singlespeed conversion question
 

my search didn't turn anything up--i don't know if i didn't search right or what, but i'll have to ask it here.

i'm in the process right now converting the lady friend's geared bike to a single speed (and i'm going to post pics when i post ones of my new track ride...the paint job sucks on the soon-to-be SS and we'll work on that, but the lugs are sweet).

paranthetical run-ons aside, i'm just about done with it, when a question occurred to me...how much of an issue is chainline for a single speed? it won't be fixed. well, maybe eventually--she's expressed interest in that. but right now it'll only be a quickie ss conversion, leaving the original gears on until either of us can afford a bmx cog. i figure that if, with derailers, you could run the outside chainring and inside cog, you could do that with this. it's not "good" either way, but won't ruin or throw the chain.

i'm NOT going to do that, more of a 53/14 or 15 maybe, but the 15 jerks the chainline off straight a little more than i'm comfortable doing without knowing if i'll **** up her bike and maybe her by doing that.

hmmm...i just looked at sheldon's gear calculator, and while she was orignally wanting 53/11, i conviced her to let me move it up a bit in back. it's still about 97 inches at the least there, so i may do 40/13 or 40/11 (since backpedalling won't be an issue). those will still be slightly off, and the question still stands: is that bad on ss? this whole time i've been reading up on fixed gear and don't know **** about ss.

I don't see a problem with it, considering geared bikes almost never have a straight chainline. If I understand you correctly.

that's my line of thinking. plus sheldon has nothing to say on the subject at all.

i guess i can always **** with the chain some more if there's a problem.

Is it possible to remove the cassette, and replace it with a single cog and spacers? I've seen it done on MTBs.

So... it's got a screw-on cassette? If the chainline is a little slanty, it'll be okay. If it makes noise from the chain being stressed, you might want to play with the spacing a bit (different BB, moving the chainring from the inside to the outside of the spider, etc) ... but for the most part, straight-ish is fine.
If it's got a free hub, get some spacers and put the gear where it's best for the chainline. You can get spacers out of old cassettes, or buy one of those conversion kits - but used ones are cheap and effective.

bmx cogs are under 20 bucks. how broke are you?

yeah, eventually a bmx cog and spacers will come into play...but right now i'm just leaving the cassette on and shortening the chain.

okay...so i guess since i can mess around with the chain length some more, i can lay around with and just gauge it by noise...i know a couple of candidates for gear combinations would cause more than others, but the 4 big ones are straight-ish.

i do kind of want to flip the chainrings, but i haven't got a crank puller. the cranks are old suginos that look like i could maybe get them off without one, though. that'd be interesting...as far as i know, they don't make cranks like that.

Kind of off the main topic of conversation, and I don't know what the terrain is like out there, but I'm currently riding a 52x19 fixie, and the gearing is a good ratio. It's about 74 gear inches. 53x14 sounds a bit difficult. Granted it's not fixed, so you are coasting, but hills may be a bit of a *****.

yeah, with coasting, i'm not thinking it'll be all that hard. i'll probably end up messing around with it...but, you know...she asked for 53/11 initially, so i'm just moving it down a few inches. there's some hilly terrain here, but it's mostly long distances with a slight incline the whole way. the only huge hill has a commuter train going up it, i'm sure she'll want to take that for a while.

you don't need a crank puller to flip the chainrings. just undo the chainring bolts with a 5mm allen and bolt it onto the other side of the spider. old sugino road double? i've got a soft spot for em.

Good chainline on a singlespeed is still very important, for the same reason its important on a fixed gear. Its that big dangly derailleur thingy in back that helps make geared bikes work without perfect chainline, because it ensures that the chain is fed onto the rear cog nice and straight, even if the cog isn't in line with the chainring. Remove the rear derailleur, fixed or free, and bad chainline will cause problems.

I do not know. I am more comfortable riding the hills with higher gear on my fix than on my road bike.

53x11 and 53x14 are both HUGE for street riding.

I run 48x17 (74.2 gear inches) fixed in semi-hilly Seattle and that is plenty. I know Portland is flatter than Seattle, but unless your lady friend has legs of steel (in which case my hat is off to both of you), it seems like 40x14 is the best of your available options. 40x14 is 75.1 gear inches with 700x23s according to Sheldon.

Like the poster above said you can move the 40 ring to the outside if you want pretty easliy.

yeah, this bike has 17x1/14"s (marueemoon)....

as far as the rest of y'alls' comments, i've decided to go with a 49/17 match up...which is, what, um.....the high 80s, as far as inches go, right? it's not far from my 48/17 gear on my track bike, and i think she'll like it. chainline is almost prefectly straight. rolls smoothly. but the high 80s on a freewheeled bike ought to be okay. we'll work out pariticulars when we get up cash to put on a real cog and redish the wheel...hell, she's thought about a fixie before, and i won't discourage her. at all.

oh, but it's good to know about flipping the chainring. if i ever need to do that....now i'll know just how.

What the hell? Either you mistyped the size of the wheels (17x1/4) or you are WAY off on your gear-inch calculations.

As far as chainline, it won't matter too much with a SS if you keep the cassette on, the worst thing that can happen is the chain slips onto a harder gear and you get off and put it on again.

When you do get to the point where you remove the cassette and just have one cog, then it is VERY important, especially if you use one of the cogs from the cassette. They are designed to throw the chain, and they will if the chainline isn't right.

But I really think you should either check your math or your typing.

hee hee, yeah, it's 27. oops.

thanks aeroplane, that's sort of what i was thinking--that chainline might be important later, but not now. i was sort of concerned with the side to side flex of the chain, but i guess i was just being cautious.

This thread didn't make too much sense, but:

Use the middle ring [if triple] or small ring [if double], and pick a cog that lines up reasonably well.

Oh, and BMX cogs are <$5.

Small gears are the ****! Try starting with the middle ring, and a cog halfway down the cluster in back. That'll both give you a decent chainline, and a decent gear.

Do this:

[and don't forget to oil your chain!]

I'm so confused. So you ride the exact same gear ratio as me fixed (48x17 for about 74 gear inches) and you want your lady friend to have a gear ratio in the high 80's? Unless she is much stronger than you (which I'm not ruling out), it seems like a bad idea. Secondly, if you meant that her bike has 27x1/4 wheels 49x17 is about 78 gear inches, which seems a bit more reasonable than the high 80's. I wouldn't personally ride a gear that tall, but maybe I'm a wimp.

If you haven't done so already, try plugging some numbers into this.

I guess the bottom line is you have some cogs and some chainrings to experiment with and that's what you and she should do, while keeping the chainline as straight as you can. Numbers don't mean much in the end. I know plenty of people who push gears I would never choose, but they are happy.

I am positive that she cannot push those 53x11 on hills ... or perhaps she is a freak of nature with disregard of spinning.

hmmm, i just thought a higher gear would make sense, because of not spinning every time going down a hill. as it is, we're running about the same gears...but she'd originally asked me for something a little taller.

sorry this thread didn't make more sense last night. when i work on bikes, i drink. and that sometimes makes the questions i have kind of weird.