Stiffer frame, tensioner or full narrow-wide?- Mtbr.com
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  1. #1
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    Stiffer frame, tensioner or full narrow-wide?

    Edit - if there's too much text below, just watch the video first. 100fps slow-mo of tight chain getting loose with frame flex...

    I've got issues keeping chains on my bikes. When powering up hills the frame flexes causing the
    bottom of the chain to become loose. If the hill is also rough the chain bounces around and often comes off the back cog.

    I started on a Trek Bruiser in 2003 and never had this problem - it was very stiff and nothing would cause it to flex :-) After riding that for a few years I wanted something a bit smoother and went for a steel 29er - this was a big disappointment (in the chain regard - really liked it otherwise) as part of the reason for getting it was that it was a real singlespeed and I'd be able to adjust the chain! (The Trek had a magic ratio of 38x18, hence my username, and spent a lot of time with the chain quite loose - but didn't drop it unless it was really worn out) Anyway, I just accepted that the KHS was a cheap frame and that it was going to flex and kept riding. After a while it broke so I looked around and found a Karate Monkey frame, moved over most components and did a few upgrades. The chain issues persisted - so much for a "good" frame. The Karate Monkey was also a tiny bit big for me so I kept looking - found a good deal on a Kona Kula. Chain throwing when climbing rough hills persisted :-(

    Now I was determined to prove my theory about how and why my chain had been coming off all these years so I borrowed a GoPro and mounted it on a bottle cage mount pointing down at my chain - recorded at 720p 100fps, playback at 30fps. I didn't manage to get the chain to come off while recording (Murphy's Law and all that..) but if you focus on the bottom chain run you will see it taught and not bouncing around as I drop into the bottom of a rocky creek and then go loose and flop about all over the place as I power up the other side. Ignore the creaking sounds - it's just the sliding drop-outs need some grease and greatly exaggerated by the slow-mo.

    As I see it I have 3 options:

    1 - try to find a frame that won't flex so much. Suggestions? Look at my gear history - I don't have a big bike budget!

    2 - add a tensioner of some sort. This is probably the most logical option but just does not "feel" right as part of my original reason for going singlespeed was the noise of the derailer banging about when I first bought the Bruiser.

    3 - go to a full narrow-wide drive train. This feels best to me, but I'm concerned that it won't be enough to keep my chain on. Anyone have experience to say that it will? Anyone know of a narrow-wide chainwheel for my 19mm spindle BMX cranks?

    Thanks for reading my wall of text!
    Last edited by 38eighteen; 12-03-2015 at 12:12 AM.

  2. #2
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    Does your rear cog have a tall tooth profile?

    What gear count are you running front and back now?

    Assuming your chainline is dialed in?

    How concentric is your chainring relative to the spindle axis? Is it possible that you have a loose spot?

    Also, if your dropouts are sliding, you're probably not maintaining tension. How tight is your chain?

  3. #3
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    I am sure my chainstays flex, but I don't have problems with my chain falling off except when I fail to tension the sliders on my frame to take up chain slack as the chain had "stretched" a bit. a good cog and a dedicated SS chainring should not allow the chain to drop if the chain is set up tight enough unless something else is going on.

    I don't think a narrow-wide ring will help. I only have a n-w on my bike because it sometimes run a 9 speed rear mech. if I was 100% committed to SS riding only, i would have no need for a n-w ring.

  4. #4
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    Quote Originally Posted by justin_amador View Post
    Does your rear cog have a tall tooth profile?
    Yes - the teeth are taller than the side plates of the chain.

    Quote Originally Posted by justin_amador View Post
    What gear count are you running front and back now?
    32x18

    Quote Originally Posted by justin_amador View Post
    Assuming your chainline is dialed in?
    Yes - checked and double checked many times. Clamp a small straight-edge to both the chainwheel and the cog (not at the same time..) and check that it's aligned to the chain for the full length.

    Quote Originally Posted by justin_amador View Post
    How concentric is your chainring relative to the spindle axis? Is it possible that you have a loose spot?
    Very. This has always been a frustration for me so I went and bought a nice Renthal sprocket (I like and trust Renthal because I used to also ride motocross and that's where they started) and that runs almost perfectly concentric.

