nome.king

This has probably been covered here before, but I can't find anything on it.

Is there any reason not to run a 12 tooth cog and a 34 tooth front chainring, which gives a ratio of 2.833, almost equal to the ratio of a 15/43 or 16/45 drive?

Thanks

drac_vamp

small looking?

Kiecker

Chain wrap and engagement. More teeth, more teeth engaged.
Availability of 12t fixed cogs.

goldener

https://www.surlybikes.com/spew3.html

read the macro vs. micro drive part. [ignore the part about offroad mtbing and chain tensioners]

Kiecker

Why ignore? This forum is for SS/fix gears....nothing explicting saying road not mtn. The original posted also made no mention between the two and left it open. Another reason why I clairified about 12 tooth fixed cogs and not ss cogs.

Proud owner and rider of both fixed and SS mtn bikes.

gtboy

Suntour is the only company that made 12t cogs, and you need special lockrings for them. It's probably just easier to run like, 13/36 or 37, or some other equivalent.

goldener

nobody would ride a 2.833:1 ratio off road. unless their definition of off road was flat pavement.

Kiecker

Fire roads.

goldener

are never flat enough to justify a 2.833:1 ratio. I'd also say that a 2.833:1 ratio is even too high for the street, even for a flat city.

gtboy

I run a 3:1 on the street. I live in Los Angeles, which is NOT a flat city. I generally spin 110/120+. Gearing is a matter of personal fitness, not absolutes.

Speaking of personal fitness, Kiecker: Are you Cat 2? I want to take a spin at ADT, but I haven't taken their classes, and I'm not Cat 2. Did you take the classes? Do you think they'll let me on during the open training without them? I've been riding at Encino for a bit now.

Maybe this is better said in PM.

xowl

what city do you live in? i cant think of too many people who ride lower than 46x15 which is what i ride on one of my frames. on my pursuit i run 48x15 but im thinking of switching it to 43x14 which is bearly higher than 46x15. i am only considering it cause i have the extra chainrings lying around. although for some reason the higher ratio seems no different. maybe it's the geometry.

that surly blog doesn't make that great of a pitch for not going micro. although i don't know if 43x13 is quite micro. i could understand if you weighed a lot, but for a smaller person it seems alright.

nome.king

Thanks everyone. The reason I ask is because I have a NOS Suntour 12 tooth cog that came with a box of random parts I bought off eBay. I wasn't aware it required a special lockring, however. The project is a city/commuting bike with 26" wheels and narrowish tires. I usually ride 14/42 on my 700c bikes, so the gearing is actually a quite a bit lower than I'm used to, but its a utility bike and I may carry large loads occasionally. If the cog will wear fast and skip than it isn't at all appropriate for this task. It will probably wind up on my little German folder.

531phile 

Hey, Xowl, how's Chris doin' over at Cycle A Cyclery? I haven't seen that guy in a while. Post your track bike for all the world to see.

xowl

haven't talked to him for a while. last time it was to ask how to get a seized post. (note: don't let excitement of recieving a hand built frame get in the way of assembling a bike properly.) got that taken care of tho. once i get my new wheel set, i'll put up some pics.

useless127

i dont know if anyone said this yet, but micro gearing puts more torque on your chain, chainwheel, and cog. i also ride bmx and there is this whole micro gear craze going on right now. i've seen 23/9 gearings, and not on a flatland bike either. kids are getting crazy, but i digress. the lower gear ratio you go, the more torque and (eventually) wear will be put on your drive train, in turn, making it deteriorate faster.

humancongereel

i saw that a shop once. guy was working on this bmx with tiny, tiny gears. it really threw me for a loop. no idea what the ratio, or gear inches, or gain ratio or anything was, though. it just looked like spinny mcspin-spin.

treechunk

I run a 45x17 in Chicago on my fixed gear. There's a stop light almost every half mile here, it really doesn't make sense to have a monster gear if you spend all your time speeding up and slowing down. Plus, if you run a lower gear, you'll accellerate faster than the cars as well as any higher-geared folks. Seriously, it works.

As far as micro drives, what Surly says there is true. You are going to wear your shti out quite a bit faster, and it is more likely to skip. The more surface area that your chain is engaging the less likely you are to have the chain slip. My tallbike doesn't do well in the small cogs 'cuz the chain doesn't wrap as much as it would on a regular drivetrain.

I've got some stuff coming together for a 26" fixed gear, and I know for a fact that the frame doesn't take a chain ring larger than like a 34 tooth or so. I'm gonna be running a 12t cog to make my gearing workable for street use. I'd rather not, but the stays are shaped for super-low off road gearings, not street use, so I gotta.

mascher

Sheldon sez:

https://www.sheldonbrown.com/chain-life.html

highlyselassie

It's a bit like standing on a slightly frozen lake, you don't weigh any more than if you was lying down, but all your weight(torque when relating the analogy back to bikes) is concentrated on a significantly smaller surface area.

Personally I would reccomend exactly the opposite, i.e going for a 20+ tooth sprocket, if it's feasible.

1. Your torque is spread evenly over many more teeth, increasing sprocket life.
2. It's also spread over a larger part of the chain, increasing chain life.

LóFarkas

^^^And it looks like a bigger ratio as well

highlyselassie

Which is by far the most important thing when around other ss/fixers

huhenio

81 inches for city riding is not all that crazy ... but trying to go fast up the hill will be useless

76 ish will be better

Aeroplane

Sell that Suntour cog to some track freak and buy yourself a complete drivetrain with the money you make.

gally99

i ran 50/14 all over oakland and SF...
there's plenty of people running similar...
your high horse looks ill...

xowl

i guess the higher ratio comes from racing all the time. i do know one guy who races with a relatively small gear. when we do races in the park he kills it on the final incline. but he also spins a lot. i have another friend who used to live in SF and he still rides a low gearing. i borrowed his bike once and didn't like the gearing. but for city riding, i just blow through the lights most of the time. and if i can't make it, that's what trackstands are for- so you can take off from a standing start faster.

i understand the surly thing, but i think weight might be an issue. if you weigh like 150lbs, i think that might help on wear and tear. a small high ratio is probably not a good idea for someone weighing over 200lbs. besides, im going from 48x15 to 43x14 which is a bit lower anyways. i wish i could do 43x13, but thats a track ratio and i can't even race this bike cause it's a pursuit!