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Sprocket be worn before chain? Chain skipping

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    Sprocket be worn before chain? Chain skipping

    I've replaced the chain and cassette (8 speed) about 250 or so kilometres ago.
    There's no measurable wear on the chain (tried 2 different wear checkers, and measured with a ruler), however the chain has just started skipping on the 13T sprocket under heavy load.

    I spend probably 85% of the time in this gear and sprocket, as it is my "cruising gear".

    The cassette is a Shimano CS-HG51-8 and supposed to be made from steel.

    Is it possible that the sprocket is worn enough for the chain to skip, prior to the chain wearing?
    I always thought that you should be able to go through 3-4 chain replacement prior to having to replace the cassette or sprockets.

    Anything I should check on the derailleur or anywhere else to get rid of the skipping, before I try to replace the cassette again?

    Thank you for your help.

    Disclosure: I posted this question on another ebike forum as well, however that forum seems to be broken and is displaying errors rather than posts. I'm a member and grateful reader of both that forum and the Electric Bike Forum and not one for double posting usually.

    Is it a big cha chunk or more like its trying to shift?

    Is the 13 your smallest sprocket? The smaller ones do seem to wear faster and slip easier than larger ones I suppose its a number of engaged teeth and a bit of a geometry issue. Do you often use lower gears? If not maybe a bigger chain ring to get you onto a bigger sprocket? I have had my 11 slip a couple times but I got the bike used so no idea how many miles are on it or how often it was used. I can see the wear looking at it but when I am in that gear which isn't often I'm usually not pushing that hard.


      smaller sprockets wear faster - has to do with sharper Bend chain has to make
      and fewer number of teeth chain is pulling on - larger chain ring is the way fix-

      try to get to 14 or 15 tooth cruising gear - sprockets /chain will last much longer -

      I use Tri Flow on bicycle chains - bearings - cables -


        You can buy spare cogs. I would install one with a new chain. With Sunrace casettes so cheap I just replace the whole thing.
        Universal Cycles - 30,000+ mountain & road cycling parts. Online & in Portland Oregon since 1997. West Coast & Midwest warehouses. Instant price matches. 29er, BMX, freeride, single speed, & downhill products.

        I use a Park CC2 chain checker. This gives an actual readout of chain wear as it occurs. 0-.50mm is considered new.
        This is measured with no load on the chain. IMO a BBSHD probably needs the chain changed sooner than normal. I change mine at .05mm not the 1.0mm other chain gauges use for worn. This protects the cogs and chainrings. But swapping both parts should work also.
        Last edited by Retrorockit; 07-19-2021, 10:02 AM.


          +1 you can replace just the smaller cogs

          +1 again that sunrace all-steel cog cassettes are the bee's knee's for electric

          When you look at the small cogs you notice there may be only four or six teeth of engagement, add to that the the smaller gears are where chain tension is greatest... Like another mentioned it might be a good idea to go with a bigger chain ring so you can increase the cog size for your "cruising" gear as long as you don't lose your low end. If you get stretch that is at the declared limits you may have already damaged teeth so best to replace chain before then. Chains tend to not stretch much but once they start tend to go quick so if you replace well before the limit you don't lose all that many miles and will likely more than make up for it by longer cassette life.

          I tend to purchase a new chain shortly after I replace and just hang it on a nail in my workshop. Every know and then I'll pull the chain off the bike and hang it on the nail next to the next new chain and it's silly easy to see the exact overall stretch. I replace well before there's half a link of stretch - last one got 3000mi with about 1.5mm total stretch and the cassette was fine.

          Another thing is to always try and turn the pedals as fast as you feel cozy with since this reduces the chain tension and everything will last longer


            That is a good point about what speed the chain ring is going. I had a friend riding one of mine recently and he was always in a higher gear than I was so he had to be pulling a lot harder on the chain than I was. Remember a typical person is only putting out maybe 250w so if you have a 750w mid drive and are often pulling the max thats 3x what they figured would be going through most drive trains. If you do a lot of throttle its hard to tell how hard its pulling if you don't look at the gauge or try some pedaling from time to time to see what rpm its at. I try not to sustain much over 500w. Sure I get bursts or some nasty hill climbs that go over 500 but most of the time I can keep it in that range by shifting or speeding up a bit.


              Thanks for all your suggestions guys, I really appreciate it.
              I understand that there is more wear on the smaller cogs, however I've already got a 48T chainring at the front. Maybe my cadence isn't as good as it could be.

