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    Problems with SRAM NX Eagle (12×1) on a 20 inch wheel cargo bike

    I just replaced the drivetrain on my Xtracycle 27d. It's a longtail cargo bike with a 20 inch rear wheel. I put a new bottom bracket, cranks, derailleur, chain, cassette, and shifter. I built a custom wheel with a G-Sport BMX rim, 13 guage spokes, and shimano XT hub. I put a Schwalbe Marathon 365 tire on the rim.

    I'm running into problems.

    1. I can't shift into the 3 largest (easiest) gears. The derailleur contacts the tire.

    2. The bike autoshifts sometimes when going over a bump or pedaling hard. It did this with the old drivetrain too.

    —

    What should I do? Here are my thoughts so far, but I'd really like advice

    1. Easiest – just put a smaller tire on the back.

    2. Does the autoshifting always happen on longtails? My frame isn't obviously cracked, but you can feel it flex, especially with a passenger.

    3. If I had a shorter cage derailleur, it wouldn't overhang the rim and be less likely to conflict with the tire… But slack chain. Have you ever seen someone put a second dynamic (like a derailleur) chain tensioner on a cargo bike?

    4. How else could I get my bike more useable?

    by paddy_m

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    9 Comments

    1. Wise_Code5804 on

      Maybe this configuration just isn’t compatible? If you had room. That’s a MTB group set. It’s not designed around small diameter rims.

    2. bramski on

      What was the drivetrain before? The fact that the derailleur is in the same vertical space as the tire is a huge problem. Lean the bike over in a turn far enough and it could hit the ground when you get into the largest cog. That derailleur arm will go even lower when you go to the biggest cog.
      I’m guessing this was a 2x before? I think putting a 1×12 on a cargo bike is a terrible idea honestly. So much hassle.

    3. Sirwompus on

      First problem I think you just won’t get it to work. Second problem is probably because it doesn’t use full housing. Can you run full housing from the shifter to the RD?

    4. artemkrivonozhko on

      Maybe a planetary hub? Depending on your budget it might be either Nexus/Alfine or Rohloff. Might be a good choice for a cargobike

    5. toddlikesbikes on

      Dumb question but did you check the dish? Is that rim definitely centered on the hub?

      Really getting crazy here, but along with a smaller tire if your frame has room you can center the rim over the flanges (or even dish to the left) to snag a few extra mm.

    6. MacTally on

      To get some more clearance you could swap to a 10-44 cassette and buy a short cage for the derailleur.

      I’ve done this but with shimano to get more clearance with a 26″ trail bike to help avoid rocks etc.

      A quick search says sram should work the same in this case.

      Edit – Nevermind the 10-44 would need a different derailleur.

    7. contrary-contrarian on

      I don’t think NX eagle works well (if at all) with non-boost spacing hubs? Even if the derailleur didn’t contact the tire you still may have trouble.

      You’re gunna need to find a more compatible group set to put on there.

    8. MadamIzolda on

      I’m running the 1×12 NX and it already looks like a joke on 29 inch nobbies, and I’m afraid not much can be done. Might cut off a cm or 2 if you run a chain too long, but that’s about it

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