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d2create
05-26-08, 06:36 PM
Before I added the half link my chain was very taught with maybe a quarter inch of movement if I lifted or pressed on it. Then by just adding the half link there is way too much slack... At least 2"! Never expected to get that much. Would going from a 48t ring to a 47 give me that much slack?

05-26-08, 07:27 PM
Apparently so.

jsharr
05-26-08, 07:52 PM
did the two things occur at the same time. You decreased the size of your front ring and lengthened your chain? If so, then yes, it may well could.

d2create
05-26-08, 08:25 PM
did the two things occur at the same time. You decreased the size of your front ring and lengthened your chain? If so, then yes, it may well could.

No.
So what I'm wondering is if going one tooth smaller on the front chain ring (and removing the half link) will make as drastic of a difference?

And no, this is not the IRO.

BCRider
05-26-08, 09:17 PM
Yes that sounds about right to me.

Think if it in terms of triangles. Draw a long but shallow equilateral triangle with a long flat base and two equal upper parts with a 1/4 inch of center height. Now measure the lengths of the two equal upper sides. Then add 1/4 inch to each upper side and arc them up from the ends until the inner ends meet again. You'll be amazed at the "slack" you'll see.

CaptainCool
05-26-08, 09:49 PM
If you're running SS/fixed on a bike with vertical dropouts, there's a more elegant way to find the magic gear combo for your bike.

Yes that sounds about right to me.

Think if it in terms of triangles. Draw a long but shallow equilateral triangle with a long flat base and two equal upper parts with a 1/4 inch of center height. Now measure the lengths of the two equal upper sides. Then add 1/4 inch to each upper side and arc them up from the ends until the inner ends meet again. You'll be amazed at the "slack" you'll see.
Yep. To run some numbers:

Assuming a 17" chainstay, in half is 8.5". Half of a half link is 0.25", meaning there's 8.75" of chain for 8.5" of chainstay. Pythagoras says that means about sqrt(8.75^2 - 8.5^2) = 2.1" of extra vertical slack.

d2create
05-26-08, 10:30 PM
If you're running SS/fixed on a bike with vertical dropouts, there's a more elegant way to find the magic gear combo for your bike.

Is this what you mean?
http://eehouse.org/fixin/javafmu.php

I ran the numbers and it says I need one tooth less on the big ring which is why I'm asking if that will make as big of a difference as that half link. I sure hope not.
Just trying to double-check before buying a new ring.

CaptainCool
05-27-08, 09:44 AM
Is this what you mean?
http://eehouse.org/fixin/javafmu.php

I ran the numbers and it says I need one tooth less on the big ring which is why I'm asking if that will make as big of a difference as that half link. I sure hope not.
Just trying to double-check before buying a new ring.
Yes, that's the calculator.

I think one tooth on the chainring will be about half as much change as adding or removing a half link. There will be about half a tooth difference in the amount of chain touching the chainring.