Rebuilding to single speed

[PillowOnChest]

Hello! I am brand new here and with tinkering bicycle as well. I am posting here (Mod Edit: moved to mechanics, you'll get answers faster) in order to ask for experienced advice. I recently bought what I thought was a single speed bike, but which turned out to be a multi sprocketed bike with no gear-shifter. So in a sense it is single speed, except that when I drive the chain often jumps down the sprockets, ending up on the smallest, and sometime getting stuck between the cassette and the frame. Therefore I wish to modify the full cassette to a legit single speed sprocket with 'tall' teeth. Is this even doable and where do I start? I have attached some photos which I really hope can provide ample information. Thanks a lot in advance for answer, and sorry if this is inappropriate on your forums - then just do delete please!

 

[C R]

I have no experience of this, but I have read about people making the modification. As I understand you can get a single sprocket that will fit on the freehub in place of your current cassette, and use spacers to position the sprocket in line with your chainring. I presume that you have only one chainring. The other issue is managing chain tension, but your bike already seems to have the right dropouts and screws, so that should be straightforward.

Oh, and to cyclechat.

 

[Big John]

Condor cycles do a single speed conversion gizmo that fits onto the freehub. Not expensive either. My guess is you'll need a single speed chain too.

 

[ColinJ]

My singlespeed project...

I took a couple of old cassettes to bits and used one of the sprockets at the back, plus a pile of spacers to hold it in place. By carefully selecting the number of spacers either side of the sprocket, I got a perfect chainline.

The chain tensioner shown (as supplied) pulls the chain down to tension it. It uses a spring to create the tension. I found that the tensioner arm bounced about on rough roads and I kept unshipping the chain. I bodged it by removing the spring so that I could use the tensioner to push the chain up instead. I added a thick washer on the mounting bolt which allowed me to adjust the tension manually and then tighten the tensioner in that position.

Getting the chainline perfect is important. My chain kept falling off until I got it right. I do find the chain tensioner slightly irritating though. It makes an otherwise silent transmission slightly noisy.

I am thinking of trying a half link on my singlespeed bike. A new chain doesn't really need the chain tensioner. After a few hundred kms of use a fair amount of chain tensioning is needed. I reckon taking one full link out of the chain at that point and replacing it with a half-link might take up the slack.

(The chain runs quieter when the tensioner is slack and the chain is running almost straight.)

I think that idea could be made to work on your bike @PillowOnChest. You will have a small amount of adjustment in your dropouts and could adjust the chain length to get ideal tension, possibly by adding a half-link. You want to have the chain no looser than in my photograph above, and ideally slightly tighter, though not stupidly tight.

 

[rogerzilla]

Is it a freehub or a screw-on hub? The former needs cassette spacers in place of the sprockets, the latter just needs a single freewheel screwing on, plus respacing and redishing. I built a Campagnolo Record rear hub into a dishless singlespeed hub -sacrilege!

 

[Sharky]

Your chain just looks too slack. You should be able to move the chain up/down at the mid point, no more than one inch.
If you can't move the wheel back, you need to take out a couple of links to get the tension right.

Good luck

 

[Chris S]

If you can't achieve the correct chain tension by removing links then add a chain tensioner.

 

[C R]

If can't achieve the correct chain tension by removing links then add a chain tensioner.

There's a reasonable amount of travel in those dropouts, it should be possible to get the correct tension with the correct length of chain.

 

[ColinJ]

There's a reasonable amount of travel in those dropouts, it should be possible to get the correct tension with the correct length of chain.

I have done it on a second bike which I converted to singlespeed and which now lives on my turbo trainer. I think when the chain starts to lengthen I will be able to tighten it by removing a pair of links, replacing with one half link, and making a slight adjustment to the axle position in the dropouts.

 

[ChrisEyles]

Chain is way too slack, so moving the wheel back in the drop outs to add a bit of tension should help keep the chain on the desired sprocket.

You need quite a good chain line, so that the front chain ring is in the same plane as the rear sprocket - this may or may not give you the gear ratio you desire as the bike currently is. If you run the chain at too much of an angle it will be much more prone to jumping off, and will run more noisily.

I'm guessing that's a freewheel rather than a cassette?

If so you'll need to redish the wheel when you swap the multi-speed freewheel for a single speed one. While it's not exactly rocket science it's quite fiddly first time you try to do this.

If it's a cassette, it's much easier just a case of moving spacers around until you line the rear sprocket up with the front chain ring.

Good luck! Ask on here for help if you need it

 

[All uphill]

I've converted a couple of bikes from derailleur to single speed and gone the easy route by buying a complete new rear wheel and then choosing a bottom bracket that lines up the chain wheel with the sprocket.

As said above the horizontal dropouts will remove the need for a tensioner keeping the drive train nice and simple.

Welcome and good luck - post some pictures of the finished job please!

 

[Sharky]

What's the non drive side of the hub? Is it threaded? In which case just turn the wheel round and fit a single speed freewheel.

 

[PillowOnChest]

Thanks a lot for all of your replies!
I hit a busy period so it will be a while before I'll be able to put all your good advices and experiences into my own project. I will definitely post pictures and a review of the result. Again, thanks a bunch!!