Mechanics and Fixing Any Questions Answered

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  • @PhilDAS after a couple of hours asking myself these same questions and feeling like I was trying to put a triangle into a circle hole, I think I cracked the case when I googled the cassette lockring I had laying around and found out that it’s made for a 12t small cog only. You guys had any experience with that?


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  • Sorry to ask a repeat question, but this is really bugging me because the problem reoccurred today and I feel it is only a matter of time before it happens when a car is just behind; opinions would be really welcome (or if this is the wrong thread to ask in, do let me know where I should go!)

    The first incident was when I was commuting to work and all of a sudden heard a bang, like as if my wheel had gone into a pothole or my pedal had scraped the floor. But neither of those seem to be it because there were no significant potholes on the road and I was going straight.

    My saddle had been turned 90deg sideways under me (like as if the bike had suddenly fishtailed while I was still seated, with the seatpost just slightly loose enough to move given sufficient force) but I thankfully remained on the bike and guided it to a stop. I found that my rear wheel was slightly mis-aligned and hence pressed into one side of my brake calipers, but when I shifted the caliper and spun the wheel to check, it spun freely and didn't seem out of true in relation to my chainstay.

    Turned the saddle back round, got back on the bike and cycled the last 5 minutes to work completely uneventfully - and made the commute home absolutely fine like as if nothing was wrong, at the end of the day.

    Happened again when I was going on a straight road, heard a bang/pop and fishtailed, came unclipped, rode my top tube for a while before braking the bike to a stop. Checked the rear end, no diagnosable issues.

    Just today I was making a slow turn onto a road from a pavement, again heard a pop like as if my rear wheel had gotten jammed, and came off the saddle onto the top tube. Went into the wrong side of the lane but thankfully it was a quiet road so the oncoming car had plenty of time to see me and slow. Got back on the bike, checked the rear wheel was spinning freely, then made the rest of the commute just fine.

    Pics of the rear end attached; it’s a fixed gear conversion so I have 0 idea what could have happened, because:

    • at first I thought it might have been the mudguard getting jammed in the wheel, but I can’t seem to replicate the issue (the mudguard flap coming in just rubs the wheel rather than jams it) and there is a good amount of clearance, not to mention it should have popped off if it was really jammed given it’s only held on by a rubber strap
    • Nuts are done up fine and chain tension remains normal and wheel aligned (at least as of the second and third times) so that does away with the wheel slipping in dropouts.
    • Spoke tension seems fine
    • Chain was changed less than 1000km ago and cog hasn’t seen more than 300k
    • lock ring on cog seems nice and tight
    • No visible cracks on any of the tubes, though I don’t know what I’m looking for..

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  • Stiff link in the chain? Might be doing something weird
    Does it do the same thing if you run it on the freewheel side?

  • Seems very mysterious to me. The only time anything similar has happened to me was when track nuts weren't done up tight enough. The rear wheel would end up jammed against a chainstay. But if you are finding your rear wheel still centered then I would guess that it's a drivechain issue.

    The only thing I can think of is that perhaps the chain managed to swing inboard, or was nudged by your foot, such that the tip of the chainring got caught under the edge of the chain link plate. Like halfway towards derailing the chain. This would lock up the drivechain instantaneously.

    Did you feel the cranks lock up at the time?

    Also can we have a closer side view of the front chainring?

  • Yeah stiff link is a good shout too but as there's a quick link in the chain I thought it was unlikely.

    Still worth checking.

  • replying to myself, where can i go to get 5mm machined off my hub end caps to make a 20-15mm conversion work ( non boost)

  • Will grab a picture of the front chainring tomorrow, thanks both for the input! How do I check for stiff links? I could try running it free for a bit (reluctantly) but I can’t replicate the issue even if it’s fixed, and it’s occurred about once every two weeks or so with daily commutes to multiple places?

    The cranks definitely did lock up momentarily, hence coming unclipped each time, but given it’s fixed presumably that would have happened regardless of whether it’s the wheel or the chainring locking up?

  • If you’re just looking for a bike workshop Winston at Varonha cycles down at Hither Green has done wonders for my bike forks so I presume machining a couple of parts would be a breeze (albeit replacing headset bearings in a slightly dodgy fashion, so mixed reviews there).

  • To check for stiff links derail the chain and then use your fingers to try to bend every link in turn, see if any are stiff.

  • Is this chain ring compatible with my Sram Force 22 bb30 chainset?
    I'm not sure what the 2 pin refers too.


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  • What is the chain line like I. E. If it is a conversion have they got a decent chain line with the rear cog in line with the front?
    Or is a small stone/chip getting stuck on the tyre and carrying around to get jammed under the mudguard and/or brake caliper?
    Given the decent weather why not run it without the mudguards and see if that helps.

