshift the chain into the wheel.

anthonybkny

Thanks fb for your post. Your thinking skills are excellent. And makes complete sense. However I gave it another test ride and it skips in a few other gears as well, had to give it more torque.

FBinNY 

OK so it might be a worn cassette after all, but at only 1700 miles, and where the chain was on the chain checker, it's pretty early for this kind of wear.

So you have a few choices. Often marginal skipping resolves as the new chain breaks in to the sprockets, so you can ride it a hundred miles or so if the skipping isn't bad, and see if things improve. Or you can replace the cassette with a new on, but save it for use when this chain has more wear.

As far as the chainrings go, it's just about impossible for them to be worn enough to need replacing.

Kotts

What is the history on the bike? How was it ridden before you got it? How many times has the chain been replaced with that cassette? How many miles on the chain the OP replaced (or how much wear) might be irrelevant to whether the cassette is written out, if it was accused previously.

anthonybkny

Bike was purchased new this summer. Has 1700 miles on it. All original drive train
heres a pic of the cassette, do this look worn to you guys?

anthonybkny

Another pic

anthonybkny

And last one, sorry for the separate post, working from an iPhone and I can't figure out how to add more than 1 attachment per post

vredstein

Is there any possibility you can get your hands on a new small cog to just pop on there and see if the problem disappears, then install the old cog and see if the problem reappears?
If you got the bike from a lbs, maybe theyd be willing to install just a new small cog for test purposes.

speedy25

Still learning about the newer hardware. Is it possible the OP's problem is from the wrong chain or the wrong brand? With so many choices its easy to buy the worng part. I know of wrong chains causing shifting problems, could it cause skipping problems too?

-SP

Maxturbo

That cassette is SHOT (teeth), plain and simple for whatever the reason.

Phil_gretz

Holy Cow! 1700 miles and the wear on the smallest three cogs is visible. I've not seen that before. Does the OP use high gears and really torque the cranks? And ride in very gritty conditions?

anthonybkny

im about 240lbs with very strong legs and at times, definitely lay the torque down. ill chalk this up as a rookie mistake and be more gentile on the new drive train.

AnkleWork

I don't see what the other posters think they see. Your cassette appears to be no more than slightly worn. Compare it to a new one. Perhaps others mistake the profiles on the *back* edges of the teeth for wear on the driven edges.

Maxturbo

Look at how bent and out of proportion the small cog tooth at the center of this pic is...

Compare the tooth ramps. One is perpendicular, the other at a 45.

FBinNY 

The bike is there to serve you, not the other way around. There's no way you can be more gentle, because you need tomproduce the torque to move the bike. You're weight, combined with any kind of hilly terrain, will mean that you'll never see the chain or cassette life of a lighter rider in the plains.

About the only thing you can do is to use the larger chainring, and larget sprockets vs. the small ring and smaller sprockets. This lessens the torque at the drive train for the same input and output.

That and some better chain lube.

BTW- I see only marginal hooking on one sprocket, so I'd save this cassette and switch back to it as soon as the new chain begins to stretch. Then you can use the new cassette with a new chain.

Maxturbo

What would you deem severe then?

FBinNY 

More than 1/16" of wear on the working faces.

I have freewheels and chainrings where the teeth are worn to almost their original width. The chianring on my commuter is well past even that mark, and I'm now riding it to see how little tooth is necessary for function.

AnkleWork

Yes, I did compare it -- to a new one . . . they're made that way. The edge of the tooth you mention barely touches the chain.

Maxturbo

OK, but why are the larger (non-chain slipping) cogs more uniform in shape / appearance by design?

It just seems odd to me.

davidad

How do you maintain the chain? Chain life is almost always an indication of maintenance. I have an 8sp chain with over 11k miles on it and it shows about 1/32" of wear(stretch). The cogs are still in good shape.
You might check the der. hanger to see if it is bent. That will effect shifting as much as chain wear.