              Anyway, what gets me is that both the chain and the cassette are quite new (as I said ~200kms on them since installation), there was no skipping until now and there is no measurable wear on the chain.

              Maybe I need to turn my attention to the way that the derailleur is set up?


                Originally posted by Letterman View Post
                ...Maybe I need to turn my attention to the way that the derailleur is set up?
                If it shifts well that's unlikely to be an issue with wear

                I understand without a sensor it's very difficult to judge but any idea what your typical pedal cadence is? It's easily calculable based on speed, cog teeth and wheel sizes though - I've got a preadsheet calculator for that if you like but it's pretty easy to do on paper. If you are turning once per second (60rpm) you are in a happy zone - I consider the very lower bound of good pedaling speed to be ~50rpm. I got a cadence sensor quite a while ago and it's near the top of my favorite instruments.

                I'm old and have one leg and when I first started riding 50-60rpm was all I could muster for continuous riding - I couldn't keep my plastic leg on the pedal above 70rpm... but 50-60rpm is not a bad place to be in my opinion for both the motor and driveline. Faster is better and these days after a lot of miles riding and a new improved leg I now typically turn in the 70's rpm continuously and think this is a really good place.

                Hammering the throttle is also hard on the driveline. My initial motor PAS tunes were really hard on drivelines too - I could see how much current was getting slammed by the controller on batt-man logs. I had gone through my share of 11t cogs and one or two 13t when I was running aluminum - that's how I know they are easy and cheap to replace

                Regardless, fixing the motor PAS tunes, going all-steel cogs and upping my pedal cadence have fixed that issue for me...


                  If you don't hear it making the clicking sounds like its trying to shift I would not suspect the derailleur. You can try adjusting it and see. Most shifters have an adjustment barrel right on the shifter so you can just give it like a 1/4-1/2 turn while you are riding and see if it makes a difference. If you can adjust the cable so its perfect in one gear but then is making the clicking in other gears that could be a sign of something being bent or a miss match in parts.

                  If your display has a watt meter you can get an idea how much stress you are putting on things. Try the same pace pedaling and throttle to see how much your pedaling is adding. You can then try a lower gear so you and the motor are spinning faster. Some conditions a gear or two will drop the power required 1/3 to 1/2 which is a lot less stress on everything.


                    Thanks Azguy and 73Eldo. I don't have a throttle, the 13T cog is made from steel and shifting seems quick, clean and silent in all gears. I'll have a look at cadence over the weekend and hope not to be embarrassed by not being able to keep up with a guy with one leg (no offence Azguy, I admire you :-) ).

                    Ok, so I've done another little experiment, which may be completely useless but hear me out.

                    With the chain in the largest cog, I manually rotated the derailleur body "down", to push the upper pulley away from the cog. Then I let go and took note of how many teeth the chain was fully engaged with at the bottom of the cog.
                    Then I did the opposite and rotated the derailleur body "up" to push the upper pully closer to the cog, and let go.
                    I noticed that there was a difference in the "end position" of the upper pulley after pushing down and then up. After rotating the derailleur body back up and letting go, the chain was sitting noticeably closer to the bottom of the cog and had engaged with at least one additional tooth .

                    Could this point to an issue with the tension of the springs in the derailleur? If so, any idea how to check or fix it? I've done about 2500km in total with this derailleur, which is a simple Shimano Altus 8 speed (M310 I believe).

                    Thanks for your help and patience.


                    • AZguy
                      AZguy commented
                      Editing a comment
                      I don't think that "hysteresis" you are seeing is a big deal unless it's a lot. Derailleurs have a specification for how far the guide pully should be from the largest cog (it's a range) and there's an adjustment for it. If it can be adjusted so it stays int he range when pedaling and shifting (not pushing it around so much) the I'd call it good.

                      OTOH it might be due for a cleaning =]

                    How does your chainline look in the 13t cog?
                    Are there any tight links in the chain?
                    If using a quick link is it the right one for the 8 speed chain?
                    Is the cassette tight?
                    Is the main cluster all nice and parallel? No burrs, chips or other debris stuck between cogs?
                    Are you shifting to the 13t from a smaller cog under high load?

                    I can't think of a good reason for your problem.


                      The quicklinks can get bent from rough shifting, or cross chaining. They're pretty good in tension, but bending can cause an issue with them.
                      I have had one tight link do this. This can show up as the derailer kicks forward when the tight link goes through the jockey wheels when pedaling with no load.
                      Last edited by Retrorockit; 07-28-2021, 11:50 AM.