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1x problem

JGTRJGTR Posts: 1,404
edited July 2017 in MTB workshop & tech
Hi all

Recently changed from 2x to 1x. Gone with 34T oval and 11-42 rear. Under heavy loaf (pushing up hill or riding with front brake on) whilst in the lowest (42) gear the chain jumps every so often.

It's fine on the 2nd sprocket in and have indexed it spot on twice now.

Could it be the chain is too short? Got new chain from shop, SRAM chain, and there is only about 10mm of movement left in derailleur arm when suspension compressed (20mm when not under compression. Below is a pic showing clearance when in highest gear....seems room left for more length in chain?? Shop sold me a 114 link chain (+ quick link?) which I though would be too short but they assured me it would be ok and I'd have to take links out, I didnt remove any links???

Any ideas?



  • Did you check your new chain length against the old one, or do the large-large cogs plus a link? (Alternatively try riding with something lighter than your heavy loaf, such as a baguette).
  • JGTRJGTR Posts: 1,404
    Couldn't check again old chain as it's a different gear set. Sizing wise was told lots of different advice. It was big/big plus a link - had also been told big/big plus 2 links and shop said size is on the small cog and just make sure there was just enough clearance between between the derailleur arm and the chain??! Going by the shops advice I could add links as I have quite an lot of clearance as seen in the pic....the shop I use is very good. On the big sprocket there is still a small amount of travel left in the derailleur but have also read that too much chain tension (i.e. Chain too short) can cause the issue I have??

    Maybe a trip back to the shop, they assured me I'd have to remove links (114 link chain) but I didn't

    Peanut butter sandwiches all the way!
  • What does the derailleur look like when in the lowest gear (picture please). Judging solely by the picture you provided, I'd tell you to shorten that chain. But having the right length for the largest sprocket is naturally most important.

    42T is a pretty big size, so you might be having issues with your chainline. Inspect it. Should be at least in the middle of your cassette, preferably closer to the largest sprocket (for a 42T sprocket, I'd definitely say closer to it). Chainline won't be that big of an issue on the smaller sprockets.
    Typically, when chainline isn't good enough, your chain will slip when backpedaling while on the largest sprocket.
  • JGTRJGTR Posts: 1,404
    I can't remove any links, derailleur is nearly at full extension. I have spaced the chain ring in so that the chan line is 50mm which is within what it should be but maybe 42Tneeds more? I think I can swap spacers from one side to the other on the crank to see if it makes any difference. The chain does come off when I back pedal which isn't an issue when I'm riding, and it is because the chain line but this is a common side effect of fitting wide range cassettes so I'm told.
  • It's common side effect but one that can often be remedied by moving the chainline closer to the frame - that is, if the frame allows for moving the chainrings closer in.

    I have to ask, is your derailleur a middle or long cage? Not always clear just from a picture.
  • JGTRJGTR Posts: 1,404
    It's common side effect but one that can often be remedied by moving the chainline closer to the frame - that is, if the frame allows for moving the chainrings closer in.

    I have to ask, is your derailleur a middle or long cage? Not always clear just from a picture.

    Pretty sure it's long cage


  • I've never worked with SRAM mech of this make, but all the Shimano mechs I've ever seen can go pretty much horizontal (not saying you should run them horizontal). In other words, if I saw this on my bike (with my derailleur), I'd definitely shorten the chain (unless that's picture without compressed suspension).

    Anyways, back to the chainline, if that's where it is (last picture), try moving it closer to the frame if you can. For the purpose of testing it, use whatever you have at hand to see how far you need to move it before actually getting some spacers for riding use.

    BTW, did you try messing with b-screw and setting the limit screw a bit further in (mech closer to the frame)?
  • JGTRJGTR Posts: 1,404
    Started from scratch, set B screw so that there was 6 mm between big cog and top jockey wheel, L & H screws, cable tension etc. Index is spot on and no issues with shifting. B screw just seems to adjust the clearance between jockey wheel and cassette? Can it be used to move mech closer to frame?

    That pic is the derailleur at pretty much full extension.....with the suspension compressed there is on 10mm of extension left on the derailleur.

    I'll try moving the branch across, have probably got 10 mm to play with before chain ring fouls frame.

