SamSam77

Essentially, my question boils down to whether or not my front chain ring is worn down and needs replacement. When I research these things online I can only find extreme, obvious examples of when to replace parts. Less obvious cases, at least to my untrained eyes, are harder to find. (Apparently I am not allowed to post photos here for others to judge.) The chain ring is certainly worn, but is it worn enough to explain my chain slipping problems?

For added context...

My bike is just shy of 2-years old with, as a very rough estimate, about 2000 miles ridden.

I let my chain wear way past the point when it is generally recommended to be replaced. As I understand, now, the rule of thumb is to replace the chain when it has 'stretched' about 1/16" past the 12" mark on a ruler (lining up the 0" mark with the center of a rivet, the rivet on a taught, new chain should be at the 12" mark). Once the chain gets to about 1/8", it wears the cassette to match the chain. Embarrassingly, I let my chain get to 3/16", so it most definitely needed to be replaced. To my eye, the cassette didn't look so bad, but my eyes are not well calibrated to spot such things so I decided to replace the cassette too.

As long as I was replacing the cassette, I decided to adjust the gear ratios to ones more to my liking, instead of what came stock with the bike. Originally, I had a 9-speed, 11-34T cassette but really only make use of the top half of the gears. So I replaced it with a 11-25T cassette, effectively loosing the gears I never used and giving me a finer transition between the gears that I do use, Since the news gears were a subset of the old gears, I kept the chain length (number of links) the same from before. So the things that changed are: new chain (same length) and new cassette (different gear ratios).

Now, after making the replacement, my chain is slipping like crazy when I pedal with very much force. It does not really slip when I'm watching it, so I cannot be 100% sure of what's happening but I think it is slipping on the front chain ring. Aside from the fact that the chain and cassette are both brand new, evidence that points to the chain ring includes the fact that on one of the big slips, the chain fell off the ring. Additionally, when I change to the biggest ring from the middle ring, the slipping does not seem to occur. (Out of my three front chain rings, I'd say I use the biggest ring ~10%, middle ring, ~90%, and the smallest ring ~0% of the time).

Freerojo

I am not sure you should have put the new chain on based on the length of the old one since you changed to a different sized cassette.

woodcraft

Chainring is not going to wear out in 2k miles, especially if used 10% of the time.

Actually unlikely that the chain would wear out in 2k miles either.

The chain should be shortened since the cassette is much smaller, & check the RD adjustments.

SamSam77

Yes, I agree, from what I've read, chainrings should take much longer to wear out than a mere 2000 miles. That being said, the chain itself was definitely worn out...rulers don't lie, not to mention how much I can expand/compress it along its length after removing it and laying it flat on a table. The cassette was probably a more borderline case, I am less sure about that.
To clarify, previously, I hypothesized that only the middle chainring was wearing out, which is the one I use 90% of the time. The other two rings (smallest and largest) should not be worn much, and it's only when using the middle chainring that I experience this problem.

Changing the derailleur cable tensions changed how easily it would shift gears but didn't seem to affect the chain skipping problem.

The chain length was the most likely alternative explanation that I was considering, instead of chainring wear.
The reason why I discounted that idea was because the gears in the new cassette should be within the same (smaller) size range as the old cassette. The smallest gear on the new cassette equals the smallest gear on the old cassette, and the biggest gear on the new cassette is smaller than the largest on the old one (roughly equivalent to 3 out of 9). So if the old chain worked on the old cassette, it should still work on the new one. I understand that I have unnecessary slack built into the chain now, since I'll never go to those largest gears that are now gone, but not having them at all should be the same as having them and never using them as far as the chain is concerned, no? My understanding must still be lacking somehow. The problem would be more obvious to me if I had an even smaller smallest gear on the new cassette (or larger largest gear, for the reverse problem), but that is not the case.

If I do just need to shorten the chain further, I much prefer that problem to solve than replacing the chainring.

79pmooney

I run a variety of cassettes with the same chain and derailleur all the time and don't change anything except make sure the limit screws and cable tension are right. Yes, you can optimize the chain length for the cassette you are running and get slightly snappier shifting but it is far from necessary. On my 9-speed I run form 23 to 28 for the large cog. On my 7-speed, I run from 21 to 28. (I was riding the 7-speed this afternoon. Was thinking that I had no "legs" as 42-28 was way too hard! This post reminded me I was riding my other wheel with the 12-21 FW.)

