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As the cogs in cassette seem separable, can it be converted into single speed by just putting the 9 identical cogs of the gear you like and retaining the rest of the gear mechanism as it was?

Such a cassette should theoretically last much longer, as you simply shift to another cog when one is worn. It may also be lighter if the weight of the selected cog is below the average.

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  • 5
    If the only time you're taking your rear wheel apart is to change a worn cassette, you might want to think about your maintenance schedule a little more strongly.
    – throx
    Commented Dec 7, 2021 at 3:19
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    Don't get 9 seperate cassete cogs, get some spacers and a single hyperglide splined cog like those offered but Surly. Alternatively, it sounds like a fun experiment if you can access the cogs for cheap. Just try it, see if all the naysayers below hold any currency 😆
    – Lamar Latrell
    Commented Dec 7, 2021 at 7:19
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    It would be easier to set the limit screws so that the derailleur can't be shifted.
    – EvilSnack
    Commented Dec 7, 2021 at 15:08
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    If you want single speed why would you not just remove the derailleur and all the complexity around it and put on a single cog??
    – R.. GitHub STOP HELPING ICE
    Commented Dec 7, 2021 at 16:46
  • 8
    What about simply refraining from changing gears ? Zero cost, effective immediately, essentially the same effect ;-)
    – Vincent Fourmond
    Commented Dec 8, 2021 at 18:18

8 Answers 8

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Since 1982 or so just about all rear derailleurs are built with a slant parallelogram design so that it glides in a diagonal line as it shifts up and down. This is supposed to keep the jockey wheel a constant distance from your cogs, which are arranged from biggest to smallest. It is a very popular design because it just works really well and the patent lapsed in '82.

If all your cogs are the same size, as you shift out towards the outside of the bike your derailleur tends to get closer to the cogs (since they are all the same size).

SO: To make this work well you will probably need to find a rear derailleur that is not a slant parallelogram. These exist in some very cheap designs. I think this hack is absolutely worth it, if only for the lolz.

In order to get all those cogs you may have to cut up old used cassettes. You can buy separate cogs using Miche system as well but it will be more expensive.

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    This is actually the answer I was looking for - why? Many other answers tell this is not gonna work, but I was unable to understand where is exactly the problem.
    – nightrider
    Commented Dec 8, 2021 at 8:14
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I would say : no way.

The rear derailleur is not supposed to handle cogs with the same dimension. The cogs should be smaller towards the outer part of the cassette, to correspond to the movement of the RD.

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  • And even if one wanted to do the shifting manually, it still is an issue, because the RD holds the chain at the right sprocket and guides the chain through the pulleys. One would have to readjust the cable tension for each change of the sprocket and there probably would not be enough leeway.
    – Vladimir F Героям слава
    Commented Dec 6, 2021 at 21:51
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    Also, bikes are made to have smaller cogs nearer to the frame. There's a limit to the number of teeth you can have on the outside cog before the chain rubs against the frame. If you like the smallest cog you can convert your bike to a single speed by disconnecting the derailleur cable. You might even be able to choose one of the larger cogs by adjusting the limit screw on the derailleur. I've done this as a roadside repair for a broken cable.
    – Rich Moss
    Commented Dec 6, 2021 at 23:49
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    "An escalator can never break: it can only become stairs. You should never see an Escalator Temporarily Out Of Order sign, just Escalator Temporarily Stairs. Sorry for the convenience." - Mitch Hedberg
    – Rich Moss
    Commented Dec 6, 2021 at 23:52
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    @RichMoss Funny but not entirely true. If the brakes fail unsafe (which they admitttedly shouldn't) or the chain breaks, it's going to be Escalator Temporarily Inclined Treadmill.
    – TooTea
    Commented Dec 7, 2021 at 7:10
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    @RichMoss ""An escalator can never break ..." You've never ridden the Washington DC Metro system, I see. Not only do escalators break, they magically disassemble themselves and stay that way for years...
    – Andrew Henle
    Commented Dec 7, 2021 at 14:16
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Additionally, you'd have to have at least one different cog, probably an 11 or 12 tooth outermost, because it has a differnet design to every other cog.

This little cog also has the detents for the lockring to engage into, and without them the lockring could back itself out letting all the cogs flop around somewhat. This would give sketchy riding at best.