    Quote Originally Posted by justin_amador View Post
    Also, if your dropouts are sliding, you're probably not maintaining tension. How tight is your chain?
    Drop-outs are not sliding - they have adjusting screws to keep them in place. Chain is very tight - maybe even too tight. When it's cold it binds a little, but once it warms up it runs OK. Even when warm there is zero free play.

  5. #5
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    Perplexing... never had that issue with SSing. Subscribed for the simple curiosity of the solution.
    I don't know why,... it's just MUSS easier to pedal than the other ones.

  6. #6
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    Neat video and kinda creepy with the sound and the backdrop.

    Not knowing how big or strong you are, I am fairly convinced it may not be the frame. What parts are common from the other frames to this one? Rear hub? Cog? Chain? And what is new? That seems really loose when it gets loose and wonder what the hub bearings or cassette drive is doing. I am not a big guy, but when my chain is looser (never dropped a chain yet) my chain would make the click like it was trying to jump the cog. More like a pop. Diagnosed with the help of an awesome LBS (Shadetree Bikes) that it could be my hub bearings having play laterally and radially. I popped in some new bearings and have yet to have the issue. Something to think about.
    Vassago Cycles, Shadetree Bikes, Flat Tire Bikes, Galfer Brakes USA

  7. #7
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    She-oot. Perplexing.

    I like cstem's thoughts on cog wear, chain wear, and bearings or cassette-hub interface looseness. Give her the ol' bottom bracket test and maybe see if you can feel any play in the hub or the rear axle (especially if you are running a cup/cone style). Can you flip your rear cog around and run that way for a bit and see if you get the same issue?

  8. #8
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    Curious - this is an issue that I've never experienced and I always ride a steel framed bike (Singular Hummingbird) which I'm sure flexes a fair bit. I'm not that heavy, mind you, (67kgs) so I suppose there's a limit to how much flex I can induce.
    What chain do you use - SS specific or a dérailleur type chain? I'm just thinking that if it's the latter and the bottom run does slacken a little under extreme load then maybe it's more likely to be deflected enough by bumps to come off the sprocket than a SS chain would.
    I don't run my chain super tight and occasionally, at the end of a long, muddy ride, there have been a few times where it's slacker than I would like but still I've never had a problem with dropping a chain. In fact, the only time I ever have is when a small branch got trapped between the chain and sprocket.
    So all this stuff like absolute concentricity of sprockets, while it's nice to have shouldn't make or break whether the chain stays on or not.
    Slightly distorted sideplates in one spot maybe or have you tried a different chain anyway?
    Try a different make of chain even - I can recommend KMC Z610HX.

  9. #9
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    What brand of rear cog are you running?

    The interesting thing about this is I happen to know that my frame flexes some too. I've never put a GoPro on my frame, but I've heard my chain bouncing around climbing hills. The only time I've ever dropped the chain on my current frame though was because of a hosed bearing in the BB letting the crankset flop around. My current crankset came with a NW ring and that hasn't caused any problems, but it did solve any either (of course, there weren't any problems I was aware of to solve - so there's that).

    I would say give a longer tooth rear cog or NW rear cog (does wolftooth make one?) a try with a NW front ring. It's a relatively cheap solution. As far as a frame that doesn't flex, any cheap, heavy aluminium frame should fit that bill. Of course, you'll also pay the penalty in ride quality.

  10. #10
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    My advice is to step up to a larger ring and cog. This is a good chance to get some new stuff. I am a big fan of Endless Cogs. Narrow/wide is a good idea but generally on a single speed they should not be needed.

    Size matters, 36/21 or 40/23 puts more teeth on the chain vs. 32/18 with just about the same final gear ratio. If your frame has room you could also step up to 38 or 40 in the front and use a larger cog in the rear. The bigger combos are less likely to throw due to flex and will generally run smoother all around.

    Also, make sure the chain is in good condition. Try a brand new chain when you install the new bigger ring and cog. Keep a few chains around, measure them often, discard your chains when the show wear and your teeth will last a long time.

    Good luck and let us know what you find.

  11. #11
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    Quote Originally Posted by febikes View Post
    My advice is to step up to a larger ring and cog. This is a good chance to get some new stuff. I am a big fan of Endless Cogs. Narrow/wide is a good idea but generally on a single speed they should not be needed.

    Size matters, 36/21 or 40/23 puts more teeth on the chain vs. 32/18 with just about the same final gear ratio. If your frame has room you could also step up to 38 or 40 in the front and use a larger cog in the rear. The bigger combos are less likely to throw due to flex and will generally run smoother all around.

