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Quad Recument E-bike chain rings

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    Quad Recument E-bike chain rings

    This has my hair on fire.....

    I've 4-wheel fat-tire recumbent with a Bafang mid drive (1000) that came with a 38T front crank chained to a 38T motor crank shaft ring and a 46T stock bafang on the motor. It pedaled very smoothly but didn't have the low end I need for my hills.

    So I played around with several rings and ended up putting a 30T on the motor with works great when only using the throttle, but I can't pedal it - it feels like I'm fighting motor.

    I hope I can fix it my just replacing the pedal crank up front but can't wrap my head around whether I need to go with a larger pedal crank or a smaller. ??

    I hope I don't have the replace the motor crank ring as that's a custom part.

    Clear as mud? I'm thinking my parts vocab may be off but maybe these pics with help.

    https://www.utahtrikes.com/RECENTTRI...-Electric.html

    Thx, bob

    #2
    You need to look at both systems separately. Making the driven front ring smaller is the same as shifting to a smaller cog on the rear. To alleviate your problem you need a smaller ring on your crankset. Have you tried the 30t up there? The front system from crank to motor operates just the same as an ordinary multi speed bike. The rear system from the motor to the rear axle also operates just like an ordinary multi speed bike.
    The hardest gear to pedal is always the largest front(driving) chainring and the smallest rear(driven) cog. And the easiest to pedal is the smallest front chainring and the largest rear cog.
    Last edited by Dshue; 3 weeks ago.

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      #3
      No, I haven't but will, thanks Dshue.

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        #4
        I'm having trouble wrapping my brain around the whole layout of this thing. Those photos didn't help much. Is it actually from Utah or did someone build it to be like one of theirs? Just wondering if maybe the builder missed a key element of the design like an extra freewheel somewhere.

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          #5
          It's from Utah Trikes and the stock config was perfect for relatively flat riding. But I've been trying to gear it down to be better for my hills and now I've got a 30T on the motor. It came with the stock 46T bafang ring

          The rest is stock, 38T on the front crank back to a 38T for the outer ring on the motor (the motor shaft that your would put your pedal crank set on for a regular bike).

          So looking at as two systems like Dshue mentioned we got a 38T pedal crank up front that leads to a 38T ring on the motor's free wheel shaft.

          And we have a 30T (was a 46T) that leads from the motor back to the geared hub.

          I'm guessing there's a simple math solution on how to do this but not simple enough for me!

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            #6
            I'd try a 30 (or 34) tooth up front, as mentioned by Dshue - but it'll be more cost than just the ring, judging by that 5-arm crank spider. And yes, you will be fighting some motor induced drag, especially if that custom motor crank ring is not driving through the motor's spindle (but it looks like it does):


            Click image for larger version  Name:	DSC_5060-2.jpg Views:	0 Size:	153.1 KB ID:	116981

            Pedals to motor is currently 1:1 - 38:34 would be a 10% reduction, 38:30 20%.
            BBSHD/BBS02B builds: IGH 1 2 3 4 5 6

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              #7
              A bit more complicated than just changing out the ring on my KHS500. I'll let you know how it goes. Thanks all.

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                #8
                30T on the crank is working pretty good (good call Dshue).

                So, Ended up with the 30T on the crank back to the stock 38T on the motor shaft and an aftermarket 38 on the motor. Feels pretty well synchronized. Still want to try and reduce the 38 on the motor but am waiting for the weather to turn bad. Pretty mild fall so far.

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                  #9
                  You want bad weather? See how it goes through deep snow? That is one thing I am waiting for too to see how my last gearing change does. Its great for not snow but I am wondering how much the snow will slow things down.

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                    #10
                    No, not a huge fan of bad weather but those days are good days to spend in the garage tinkering. I have ridden in show though and I can tell you powder is not a big deal but wet snow takes a lot of power and it's tough to handle on a regular fat bike - at least for me!

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