Singlespeed ratio problem

simonj1234

I'm trying to fix up a single speed rig but I'm having a few issues.

I bought a DMR 16 tooth conversion kit with a Surly tensioner with the intention of driving it with a 32 tooth chainring.

I've set everything up as it should be but the chain keeps skipping over the rear cog and is completely unusable. To make sure it was the rear cog that was the issue I tried a 12 tooth cog off a 9 speed cassette and it seems to work fine.

My question is, if I use the 12 tooth rear cog with a 22 tooth chainring will it be exactly the same as using a 32 tooth chainring with a 16 tooth rear cog. My calculations seem to think so but are there likely to be any issues with a 22-12 setup?

Thanks, Simon.

demmerson

Your gear ratio won't be quite the same, it will be slightly lower. The easiest way to work it out is to divide one by the other so 32/16 = 2 and 22/12 = 1.833. The chain will probably wear a bit more quickly with the smaller cogs.

Try a new chain?

simonj1234

Sorry, I actually meant 22-11 as opposed to 22-12. Would that be similar?

I've tried 3 chains already, a nine speed MTB, a seven speed MTB and a BMX/Singlespeed chain. (All brand new).

I'm not too worried about quicker chain wear as it's a second bike anyway. Basically as long as 22-11 would give me a sensible-ish gear with minimal disadvanteges over a more conventional 32 tooth chainring then I'm happy.

david 142

No big issues with 22/12, but a potential one with using a sprocket from a cassette!
In cassette sprockets the teeth are cut down and have ramps etc designed to make the chain dismount easily. Not fun if you're giving it some welly!
The sprocket from the kit should have full depth teeth. IMO its worth finding the cause of the problem.
I'd suggest 3 things to double check:
Chain tension - not too slack.
Chainline - use straight edge or taught string rather than eying it up.
Wheel alignment - is slightly skew?
It might be worth checking your frame alignment before starting. I discovered that mine was 6mm to one side. The wheel looked okay against the chain stays but the sprocket was nowhere near where it was expected to be.

2wheelzgood

I'm sure you've checked this, but the DMR cog isn't a 1/8 size is it?

demmerson

2wheelzgood wrote:

I'm sure you've checked this, but the DMR cog isn't a 1/8 size is it?

I wondered about that and checked the DMR web site but it doesn't specify. http://www.dmrbikes.com/?Section=produc ... mid=CDSSCK

2wheelzgood

you should be able to notice is by looking at it, or lining it up which one of your cogs for a casstte, as they will be 3/32.
HTH

But I think most of these kits are 3/32. INfact I'm pretty sure the DMR Simple chain tensioner only takes a 3/32 chain.

Are you using a worn chain with it?

I've been told that new cogs with a worn chain is a bad idea and they will slip.

another jacko

Another thing to check is whether you need to use the chain tensioner to pull up or push down on the chain to keep it tensioned. The Surly chain tensioner should have come with 2 alternative springs. One pushes the tensioner down, with the roller inside the chain to tension it, the other pulls the tensioner up with the chain running over the top of the roller. Which one works best is trial and error and depends on the sizes of the sprockets, the ratio of the sprockets, the length of the chainstays and whether you are taking up the slack of half a link or one and half links. Basically it is trial and error. I had to change mine over to go from a 42 -18 to 42 -16 and then back again when I went up again to 44 -16. When it is not right the chain skips as if you've got a badly worn sprocket.

Hope this helps.

nicklouse

simonj1234

You will not find any 11T cogs that fit on a cassette body. the smallest is 12T.

another jacko

He will, easily. Most MTB cassettes have an 11T smallest.

But, as David 124 said, they are not the best option. Deep tooth sprockets are best for this application and it should be possible to make 32:16 work.

nicklouse

another jacko wrote:

He will, easily. Most MTB cassettes have an 11T smallest.

but as that is the last cog it does not go all the way onto the body. Ok get the file out and remove the stops and it will fit and then add a speacer to the flat side and then modify the DMR spacers... and do you want to use a shaped geared cog on a SS set up?

stickman

Maybe you could fit a front derailleur to keep the chain alignment you want, you wouldn't need a cable and shifter, just use the adjustment screws to line it up.

FlatEssexSociety

quick add to this.
I'm changing my rear cog from 16t to 14t and need to fit a new chain too (this is on the MTB). Turns out bigger lad, heavy leg, old chain, etc, etc, etc

I'll need a 3/32 chain, but having never changed a chain before, do the pins come with, do I buy them separate or what? (I'll have to reduce the chain length)

david 142

I would expect to find the parts necessary to rejoin a new chain packed with it. For Shimano that would be a single use pin - press in and snap off. For most others it would be some sort of clip together link. Some of these are also single use IIRC.
I would recommend ditching the lot! When you buy your chain buy the appropriate Sram Powerlink at the same time. Proven reliable and reusable, so you can readily remove and replace your chain if desired. Very convenient when cleaning in cold weather