Singlespeed & Fixed Gear - Ate pavement on my new SS build

So (I thought) I finished my SS build this week. I took it out for a quick spin around the block before I left for work. Started cranking on it pretty hard and the chain came off the ring and I ate s***:cry: like never before. All scraped up, hit my head on the asphalt, etc. (No sympathy from wife).

Anyway, I used a Bontrager road crank and just removed the large ring so I'm running the 39 tooth. I've got a 13 tooth cog in the back from an old road cassette I took apart. I'm using what I believe to be a 1/8" chain from my spare parts box. The tension seems decent, but I'll try to put in a half link as soon as I can find one (frame has vertical dropout).

Now I'm asking your suggestions....is this a chain tension issue? Or is there a problem running a chain ring designed for shifting? (i.e. the teeth aren't tall enough?) Any guidance is appreciated.

im not really sure about the chainring designed for shifting, but some of my friends tell me that their chains have occasionally popped off when their tension was a bit too loose, so it very well could be a tension issue

If you're running it SS but not fixed, you might be better off installing a chain tensioner to help with that. Glad you're OK, sounds pretty cruddy for a first trip out.

Make sure your drivetrain is all the same size... Thats my only guess.

That 13 tooth cog is only going to engage 6.5 teeth and with the shorter teeth it will not hold a chain as well as a proper ss cog...I have used 14 tooth cogs off of cassettes in the past and they really are not the way to go if you are going to hammer things.

Add a little chain slack or a rear wheel that isn't well secured and the recipe for disaster starts looking pretty complete.

I run normal 3/32 chain rings in most of my fg bikes with no issues but my rear cogs are all ss / fg specific, and my chain lines and tensions are perfect.

Check your chain line and chain tension, make sure the alignment is dead on and consider running a larger chain ring / cog combination for your preferred gearing.

Most important of course is that you are okay.

I use a Shimano Ultegra 42 chain ring meant for shifting and over 2 years have never had a problem with it coming off, get a tensioner and you will be fine.

Whoops... I just saw the vertical dropout bit.

Forget the half link... you need a chain tensioner.

Yesterday on my way home from work I decided to skip stop up to a light instead of braking, and my chain hopped right off. Turns out my "Ehhh, it'll be fine until I get home" tension wasn't quite enough. Not only was I glad I had a brake, but I learned to always get that chain tensioned up, because next time I might not be so lucky as to just keep rolling.

Yeah, get a tensioner. You'll be glad you did.

i had my chain fall off due to tension once and it ended up costing me because it caused the rear wheel to lock and i skidded right through a tire

Thanks for sharing your experience. There's literally no one in my town to ask about SS/FG. I'm going to improvise a tensioner tomorrow out of an old rear derailleur while I shop for something a that looks a little cleaner. I may also tinker with putting on the 53 tooth ring and a larger cog; you know, just because I can.

Thanks everyone.

i had my chain fall off due to tension once and it ended up costing me because it caused the rear wheel to lock and i skidded right through a tire

This happened to a friend of mine because he decided to loosen his chain way up for some reason, except it was lucky as hell because he was bombing a hill with no brakes at the time.

All you need is a tensioner to prevent the chain from flying off.

Thanks for sharing your experience. There's literally no one in my town to ask about SS/FG. I'm going to improvise a tensioner tomorrow out of an old rear derailleur while I shop for something a that looks a little cleaner. I may also tinker with putting on the 53 tooth ring and a larger cog; you know, just because I can.

Thanks everyone.

Just use the old derailer as is... there is no better tensioner out there than this.

Threw on an old rear derailleur this afternoon; problem solved. I prefer the look without a tensioner, but what can you do? The bike has to have one in order to be rideable. Thanks for all the help!

bummer dude hope you recover quick....i too a couple spills yesterday too haha

i dont think anyone mentioned it, but is your chainline bad?

I bet, its the teeth on the rear cog , esp. if its from a cassete ... its designed, to have the chain climb off of it easy . ( the teeth are shorter & have little ramps in the side and some of the teeth are twisted a bit. )

A ss/kit tensioner might band-aid your isue, but it wont fix its cause ...

Kinda like balancing a bent ( car ) wheel .. you can put weights on it & it will "balance-out" on the fantsy computerized spin balancer ... but I bet it will still shake and vibrate the car like crazy. ( since it doesent straithen the wheel. )

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i dont think anyone mentioned it, but is your chainline bad?

Chain line is good.

If you wanted to be really sure, get a 3/32" singlespeed chain (specifically singlespeed - less lateral flex), a large (maybe 17t) BMX cog, and a 48t singlespeed ring. You're probably just fine with a derailer-as-tensioner though.