    Also, make sure the chain is in good condition. Try a brand new chain when you install the new bigger ring and cog. Keep a few chains around, measure them often, discard your chains when the show wear and your teeth will last a long time.

    Good luck and let us know what you find.

    Sound advice IMO^

  12. #12
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    Well, you swapped frames and it's still happening, so that doesn't sound like the issue. Beyond that, the KM doesn't have a reputation for being a whippet -- I've heard the term "tank" a lot but haven't heard people griping about excessive frame compliance. Check out Jeff Jones' website, he has a similar video of chainstay flex on his titanium frames, that thing bounces around like a suspension. So I kind of doubt that's the problem.

    Bigger toothy bits will probably help, but 32/18 should be plenty big enough.

    Here's how I would approach it:

    1. Get your chain tension right, it doesn't have to be gorilla tight if your driveline is right.
    2. Check your driveline as in the FAQ. Critical. I don't like the straightedge technique, better to measure I think.
    3. Check your procedure for tensioning the chain. Rotate the cranks a bit while you're tensioning the chain. Use a torque wrench on your slideouts. Critical.
    4. Flip the bike upside down or put it in a stand, rotate the cranks, see how much chain tension varies throughout the cycle. If you read similar threads on this forum, apparently some variance is common. They say chainrings are never perfectly round. So don't let your OCD run away with you. But, if you think it varies too much, troubleshoot it:
    a) Worn chain. Note, doesn't matter what kind of chain you use, lots of people use 9 or 10-speed chain. As much of a cheapskate as I am, even I'll admit that a 10-speed Shimano chain is way nicer than the crappy 8-speed chains I've been using. Lighter and stronger.
    b) Worn cr or cog. Consider replacing all three (cog, cr, chain) if any of your toothy things are worn.
    c) Check for play between the cog and hub.
    d) Check for play in the rear axle. If present, rebuild the hub and see if it goes away. If the bearing races are worn you won't be able to fix it with a rebuild. (Next time don't run the chain so doggone tight.)
    e) Look at the cranks
    i) Is the cr round? Not sure how to check this but apparently this can be an issue (see http://forums.mtbr.com/singlespeed/u...ts-680545.html)
    ii) Check/replace bb
    iii) Center cr Singlespeed Bicycle Conversions
    iv) Consider possibility spider is off kilter.



    If you wind up replacing the hub, think about slapping an endless bike cog on there, that sucker is precision machined.

    If you're thinking about replacing the cr, or trying some different sizes, I've seen some awesome deals on Pricepoint. Also, this guy 32T Single Speed Chainring 104 BCD 7075 T6 Race Face Niner Surly Salsa Hope FSA | eBay believe it or not has really nice cr's, very close cr bolt tolerances, very light, price is definitely right. Although dang, that Renthal is bad-ass, isn't it? You don't need a n/w cr although if the rf cr's are on sale, the price is hard to beat, and the colors are pretty. Note a n/w cr rules out half links if you ever think that's an option for you. Don't buy cheap (BMX) cogs, they chew up your freehub body. Don't be sad; if you don't have a box of cr's and cogs lying around, you aren't doing it right.

    If you decide to replace your cranks, face the bb shell and think about a Hollowtech or similar, eg Shimano Deore (great value for the $) or a Raceface (super cheap on ebay but think about getting a Shimano bb). Something with a meaty axle.

    I kind of have to suspect when you transferred components from one bike to the other, you transferred the problem as well. How many miles you got on that drivetrain? Are those 12-year-old components? Might need to be talking to Santa eh

    I bet 5 cents it's your rear hub. Bet ya got some play in the axle from running your chain too tight.
    Last edited by TampaDave; 12-05-2015 at 08:47 AM.

  13. #13
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    I can see when your right leg pushes down, the chainring looks like it moves to the right some. Im speculating something with the bottom bracket and spindle causing it to flex too much. Was this the same set of cranks on your previous bikes as well? If so maybe try a thicker spindle crankset, 24mm and up. Not sure.

  14. #14
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    Thank you all - lots of great reading.

    There is no play in the BB - I'm paranoid about this and have triple checked.

    Looks like I'm investing in a new, bigger, drive chain.

    I'll let you all know how it works out.

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