BROCK SAMPSON

to singlespeed my bike without a chain tensioner? I have an 8 speed rear cassete and a 2 speed front. I want to convert it to a singlespeed so I'm keeping the 32 tooth front sprocket and I'm planning to get a 16 tooth for the rear.

barba

You need to provide more information. If your bike has horizontal dropouts the answer is yes. If the bike has vertical dropouts the answer is still yes, but you will need to find a "magic gear" or use one of these.

_dhan_

I'm assuming that you have vertical dropouts or you wouldn't even ask this question. it is possible if you find that "magic gear" where your chain tension is ok. This means that you might not be lucky enough to have 32-16 like you wish. I had a magic gear going for a while, but now I think my chain is wearing out a bit, so I tossed a tensioner on there.

here's the relevant bit from good ole sheldonbrown:
"Adding or subtracting a link in the chain will move the axle 1/2". Changing either sprocket size by one tooth is the equivalent of moving the axle 1/8" (4 mm)."
https://sheldonbrown.com/singlespeed.html

so... if your axle is in a fixed position, you have to play around with adding/removing links or increasing/decreasing the number of teeth

BROCK SAMPSON

https://www.norco.com/2007bikes/Mount...036723e36734e8
Well thats the 07 model of my bike, it should have similar or the same geomatry as my frame if that helps at all.

pyze-guy

Or save $155 and use a halflink. Allows for 1/4" of adjustment. Makes a world of difference with vertical dropouts. No need for the enohub for s/s, would be a waste of money. S/S doesn't need a super tight chain like fixed. To make it work well you need non-ramped chainrings and cogs. No matter how good the chainline and tension are, ramped parts will throw the chain.

BROCK SAMPSON

I know I seem like a complete 'noob' asking this but what are ramped chainrings? I think I know what they are but I'm not sure.

_dhan_

chainrings and cogs made for use with derailleurs have ramps and pins and short teeth for the purpose of improving the movement of the chain OFF the chainring and onto the next. when you only have one chainring and one cog, this is a very undersirable feature.

BROCK SAMPSON

Okey doke, thanks, thats what I thought it was.

Rowan

Pardon? I don't get this idea that ramped cogs and rings will "throw" a chain. The ramps and piins only come into play when the chain is shifted against them by a derailleur from the adjacent chainring when shifting up. They are "dormant" at all other times. If the scenario you and pyze put up is true, then chains would be thrown off cogs and rings on multi-geared bikes. Even with tension on a SS chain, they don't have any influence on a chain's path.

Oh, and Brock, maybe look at just using the freehub you've got with presumably the 16T already there, and get some extra spacers to replace the cogs you take off. That way you don't have to worry about a new hub, you can get the chainline you want with the spacers, and you might find the "magic gear" with a cog either side of the 16T.

pyze-guy

Even with a staight chainline with perfect tension they will throw. Had it happen with my last s/s conversion enough times under different circumstances i.e. cranking hard to start, up hills, over bumps. Bought a non ramped cog and problem solved.

BROCK SAMPSON

I kinda disagree with you on that, my chain skips to other gears all the time and thats one of the reasons I want to go ss, I guess it's all up to riding styles, I guess a more aggressive riding style like mine would throw the chain more, but if your riding placidly, I don't think the chain would move much at all like you said.

Yeah that was the plan, to keep the hub I have now and get a spacer kit with a new cog (16t). Would I be able to pull that off without a tensioner?

Rowan

If your chain jumps to other gears, you've got derailleur adjustment problems and similar. Riding style shouldn't come into it.

I agree that the sideplates of the chain would likely encounter the pins if the teeth on the chainring are worn. But I've just closley inspected what happens on the FG I am building, and with a Shimano 42T ring with a seven-speed chain, the sideplates come close, but don't touch the pins. I don't disagree that a non-ramped and pinned ring would be ideal, but then I'm a guy who built up another FG with a Biopace ring and *never* had a chain drop, even at 120-plus rpm, and plenty of climbing... and people said that couldn't be done.

pyze-guy

Go here to find out.

seely

Ah yep, so obviously its a given if it happened to you. Makes sense. Especially since I'm sure no one in the history of biking has used a ramped ring on an SS with any amount of success. Good point.

BROCK SAMPSON

Are you beeing sarcastic? I honestly can't tell.

skingry

If you're going single speed you can adapt your derailleur to be a chain tensioner.

pyze-guy

Gee I'm sorry, I thought the whole concept of this forum was to present ideas and suggestions, usually based on our own experieince to help answer others questions. I assumed that because it happened to me (a 99% exclusively fixed and s/s rider and I do know something about cassette hub conversions having done 4 now) and I know of others in the fixed s/s forum who have said the same, that it was a good suggestion. Next time I'll check with you first, to make sure you agree oh almighty. Is that alright?

So what's your experience with ramped cogs on s/s conversions? What can you offer to this thread?

seely

I know of at least a dozen conversions with ramped rings (including three or four of my own) that are fine. What bothers me is that there are many documented conversions with ramped rings floating around, and many websites that would suggest you just remove two rings and use your middle ring for a conversion. If this didn't work, no one would be advocating it. What bothered me about your post is that you say a ramped chain "will not work". C'mon. Generalized (and unsubtantiated) statements like that are dangerous and unfounded. Had you said "over the past five years I've built 5 SS bikes and I know a few others who have found ramped rings to pose a problem", that would have been fine. But, to declare a ramped ring the source of all that is evil is a bit of a stretch, especially when I know, and have had "personal experience" with many, many conversions with ramped rings.

As someone else said, the ramps are on the inside of the chainring and only affect shifting. If you chain was coming off, something else was going on. Either the ring wasn't straight, some teeth were bent, it was worn out, you were using a BMX chain on a 8/9spd ring, etc.

Grand Bois

Rowan and seely are correct. Ramps and pins on the side of the chainring have absolutely no effect on a single speed setup.

Avoid using a chain tensioner if you can. You can find the "magic gear" by using trial and error with the cogs on your cassette. It took me about a minute to find the magic gear for my Trek.

barba

I agree that ramped chain rings should not cause the chain to derail. If that was the case we would constantly be skipping gears on multi-speed bikes. I suspect that pyze-guy's problem was elsewhere (chain line, etc.). I used a ramped shimano ring for a year and never had the chain skip.

Grand Bois

How could the ramps have any effect at all when the chain never touches them? I use unramped rings on my singlespeeds, but only because it looks better not to have ramps and pins that don't need to be there.

pyze-guy

I don't recall saying anything about a ramped chain and I said to make it work well. Don't make up quotes about things I never said. And how is this a dangerous suggestion?

I thought my statement about my, and others, conversions was just that. "I do know something about cassette hub conversions having done 4 now) and I know of others in the fixed s/s forum who have said the same, that it was a good suggestion." I like the melodrama about all that is evil. Winner move.

Ramped cogs, not just chainring.

Why would I make up stories about thrown chains? To impress people? Jeez, if you disagree fine, just don't be such a princess.

pyze-guy

Ramped cogs, I never should have said chainring. As well I should have said can throw a chain, not will.

waterrockets 

Not necessarily true. 1/4" of slack is plenty of room to throw a chain on a bump. There is a chance that for a given bike and gear combo, that no wheel movement is necessary, but I wouldn't ride around with 1/4" of slack.

I have an Eno, and they only cost $129. I tried to make it work w/out the hub for a while (I'm very frugal), but kept dumping the chain. The Eno is a wonderful hub, and I'll be building my RB-1's new wheel with one to build my hill-climb bike...