fmt_biker

You've seen this type of thread a million times,l and I apologize, but would like to know what visually to look for.

Surly LHT, 4800 miles on drive train. I noticed chain nose that would go away after through chain cleaning/lube. I replaced the chain with a SRAM 9 speed and cleaned all remaining drive train parts. I went for a test ride, and found it was fine in most gears, but skipped on (any chain ring) X (11,13,15) cogs with any thing more than a little torque. It wasn't skipping before I changed the chain, just noisy. This bike spends 80% of its miles in cogs (11,13,15). Bikeforums search seems to indicate that a new chain can start skiping on worn cogs. Some threads indicate that the cassette should last 2X chains, some disagree. I'm fine with this advice and order a new (next model up) cassette which should arrive by Friday. As not to damage the chain, I'm riding another bike in the meantime.

I find plenty of pictures on the web that shows the typical wear on cogs, but I just don't see the wear, but then again, I've never really done this kind of stuff before. Here's a cell phone pic of the cogs (smallest three skip). Do they look worn to the experts here?

FBinNY 

Even experts have trouble predicting whether a new chain will skip on the old cassettes, especially on the most used or smallest sprockets. The acid test has always been to try and see. With a trained eye, one might get a hint, but as I said, it's very hard to know.

The reason new chains skip is that the pitch is shorter than the worn chain and they're tighter, and less accommodating of the deformed sprockets. Over time the backs of the teeth (where the load is carried) wear. As the chain wears, this process speeds up, and eventually there are pockets which allow the chain o settle a bit deeper. However, there's little or no wear at the tops of the teeth, and eventually it reaches a point where the sweeping link arcing into the sprocket bumps against the back of the next tooth. Since there's virtually no tension in the lower loop, that bump is enough for the chain to climp up to the tip, and slid forward when it rotates around to the top.

If you take the chain off the bike, you can test by looping the chain over the sprocket and pulling it forward. Then try to unfurl the chain from the slack end. If it snags or if you feel the bumping I'm describing, then expect chain skip.

BTW- if th skipping is minor, or occasional, and you can live with it, it'll self resolve as the new chain wears those back/top corners and can engage smoothly again. Or you can use a grinder to relieve the top/back corners, but it's a slow PIA process, only worth it if the cassette is expensive.

fmt_biker

That was a very good explanation, thanks. I cannot see myself grinding the sprockets ... when a new cassette is all of $44 Hopefully I'll be good to go with the new cassette!

ThermionicScott 

If you mostly use the smallest cogs (which are prone to wearing out faster than the rest), switching to a tighter cassette would help you spread out the wear, too. I'm guessing you currently have an 11-34. An 11-28 would give you a 12T and 14T without taking away a great deal of your low gears.

fmt_biker

I probably should have done that, but I had already ordered another 11-34. I bought the bike with idea of touring and the low gears would be useful for that. Reality is, however, that I don't have time to tour. But I love the stable and smooth ride, so it gets about 75% of my miles.

I guess I still hold out hope that I'll tour on it some day, and if so, I'll be thankful for the 34!

Bandera

Having a couple or three cassettes for a machine makes a lot of sense from an efficiency standpoint as well as spreading the wear.
If you are not using the 11-34's bottom or top cog(s) get a 12-28, 12-25 or whatever gets you up the stiffest local climb w/o drama and park the wide range for touring.
Tighter ranges make for smaller steps & greater efficiency. Having cogs that are not used normally is like stepping back to a 7 or 8 speed cassette when you paid for 10.

In the Shimano world 5xxx or 4xxx spec are less $ than 6xxxx and are interchangeable, just takes 10 minutes w/ a chain whip & lockring tool.

Get a chain wear tool for $5, replace chain as necessary and all cassettes will hum happily along.

-Bandera

fmt_biker

OK good point. Just ordered an 11-28, now I have a variety

Bandera

Here's my bias as an old school club rider & racer from when a 53X13 (107 GI) was the top gear at Nationals:

Are you doing down-mountain time trials? How much do you ride in a 50X11 (120 GI) >100RPM?
Ditch the 11 for a 12 and tighten up the range, it's much more useful, Really.

-Bandera

fmt_biker

Well the LHT has a 48 tooth large chain ring, so believe it or not, I do spend a fair amount of time in 48X11. But there certainly have been times were I wished the jump was more fine between in the 11-15 range. Plus the cassette will be lighter. Oh wait, it's a boat anchor LHT, but I guess every little bit helps.

fmt_biker

I just want to add a postscript to this thread. I installed the 11-28 and re-adjusted the rear derailleur, and all's good now no skipping.. I was a little surprised how much adjustment the RD needed considering that it was supposedly the same spacing, but it's an easy job, so who cares.

Thanks again.