Crude single speed conversion
 

Winder and gears were not cooperating with my winter beater so I made a crude single speed by ditching the derailleurs and shortening the chain and putting it around the 14 tooth ring on the rear freewheel and the middle 38 tooth ring in the front. I took it for a test ride and the gear is higher than I prefer (I made a mistake and ended up with a chain too short to use on anything but the 14 tooth rear) but it works. Before I start using this to go to work I was wondering if there are any known issues (safety or otherwise) or things to be aware of when doing this type of crude conversion.

i don't see how it should be an issue, really no different than a factory made single speed, right? cool idea and you saved a few dollars.

Being made fun of by the guy who left his old rear derailleur on as a chain tensioner**********

Peeps been doing what you just did for years and years. If you use your old rear derailleur, all you need to do is adjust the stops to keep it in line with whichever cog you choose. It even gives you the option of "shifting" with screwdriver......

John

The main problem being that at certain times the chain will grab the next largest cog and proceed to jam up the whole system. I have done this before with limited success and also broken a chain or two. It works but not without problems in my experience.

Well I just went for a ride and 800 metres into it I heard a clank and saw that the rear wheel was out of alignment and rubbing on the left chainstay where it meets the seat tube. When I have time I'll have to check it out. I'm still not sure what happened. The chain is still in position.

http://www.bikeforums.net/showthread.php?t=283467

thread about my ghetto single speed built last april, still going strong. Never did pull the freewheel.

I've been riding a bike like that for years with no problems. Get the chainline straight and you're golden.

I've been riding a bike like that for years with no problems (and no derailleur adjustments:D). Get the chainline straight and you're golden.

You have to make sure the QR or axle nuts are done up really tight. It's not a chain or cog problem. I think it's one of the reasons why track bikes come with special track nuts that allow you to reef down without damaging the dropouts -- the force of the chain on the rear cog is very strong when getting going from a standing start, and will pull the wheel to the left side.

It seems like your chainlines are out... that maybe the chainrings need moving outward to the right with a BB spacer or a new BB spindle length.

Seems like that is what happened. If memory serves it was while moving off from a standing start.

The imperative to remember is track nuts come on track bikes....track bikes are fixed. The torque on a fixed gear is much heavier when you push to stop the pedal rotation.

On a single speed the forces are no higher than on a bike with many gears. With horizontal dropouts you run the risk of torquing the wheel out of place on a SS or a geared bike.

But the diagnosis seems correct. I would try tightening the QR. I've torqued plenty of wheels sideways with geared setups, too. With vertical dropouts this is prevented.

Thanks for the input. I tried again to go for a ride. I really reefed on the nuts and took off. Things were ok until I rode onto a curb. Clunk! Got off and tightened till my hand hurt. Was ok until riding along and . . . clunk. This time I got an automatic upshift (which surprised me as the chain seemed too short to go up a cog). Bike still rides but I feel the drivetrain slipping. I double checked later and the wheel is off centre as well. I might have to chalk this one up to experience. I was looking to replace the bike in March/April. I might have to do it now instead.

you can just remove the rear derailer if you have horizontal dropouts to tension the chain.

If the cassette in question is a Shimano Hytrout a derailer to keep it precisely lined up. The chain would ride up and down that cassette at random, and when it moved onto a larger cog, it would sometimes pull the wheel out of alignment.
I tried to solve the problem by taking the cassette apart and just using a single hyperglide cog with spacers I salvaged off the cassette and a hardware store PVC, cut pipe, spacer. But no matter how much I tried keeping the chain tight, the chain derailed very often.
When I switched to a Surleycog made for use with hyperglide cassettes it worked beautifully - no more thrown chains. I read that other manufacturers have similar cogs that should work fine.

That first line should have read "If the cassette in question is a Shimano Hyperglide, you probably need a deraileur to keep it precisely lined up".

The frame has a horizontal dropout. The freewheel in old and rusted out so not much to be done with it. Thanks for the advice though. I have not given up on building an SS, just have to reassess the resources at hand.