noremedy

I have a giant bowery and i have decided to go with a smaller chain wheel ( i live in the blueridge mtns and 48t is a lill much for me) I was thinkn about something like a 35t but i dont know what cranks i need for a bike like this, as i have come from a bmx back ground. Could i use bmx cranks on this and if i do what do i need to as far as the bottum bracket. I guess i am clueless about this so any help would be great.

dutret

A bmx, mtb or compact road crankset would work. with 35t clearence shouldn't be an issue.
Pick a crankset then a bb to match.

BostonFixed

Just change the rear cog and/or buy a smaller chainring. Much cheaper and less hassle.

What is the current gearing on your bike now?

ryand

I don't think anything else can really be said. Those are the two options you have. Any they will both work.

BostonFixed

If you are running the stock 48x18 gearing, I'd reccomend you buy a 42 or 44 T chainring if you really want to gear down.

noremedy

would a 42 be a big differnce? and i am not sure if it will fit on the current crank cause of the crank arm has the spider looking thing that attaches to the chainwheel.

marqueemoon

42x18 should be plenty low for street gearing. It's probably a 130mm bolt circle crank and 42 tooth rings are readily available. So are 39 tooth rings but I think that's overkill. I don't see any reason to go down to 36x18. That's seriously low for the street - more like singlespeed MTB gearing.

noremedy

thanks for everyones help i will try out a 42 tooth and see if that helps.

BostonFixed

You don't need to buy a new crank- the chainring unbolts and you can bolt your new 42t ring on.

mihlbach

Let me second Bostonfixed's first suggestion. Leave the crank and chainring alone and just get a bigger cog...much cheaper and simpler to change. A smaller change in the number of teeth on the cog will result in a more dramatic gear change than changing the same number of teeth on the chainring. I would go with a cog that has maybe two more teeth than what you have now, that will lower your gearing as much as about 6 less teeth on your chainring.

If you only change the cog, rather than changing the cranks and chainring...
1. you probably won't have to add or remove links from the chain
2. you won't have to worry about messing up your chainline
3. its cheaper
4. cog thread sizes are pretty standard. Chainring bolt circle diameter is not. Thats one less thing to worry about with a cog change.
5. The whole idea of the track cog is to change it depending on the situation. Chainrings, on the other hand are not as readily swappable.
6. Big chainrings look better than small chainrings.

noremedy

so if i have a 48 X 18 setup now i should either move to a 42 X 18 and have to take out links on the chain
or if i understand the correctly you suggest adding 2 more t the cog thus meaning i would need to ask for a 20t cog. Making my setup a 48X 20?

mihlbach

If you move to a 42 tooth chain ring, you will have probably have to remove at least one link in the chain and possibly two. Dropping 6 teeth will move your axle back 3/4 of an inch. Removing one link from the chain will bring it forward 1/2".

On the other hand if you add two teeth to the cog you will move the axle forward only 1/4". Your present chain length and rear dropout will probably accomodate that. Look at the position of your axle right now..is there some room for it to move forward?

Your present gear (48/18) is 70.1 gear inches. Thats a pretty standard gear for urban fixed gear riding.
If you move to 48/20, you will be pedaling 63.1 gear inches...thats pretty low for road fixed gear.
42/18 will give you 61.3 gear inches...thats slightly lower but about that the same as 48/20.

You might also consider 48/19 - thats about 66.4 gear inches...sort of intermediate.

If you have the money to burn, buy a 19 and 20 tooth cog and swap between the 18-19-20 tooth cogs as needed. As you ride more and get stronger and develope better technique, you may find that 48/20 is too low. That all depends on how steep your hills are of course....

dabern

Not trying to add to your confusion, but I live in Asheville NC and ride these mountains on my fixed...by "mountains" I mean the 6-9% grades, not the 15-20% ones. Right now I'm on a 45x20 and it's about right for here as long as I don't try the really steep stuff...I don't know where in the BR you live, though. Generally speaking, 3 teeth on a chainring is about equal to 1 tooth on a cog...42x18 that you're talking about would be roughly equivalent to a 48x20 but with the 48x20 you'd really have no lower to go so I'd say get the 42 tooth CR and then see how it goes...if you need lower then try a 19 or 20 cog with the 42...your results may vary, of course. Anyway, good luck!

dutret

the 1=3 thing only works if the gear ratio is around 1:3(48/16 or 42/14 for example). At 42/18 you are much closer to one tooth in back being two up front.

one tooth in the back or front is approximately 1/8" of axle movement or half a chainlink difference. That will be more or less true for any reasonable gearing.(I was wrong and have changed this to keep people from getting confused.)

noremedy

I am In Roanoke virginia

noremedy

the axle is sitting almost center in the rear drop outs, I could move it up 3/4in or back a half.

mihlbach

Great...that give you several options. BTW, you can get cogs up to at least 22 teeth.

here are some examples...
https://sheldonbrown.com/harris/fixed-sprockets.html

Retem

if you get a new chainring and cog it shouldn't be more than 45 bones

mihlbach

You should think this through more carefully...its more like 1/8" per tooth. I recently went from 42/15 to 45/16. I added a total of 4 teeth and I added 1 chain link and got the exact same axle position. Adding 4 teeth = 1 link = 1/2" axle movement. Therefore, adding 1 tooth = 1/8" of axle movement. Sheldon says the same somewhere on his site. The reason it only move 1/8" per tooth change, and not 1/4" is because the chain only goes roughly around half of each sprocket. Adding 1 tooth = 1/2" greater sprocket diameter. The chain only goes around about half of that, which means there is only 1/4" more contact of the chain and sprocket. Effectively that makes your chain 1/4" shorter. The chain runs both above and below the sprockets, so shortening the chain by a total of 1/4" only moves the axle 1/8".

noremedy

Thanks for the link i ordered
i ordered the 20th phil wood
and the sugino 42t chain ring the one for the 130mm
I ll add the cog first and go from there and again thanks for all the help

dutret

Indeed you are right. It's been a while since I've had to worry about that and I got confused.

mihlbach

Good luck!

I shoulda mentioned this...but you need to know whether your drive chain is 1/8" or 3/32"...that describes the width of the chain and the thickness of the cog and chainwheel. The link I provided you was for 3/32" cogs. That width will work with either a 1/8" or 3/32" chain...so you should be fine if you ordered from the page that I linked. But just for future reference, singlespeed/fixed gear chains and cogs come in two widths. 1/8" sprockets (thicker) will only work with a 1/8" chain. 3/32" sprockets (narrower) will work with either type of chain.

Retem

just get an 1/8" chain kmc z chain is usually 6 bucks