front sprockethey i am new here and i was just wondering if anyone can help me out with the problem of my chain keeps slipping when i pedal a little bit hard. I took my bike to lbs and they said that my chain was fine and the sprockets were near new if any one can help me out that would be much appreciated.front sprocket

[back sprocket and tensioner[2]

  • From what little I can see of he rear cog, it looks like it's worn out. Apr 7, 2016 at 11:57

3 Answers 3


That chain is sitting quite well on the front ring, almost perfectly, as far as can be discerned in the photo. In particularly, it doesn't appear to be elongated at all, which is usually the telltale sign of chain wear. When a chain is elongated, you can easily tell on the front ring, because it has so many teeth that the cumulative error of the elongated links causes it not to sit properly all the way around the ring.

I'm guessing you (or a previous owner) replaced the chain, possibly more than once, but didn't swap the rear cog at the same time.

That's a mistake.

Chains elongate as they wear, and at the same time, they wear the cog, and are worn by the cog. A chain which wore together with the cog might not skip, yet if you change to a new chain, that chain will skip on that old cog.

I've never been able to change a chain alone, without skipping cogs. (That is, the few times that I tried, before I stopped doing that).

Do check the tension! But note that chains don't have that much tension in derailleur systems (just that tension provided by the tension wheel) yet they don't skip, when in the proper condition. Basically there has to be ridiculously low tension. It's hard to tell from your picture, but it does look as if the chain is coming from the ring in a fairly straight line, no sag. Anyway, when you're pedaling hard, there is tension in the top section of the chain, between the ring teeth and the cog. Under this tension, they stay engaged even if the returning-to-ring section of the chain is sagging. If you don't believe me, think about this: when you remove a cassette from a hub on a derailleur system, you open a lock ring, for which you require a chain whip to hold the hub steady. That chain whip is just a piece of chain connected to a lever, loosely wrapped one of the cogs in the cassette: no tension in it at all, other than the applied tension. Nothing pulls on the unattached end of the chain to keep it wrapped around the cog! Yet, it grips tenaciously, enough to remove a stubborn lock ring. I've never had a chain whip skip, even when ridiculous force was needed (enough to break a spoke).

Get a new cog!


My guess would be a lack of chain tension. Is there too much chain length on that single-speed conversion?

You would want to run it - with the minimum amount of chain - and then use the chain tensioner to remove any remaining slack.

  • if i make the chain as tight as it can go it takes a really hard pedal but it will still slip and when it slips it makes the chain become loose again Apr 6, 2016 at 9:29
  • Just a guess, but it looks like the bolt on your chain tensioner is designed to work a bit like a sliding dropout. If that bolt isnt tight enough it will slide up the slot causing your chain to lose tension.
    – Andy P
    Apr 6, 2016 at 10:25

You have (at least) two problems.

  1. As you can see from the wear marks on the tensioner fixing bolt (the lower one), something is forcing the tensioner to release the chain. That suggests to me that you're catching the chain on something, because there's quite a bit of force required to scrub off the anodising and get back to bare metal on the tensioner. I would look for damaged teeth on the chainring and cog, and think about what you did just before the chain came off.

    1. You may find that chainring guards/guides help with that (decent metal ones, not plastic), they work both as bash plates and chain guides.
  2. You don't have much wrap on the rear cog. Derailleur bikes try for about 180 degrees, singlespeeds can get away with less because they have more chain tension. You don't have either. I had a chain tensioner like yours, and it sucked just like yours does.

    1. I replaced mine with a spring-loaded one. You should still try to increase the wrap if you do this.
    2. If you can take a link out of the chain that will help. You might even consider a half-link.
    3. A worn chain will ride up the teeth under pressure and if the tensioner isn't tight enough it will fall off. A new chain fixes that.
    4. likewise, a worn cog can drop the chain or if it's worn enough to have hooked teeth, a new chain can get caught up and you get rear-end chain suck (rare, and I can't imagine that getting enough force to shift your tensioner)
    5. you might be able to run the chain over it instead of under, to get more wrap. I couldn't do that because it hit my chainstays.
    6. Another option would be to see if you can get horizontal dropouts for your bike. Your dropouts are replaceable, and if you're lucky they offer both vertical and horizontal ones.
  3. Chainsuck. You have it/have had. I don't know if that happened before you switched to single speed, but it may indicate bent chainring teeth or bad chain alignment if it happened since you switched. Chainring guards will help here, or an anti-suck plate. But you shouldn't need either if the chainline is right and all the teeth are straight and not too worn.

Finally, I would check for wear on your chain and rear cog. The chainring looks fairly new, but I can't see the teeth on the cog in these photos. A worn chain could be the root cause of all your problems.

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