    I see why chain falls off when back pedaling as the chain line causes it to fall off but when pedaling forward the derailleur slings the chain to the cassette? It could be that because the derailleur is nearly at full extension there is too much chain tension but don't understand why this would cause the chain to miss a few teeth on the 42t every so often when pushing hard?
  • B screw does pretty much what you say it does. Moving the mech closer to the frame is done by the limit screw. Probably worth checking out whether messing around with those settings can fix the problem. And yes, the chain falls when pedaling backwards because it is no longer being pressed against the cassette.
    If the mech is really set up correctly and both your chain and cassette are new, something else has to be wrong. Best to eliminate easy to do stuff first. Try adjusting the chainline (because that could at least fix the backpedaling issue), check for any stiff links (probably would notice on all gears though).

    Or as with everything, if it's too much bother, you can admit defeat and bring the bike to the shop :D
  • JGTRJGTR Posts: 1,404
    Could be the b screw, I'll try fine tuning and eeking some more movement out the derailleur and checking for iffy links, may be the power link??
  • When there's something with the chain, It's very rarely the powerlink. It would happen very consistently. But hard to eliminate any possibility from my side.
    Also, you've got a clutch. Try turning it off. I just checked to be sure I'm not making anything up but my derailleur can move all the way up and touch the chainstay. I've never worked with a clutch so I have no idea if it could interfere in any way, but I understand they're also adjustable.
  • The RookieThe Rookie Posts: 27,756
    Depending on chain growth with suspension travel that looks like you could loose another pair of links.

    Setting is simple, let air out the shock so it's at the ride height for max chain length and then big/big (not through the rear mech) and overlap by one pair.

    Check the high stop isn't just easing it off the biggest sprocket, a rear photo in first gear showing mech cage alignment to the cassette would be good.
  • JGTRJGTR Posts: 1,404
    Update, seem have to sorted this, adjusted b screw and gave it some more movement, seems ok on test ride, have to see how it goes on proper ride
  • Hello guys. Just a quick ressurection of the thread. So, I've been riding a 1x10 since january this year. No issues. SC 32T NW front, shimano SLX 2x crank, and sunrace 11-42 cassette with a XT mid cage RD.

    I bought some carbon cranks just for the fun of it (s2200, or rebranded X0, as you wish), and I had the possibility to select the spider I want. Since I had a brand new 34T oval 104 bcd ring, I asked the seller to give me a 3x10 spider with 104 BCD.

    When I mounted the 34T on the position of the middle ring, my chainline was way of 49mm. I mounted it on the outer ring's place, and I got spot on 49mm. With that chainline, my chain is perfect with my 5th cog, a bit deflected on 11T and a bit more deflected on 42T. If I switch my ring to the middle position.. the chainline is about 43/44mm, and the CL is inversed. It's about inline with the 5th cog, but more deflected at 11T, and a bit less on 42T. Hoping this would change.. I ordered a direct mount ring of ebay, and I didn't pay attention, so I got a GXP ring with 6mm offset. I have a short spindle drive, so I need a BB30 ring with no offset.

    The issue that came up is that with that 6mm offset, my CL is the same as it was on my middle ring on my spider... 49mm. Which is perfect. BUT if I get a BB30 ring, the CL would be 43ishmm which is not good (in theory).

    So to cut this post short....

    What is better? to have a more deflection on my 42T or at 11T? I obviously can't have both, but I believe that it would be better to have less deflection on 42T since I ride a lot of uphill sections, and the chain is under more stress while pushing uphill than down or straight. That's why I don't get why should the 49mm CL bi better that 43mm??

    If it is better, then my GXP NW is great, but the manual says i need a no offset ring ( which in turn messes up my CL)...

    I'm baffled... local riders say I overthink that, and I need to select my CL in co-ordinance with the type of terrain I ride... more uphill or more long straights....

    what are your opinions?
  • The RookieThe Rookie Posts: 27,756
    Minimise the biggest deflection, sprocket size has no effect as both come off a tooth at top dead centre (near as dammit) before heading for the chainring.
  • The Rookie wrote:
    Minimise the biggest deflection, sprocket size has no effect as both come off a tooth at top dead centre (near as dammit) before heading for the chainring.

    that is the problem.. if I minimize the deflection on the 42T cog, i have a big deflection on 11T, and vice versa.. I can't have both....
  • The RookieThe Rookie Posts: 27,756
    The Rookie wrote:
    Minimise the biggest deflection
    With added emphasis, use the one that gives the smallest value for the biggest deflection, MEASURE as different hubs put the cassette in different locations.
  • Oh.. I see. When I get a new chain, I'll see what will I come up with. I have a 240s 135mm hub.
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