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    BBSHD skipping on highest gear...

    Last year I converted a Townie 8D Balloon with a Luna BBSHD mid drive kit (says capable of 1600 watts peak output). I paired it with a high capacity 52V battery. At the time of the conversion I installed a new KMC 8x chain, the man I spoke with at Luna agreed that would be a good match. The bike handles great and has been a thrill and a joy to ride and own with one main exception. The chain keeps skipping on the smallest cog when I apply full power.

    I have since tried shortening the chain, upgraded my chainring from the stock 46 to 48 teeth, replaced my cassette and chain at the same time, and replaced my rear derailleur and cable. I still have the same issue at full power the chain skips on the smallest cog. The replacement cassette is an SRAM PG-850 11-32 8 speed and I have kept with the KMC x8 chain.

    The bike is fast and I thought I could be happy just avoiding the top gear, but it really is used quite often so if I could get this sorted, it would make my bike so much more ridable. Any suggestions on what I should be looking at would be greatly appreciated.

    #2
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      #3
      It sounds like you just may be exceeding the capabilities of an 11 tooth cog. Remember this stuff is designed for human power which is more like 250w continuous with bursts of maybe 350w. The reason the 11t is really a problem is there just are not that many teeth to share the load. Lekkie makes a 52t chainring. Or get a BCD adapter that lets you use standard chainrings if you don't need the deep offset of Eclipse or Lekkie rings. That should let you stay off the smaller cogs. Question will be will you still have low enough gears for hills or wind?

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        #4
        Originally posted by 73Eldo View Post
        It sounds like you just may be exceeding the capabilities of an 11 tooth cog. Remember this stuff is designed for human power which is more like 250w continuous with bursts of maybe 350w. The reason the 11t is really a problem is there just are not that many teeth to share the load. Lekkie makes a 52t chainring. Or get a BCD adapter that lets you use standard chainrings if you don't need the deep offset of Eclipse or Lekkie rings. That should let you stay off the smaller cogs. Question will be will you still have low enough gears for hills or wind?
        I appreciate the response. I realize that my second cog is 12t and it has never skipped, though it leads to an excessively high cadence at top speeds, so if I was to go with another cassette with a 12t high gear, I'm thinking that would go well with a larger chainring. Maybe a 50t or 52t. I did notice that the Luna Eclipse chainring face has a bit of an offset, don't know if it is needed or not, but when on the smallest cog it doesn't look like it is at much of angle if any. I never use my lowest gear now and I can't imagine that any 8 speed cassette is going to leave me wanting a lower gear even if I went with a 52t chainring.

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        • Mike_V
          Mike_V commented
          Editing a comment
          OK Lunie ! You got it dialed in for the Long Island terrain, quick. no need for the 11T and it may have run hot.
          Nice high power practical stealth eBike
          Custom painting might be nice or an 'attractive nuisance'

        #5
        Originally posted by 73Eldo View Post
        It sounds like you just may be exceeding the capabilities of an 11 tooth cog. Remember this stuff is designed for human power which is more like 250w continuous with bursts of maybe 350w. The reason the 11t is really a problem is there just are not that many teeth to share the load. Lekkie makes a 52t chainring. Or get a BCD adapter that lets you use standard chainrings if you don't need the deep offset of Eclipse or Lekkie rings. That should let you stay off the smaller cogs. Question will be will you still have low enough gears for hills or wind?

        I ended up going with a 52t ring that I found in China for much less money than the Lekkie. It has less offset than the Eclipse by far, but then the Eclipse has much more offset than the standard chainring that came with the kit. Go figure. https://www.ebay.com/itm/134546717292?var=434050858057

        I still don't use my lowest gear ever, will not climb a hill that steep or be out in wind that strong. LOL. Now I am avoiding the 11t cog and the 12t is working great. If and when I replace my chain and cassette again, I'll look for one with 12t as the smallest cog.

        BTW. I also started a thread on reddit and I go many more responses there, but yours it turns out was one of the more useful. Thanks.

        Comment


          #6
          I use a Park CC2 chain checker that put's an actual number on the chain wear. New KMC chains can come in at .5% stretch. This is where I replace my Wippermann chains which come in at 0% stretch when new. You might try another brand of chain. Wippermann is godawful expensive. May e YBN, or SRAM will be better. I thnk KMC makes Shimano chains. For this kind of use the CC2 is worth having. Zero Friction Cycling sells YBN, and they test a lot of chains so they're probably good.
          My theory is that what the chain measures on the workstand and what's happening under 1500W power are probably not the same thing.
          Last edited by Retrorockit; 09-18-2023, 03:19 PM.

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            #7
            Me I use a 8speed SHIMANO CS-HG400


            with this derailleur



            It is a 11-40t with a Lekie bling ring46t , FT chain ring , and a KMC 8 speed chain. and never has been a issue using any of my gears . When I had My 9 speed setup I used to get the same thing as You .
            I found it gave me a perfect chain line might want to consider these

            Comment


            • Retrorockit
              Retrorockit commented
              Editing a comment
              A lot of people use KMC without problems. But I prefer wax lubes, and getting the factory goo off of them is almost impossible, and Zero Friction Cycling says their coating rejects wax. So I don't run them for some other reasons But that is a good cassette. I'm running it too.

            • Dshue
              Dshue commented
              Editing a comment
              I've had no problem using squirt chain kube with KMC X8 chain. I had this problem just last summer, what I found was my derailleur cage was bent. Just hand cranking on the stand wouldn't cause it but under motor power with the brakes applied it would skip. Put it on a stand and watch carefully to see if the chain is trying to climb the next cog. I bet you'll see that it is.

            #8
            Originally posted by lunatic fringe View Post


            I ended up going with a 52t ring that I found in China for much less money than the Lekkie. It has less offset than the Eclipse by far, but then the Eclipse has much more offset than the standard chainring that came with the kit. Go figure. https://www.ebay.com/itm/134546717292?var=434050858057
            Let us know how the Gustavo chainring works for you. I stayed away from it after all the comments about the offset not being correct and causing problems. I went with the Lekkie 52t. The Lekkie ring has been excellent but I've broke a few of them. Seems my first gear(28t) has too much offset and chain angle so when I climb severe hills (1200+ watts) the side pull is hard on the Leckkie ring and will break the webbing in the ring. FWIW.....

            Comment


              #9
              During testing of the Zip Tie Mod I needed a chain guide that would put the chain straight onto an non offset chainring no matter what.
              ​ ​​ This chain guide came to be out of another DIY project here The Mid Drive Cassette Zip Tie Mod. This guide solved some problems peculiar to that mod. But also solved some more common ones too. AS you can see form the flat 50t chain ring and no Wide/ Narrow feature this bike has chain line issues. It might have been a

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                #10
                There are couple of little things to look at also. Watch the derailleur as the chain goes through. Does it kick a little bit at one or 2 points. This would be a tight chain link passing through. bending the chain sideways can loosen it up there (unless it's the tool less link) Also you may need not only a new shift cable but a new cable housing. Brake housing is like a coil spring, but shift housing has wires running lengthwise. The ends can rust and swell up changing what your shifter is doing at the derailleur end. Also the adjustment of the top gear is done more with the H limit screw than the barrel adjuster so play with that some.

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