Also, a singlespeed rewards a good chainline. That means the chain goes straight-into/out of the chainring and cog. By being out of line, you're wasting power, adding wear, and removing the chance to use chunky 1/8" chain instead of flexy 3/32" chain like derailleur bikes have to use.

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  • That is a non-issue, all can be 12, as I commented to AndyP. Then you just the appropriate chainring.
    – Vladimir F Героям слава
    Commented Dec 8, 2021 at 19:51
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    @VladimirF you miss my points. One cog would be in line with the chainring. All the others would need to bend the chain sideways.
    – Criggie ♦
    Commented Dec 8, 2021 at 22:35
  • @VladimirF and my other point is that the outermost cog would have to be 11 or 12, and of the design to "cap" the cassette on the freehub.
    – Criggie ♦
    Commented Dec 8, 2021 at 22:36
  • That's exactly whaat I was pointing out in my previous point to AndyP, that the real issue is that one would have to only use cogs with11, 12 or 13t. But I do not see have that prevents the "cassette" to have all cogs the same. Just make all of them 12t. OK I was probably wrong that one could use 11t, those come only as the outer ones, but 12t or 13t can be both out and inner.
    – Vladimir F Героям слава
    Commented Dec 8, 2021 at 23:09
  • Otherwise I did actually understood your chainline point, I just did not touch it at all, I commented solely on the longer part above the horizontal line. I just did not find it that important.
    – Vladimir F Героям слава
    Commented Dec 10, 2021 at 21:39
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It would still be a 9-speed. Each of the 9 would be 9 instances of the same speed.

You can get spacers for installing a single sprocket on your freehub. Also, rvil76 makes an important point about shifting.

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It may work, but why would you? Yes,technically it would be a single speed, but the reason for having a single speed is, as far as I know, to have a bike that is as light and simple as possible. By making a "same speed" rear cassette you would get (at least nearly) the weight of a 9 speed and all the complexity of a 9 speed without the flexibility a multi speed bike gives. So this would give you the worst of both parts.

On the other hand, if this was something you thought about doing just for the joy of doing something weird, just feel free do do it and probably learn a few things on the way,

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No.

Primarily because most cassettes are not actually fully made of separate cogs and the top few are usually a single piece.

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    That is hardly the primary reason because one can always buy those that are indeed composed of individual cogs. Or just remove the rivets that connect some of the connected sprockets, they are not really necessary, they are mostly for convenience. The real issue would be finding such cog size, that would accept the lockring. One would be mostly limited to 11, 12 or 13.
    – Vladimir F Героям слава
    Commented Dec 6, 2021 at 21:50
  • My cogs are all separate. Probably depends.
    – nightrider
    Commented Dec 10, 2021 at 7:57
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I think the closest you'll get is to just have a cassette comprising the biggest three cogs (which are usually joined), and then the rest of the space for the cassette filled with spacers.

The photos of this hill climbing bike demonstrate it: https://webcache.googleusercontent.com/search?q=cache:mgm6Li4DdToJ:https://cyclingtips.com/2020/08/6-2-kg-three-gears-and-cut-off-drops-the-bike-used-for-the-everesting-record/+&cd=11&hl=en&ct=clnk&gl=uk (you may have to scroll down as the top of the web page seems to be a big blank white space).

"[This time] I removed most of the rear cassette just leaving the 25-, 28- and 32-tooth sprockets.” The rest of the freehub body was filled with aluminium spacers commonly used for single-speed conversions."

I don't know why you'd want to do this (except for in extreme circumstances such as wanting a bike to set a hill-climbing record!).

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Just adding another reason why this may not work.
All cogs sit outside the vertical plane of the wheel. Any force you apply to the cassette will (very slightly) bend the axle.
That force has most effect on the cog that is farthest from the wheel. But as that is usually the smallest cog, that effect is reduced.

When you replace the farthest cog by a much larger one you risk bending the axle.

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  • This would be the most obvious for the big climbing cogs but who knows. If may favorite gear is 14 teeth, this may probably still work.
    – nightrider
    Commented Dec 10, 2021 at 7:56
  • It's actually the opposite. The axle is fixed at ends, so pulling it at the center would give most leverage to bend it.
    – ojs
    Commented Dec 10, 2021 at 13:51
  • How silly of me, I missed that. The cassette is indeed within the attachment points.
    – Jeff
    Commented Dec 10, 2021 at 13:56

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