Ben

dsbrantjr

I suspect that your middle ring is worn, as it is the most heavily-used one and this is the cause of skipping while using that ring, as demonstrated by the lack of skipping on the big ring. The chain should not NEED to be shortened for the smaller cassette, as 79pmooney points out, it will just work the same as if you had shifted to smaller cogs on the larger cassette. A chain worn to a measurement of 12 3/16 is pretty worn regardless of the mileage and could easily have worn the ring to where it would not work with a new chain. Check the engagement of the new chain with the middle ring as shown in this article: https://www.sheldonbrown.com/chain-wear.html

woodcraft

I misread your post & thought you were saying the skipping happened big ring but not middle one.

SamSam77

When I put the bike up on a stand, so I can carefully watch the chain on the front chainrings, I do not see anything obviously wrong with how it is engaging on the teeth under load. The middle (problem) ring looks to be just about the same as the largest (problem-free) ring, at least under modest forces.

Nevertheless, it would seem like the middle ring is worn and I guess I'll have to replace it as I feared.

lobstermike

Have a look at the shape of the teeth on the middle ring, compared to a new ring...there could be a big difference.
A way to increase longevity of the middle ring is to use the granny ring for the biggest sized gear cogs, the middle ring for the middle gear cogs, and the biggest ring for the smallest gear cogs.
This stops putting the chain under unnecessary sideways stress, thus making your components last longer.

Bill Kapaun

Does it slip while on any specific rear cog more than the "other" rear cogs?

You might study "B" screw adjustment. It "might"? help?? You should be able to back it out some since you've gone to the smaller largest cog.

SamSam77

There is no obvious difference that stands out to me.



No, I think it slips equally on all rear cogs, near as I can tell.

I did not know of the "B" screw before. After researching it, I tried to make the adjustment but the screw does not seem to change anything: pulled all the way out looks the same as screwed nearly all the way in.

3alarmer 

...if your chain was that much elongated, it doesn't take all that long to wear the teeth on an aluminum alloy chainring. Given your description of not slipping (I presume by this you mean skipping or jerking when under load from your pedaling) in the biggest ring and acting up in the middle ring, that's what I would change out first to attempt a remedy.

I guess it's remotely possible your new cassette might be loose on the freehub. Another possibility is a tight link in your new chain if it was installed with a chain tool and not a quick link. But if those areproperly installed, go with the chainring. You can't really apply enough pressure on the stand to replicate this problem. At least, I can't. I run into it with old freewheels from time to time, and it never shows up until the first ride with a new used freewheel.

gregf83 

If you’re new chain and cassette are slipping it’s almost certainly due to a worn chainring. Replace the chainring and the skipping should stop.

TakingMyTime

Could this just be the pawls on the freehub not engaging 100% of the time and giving the effect that the chain is skipping? Sorry, but I'm having a hard time figuring out exactly what you're trying to describe so I thought I'd just throw that out.

Loose Chain

I installed an entirely new drive train, new cogs, new freewheel, new crankset and new chain, all matched 105 stuff and I had a skip. It would skip on any rear cog chosen and did not matter which chainwheel I was on. Sometimes it would not skip, other times it was continuous. After much frustration I inspected the new chain and found that a link was tight and wanted to bind. Not one adjacent to the rivet I installed, not even close. I used my chain tool to loosen the link and no more skips.

SamSam77

The new chainring that I ordered finally arrived and I installed it this evening. Aside from cosmetic differences, the most notable wear that I saw was on the leading/pushing edge of the teeth, the metal was 'mashed in' and blunted a bit, like it was chain was pressing back against the teeth with so much force the metal deformed. Running my fingers along the face of the chainring, the tailing edge of the teeth was relatively smooth while the leading edge had a rough lip since the metal had deformed slightly in that region. Of course, the new ring is smooth on both edges of the teeth.

Upon taking my bike for a test ride, after the replacement, the chain skipping seems to have stopped when using the (new) middle ring. So the problem is solved and the chainring, the most obvious culprit, was responsible.

mtandrbker

i have a similar issue with both new chain and new cassette. mine only skips under load and constantly in 8th gear but no other gears. i was thinking my issue is the old chain set also since i have ruled out everything else . my chain is the same size as my old chain