  • How are the rear hub bearings? Have you tried removing the chain and spinning the wheel? Bearings could be momentarily seizing.

    Your chainring also looks worn in the first photo.

    I’d ditch the guards, try a different chain & chainring, and maybe sprocket.

  • It will be fine, two pins so it fits cranks with either hidden, or non-hidden 5th bolt.

  • Your lockring seems to be hanging off the outside of the hub somewhat which might something going on with the cog which in turn could cause a chainline issue.

    Could also be the cog sort of jumping between being tightened up against the shoulder on the hub from driving to backing off against the lockring under braking. When the cog is backed out against the lockring they will jam together and so everything can appear to be tight but as you push on the pedals the cog will release from the lockring and spin freely until it hits the shoulder on the hub then vice versa.

  • Thanks so much for all the helpful ideas! In response to the comments so far:

    • Will check for stiff links when I get the time to pull the bike apart, but I would have thought stiffness should be far more evident on regular use rather than occurring once every so often?
    • Chain line is fine (or at least I haven't had issues with it and when chain and sprocket are new bike is entirely silent) - running a 120mm hub with spacers in the dropouts. Might add that bike has been running fine for a year and a half prior to the problem surfacing!
    • Rear wheel spins fine, freely and noiselessly; what do seized bearings feel like?
    • Could be stones carrying all the way around but both the tires I was running (Schwalbe Duranos and now Zaffiro Pros) don't have much in the way of tread to catch something all the way around..
    • Would run without mudguards but this is my commuter so slightly defeats the purpose if I can't use them!
    • I use one of these lockrings (https://www.halowheels.com/shop/spares/h­ub-spares/fixed-sprocket-lockrings/) which has a recessed section (unless I was somehow meant to install it the other way..). I did check both the lockring and cog and both are on fairly tight. Was thinking about the cog jumping but in each case the spinning should be in the direction of my pedaling - so surely it should feel almost like the float you get when you're between engagement pawls on a freewheel, rather than a resistance which jams the wheel?

    Chainring is the only thing I haven't really thought to change.. more detailed pics attached! Come to think of it, this problem seems to only have surfaced after I changed out the chain (worn cog) then the cog a month later.. But both are 1/8; chain was new and cog still loads of life left, if that helps.


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  • the spinning should be in the direction of my pedaling - so surely it should feel almost like the float you get when you're between engagement pawls on a freewheel, rather than a resistance which jams the wheel?

    Not necessarily, pedalling can tighten the cog against the hub leaving it some space to undo until it hits the lockring and jams again and it can tighten itself thoroughly enough against both the hub and lockring that the movement isn't immediate. Like, it'll jam so tight against the hub that you can get a bit of resisting the pedals before it breaks free and then conversely it jams so tight against the lockright that you get a bit of pedalling before it breaks free.

    I don't know that this fits with what you are describing though, when it's happened to me it's a rather soft feeling, what you are describing sounds harsher.

    Looking at the photos you've posted 2 things strike me,

    1. There's a bit of paint loss on your chainstay around where the end of the spider would pass, is it possible that the crank arm (or a bulkier chainring nut) is contacting the chainstay here when you're riding and get a bit of flex?

    I don't think this is very likely btw as the paint loss doesn't seem bad enough for this.

    1. I think this one is more likely, could the top/front of the mudguard be jamming between the brake caliper/brake bridge and the tyre?

  • I have a click sounds which like its coming from the cranks. BSA bb on Quarq carbon cranks in a moots vamoots. Only happens when Im out of the saddle and above 300w and seems to be at a regular point in the pedal stroke.

    Ive regreased the pedals, greased cleats, tightened shimano QRs, replaced the bb, checked the frame for cracks, greased the point where the spokes cross, replaced the chainring bolts. What am I missing?

  • Chainring off, clean the spider and chainring mating surfaces*, dab of grease and reassemble.

    *clean could mean a wipe with a dry rag, that plus a squirt of degreaser, or something more abrasive if there’s corrosion or flaking paint or plating.

  • greased the point where the spokes cross

    This is a new one!

    Maybe also try a different set of pedals to remove them as the source?

  • This is a new one!

    Can be a problem with flat bladed spokes.

  • Ah ok.

    I’ve certainly seen noise from round spokes rubbing against each but usually a lack of tension would be the cause, never thought about the possibility of it occurring in a properly tensioned wheel.

  • Thanks the the advice - the qr needed greasing. Of course I found that out having done everything else

  • Dan of grease

    Say what?

  • He went by Danny.

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Mechanics and Fixing Any Questions Answered

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