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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 05-21-08, 03:08 PM   #1
jlakser49
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a work in progress

Here are a couple of pictures of the bike I am currently working on.
I got this bike for free on long island. I was able to strip the gears and make it a single speed for no money.

I haven't replaced the crank or the gear cogs...the bike runs well but now it is time for the fixed gear conversion.

I went to my lbs and was able to get a aluminum 27 inch wheel with a fixed cog. (it was ordered I am waiting for it to come in).

After that I will take off the back brake and keep the front one...possibly change the lever and caliper.
add some straps to my pedals and I should be ready to go for now.

eventually I would like to replace the crank because i realize that it isn't the most ideal set up for a fixed gear bike, but for now I would like to get some millage out of this crank before I decide to replace.

hopefully you guys can answer some of my questions with the given pictures. so here goes:

1. With this crank and the new rear wheel with a fixed cog...should i have any issues with my chain line?

2. Right now i have the chain around the inner chain ring on the crank, witch one should i use for the fixed gear set up?

3. When I do replace the crank what kind of bb will I need and what kind of crank do you think I should use?..I would like to keep it below 100 dollars so any suggestions would be appreciated. (I realize I prob need 165mm cranks)

lets hear your thoughts...
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Old 05-21-08, 03:27 PM   #2
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Measure your chainline.The new wheel will be 42mm,so if you're within 40-45mm you'll be fine.As far as the chainring, the inner will probably be better(again chainline).If you like the gear you're running now and if the chainline is good just get a cog with the same toothcount.I'm guessing your chainring is about 40T and the cog you're on is 15 or so.That would be a 72 inch gear wich is not bad for fixed.What bb you'll need depends on what crank you'll buy.
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Old 05-21-08, 06:52 PM   #3
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thanks i just measured the chain line and it looks like i am going to be all set. i think your pretty much spot on as far as my gearing is concerned right now. i think the chain-ring is 40t and i know the cog is 15. will i be alright if i have a 16t cog on my new wheel?

thanks for all the help
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Old 05-21-08, 07:22 PM   #4
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You'll be fine with the 16.
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Old 05-21-08, 08:14 PM   #5
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gear inch-wise it's fine at 67.5 (recommended ~mid 60-low 70s depending on terrain). However, if you plan on skidding a lot, you might want to look into another cog/chainring as your current one will only give you two patches, If not, then you're perfectly fine.
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Old 05-21-08, 08:36 PM   #6
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are you talking about the cog in the picture or the cog that is going to be on my new wheel. what do you mean my current cog/chainring will only give me two patches?
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Old 05-21-08, 08:43 PM   #7
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when u skid, there will only be to spots on ur tire that will be skidded on, therefore those spots will wear down much quicker, the ideal skid cog size is a 17 from wat ive heard since it will usually give u the most even wear on ur tire (ie. most skid patchs)
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Old 05-21-08, 08:47 PM   #8
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He's refering to the 16t cog and skidpatches.Skidpatches are the spots where the tire wears when skidding.Different chainring/cog combinations result in different numbers of skidpatches.This is only a issue if you plan on skidding alot and long.
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Old 05-21-08, 08:56 PM   #9
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Quote:
Originally Posted by dervish View Post
when u skid, there will only be to spots on ur tire that will be skidded on, therefore those spots will wear down much quicker, the ideal skid cog size is a 17 from wat ive heard since it will usually give u the most even wear on ur tire (ie. most skid patchs)
17 is popular because you'll get 17 patches with any combo except with a 51(1 patch)and it's not too big.A19t will give 19 patches but that might knock the gearinches down too much unless it's paired with a relatively large ring.16 will give 16 patches in certain combos and so on.
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Old 05-22-08, 10:59 AM   #10
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i guess that makes sense considering your feet are always gonna be in a similar position when you stop.
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Old 05-23-08, 08:08 AM   #11
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if i have a 16t cog how many how big should a new crank be if i want to have the proper gear inches, and also create more spots where the tire will wear during a skid, but thats not as important because i don't know how much i am going to be skidding
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Old 05-23-08, 11:41 AM   #12
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well, if you're not planning on skidding, the you can just worry about your gear ratio/gear inch

to calculate your gear ratio, take your chainring tooth count and divide it by your cog tooth count. (what you have now = 40/16 = [2.5]2.5[/b])

to get your gear inch, multiply that number by the diameter of your tire. (27 is used as a nominal value that is close enough for most needs) (so: 2.5 x 27 = 67.5---which is good and fits in the general recommendation of mid to high 60s to low 70s)


finally, if you want to get your skid patch count, take your chainring over your cog count again and reduce that improper fraction to its lowest terms and the denominator is your patch count.

--there is also a little sidenote if you skid with your other foot forward (both feet) which could double your patch count and that is if the denominator(or numerator--I forget which) is odd; this isn't really something you need to worry about too much though.

to put that as an example, of your 40/16 = 10/4 = 5/2 and the two is your patch count.

if you really are concerned about your patch count, the general consensus as I see it is to get a prime number of teeth on your chainring and not worry about it.

Again, if you plan on using your brakes, then don't worry about all this and just go with it.

good luck
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