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Old 09-21-08, 06:24 PM   #1
daveed 
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Looking for a proper chainline (fixed gear)

Hello,
Can anyone tell me if I'll have a problem achieving a proper chainline using a 113mm spindle on mid-70s Fuji Allegro with 126mm rear spacing?

My rear wheel is set up with a Formula track hub and a DA 1/8-inch cog (126mm w/spacers). The chainring is a 42t on a vintage SR double.

A 107mm and a 110mm (Shimano) BB were not long enough; the crank banged into the stays. I guess I'll have to give the 113 a go but thought I'd inquire beforehand in the event an expert was available.
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Old 09-21-08, 06:34 PM   #2
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If you spaced the hub by just adding 3mm to each side keeping the hub centered. I would just flip the BB axle you have so the long side goes to the non-drive side of the bike. This should be pretty close, although you may have to use the inner chainring mounting position.

I usually just close the triangle to 120mm, then a Formula F/F usually lines up dead nuts with a road double axle flipped, using the outside ring position.

If you flip the axle and still have chainring to chainstay clearence issues, try running the hub at 120mm. You actually do not even have to cold-set the frame, as you will just pull it closed when tightening the axle nuts. But I prefer to cold-set then check the alignment and tweak as needed.
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Old 09-22-08, 05:41 AM   #3
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If you spaced the hub by just adding 3mm to each side keeping the hub centered. I would just flip the BB axle you have so the long side goes to the non-drive side of the bike. This should be pretty close, although you may have to use the inner chainring mounting position.

I usually just close the triangle to 120mm, then a Formula F/F usually lines up dead nuts with a road double axle flipped, using the outside ring position.

If you flip the axle and still have chainring to chainstay clearence issues, try running the hub at 120mm. You actually do not even have to cold-set the frame, as you will just pull it closed when tightening the axle nuts. But I prefer to cold-set then check the alignment and tweak as needed.
Otis, many thanks for the great advice, which would not have occured to me. I'll coldset tonight.
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Old 09-22-08, 06:02 AM   #4
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Rear spacing, and cold setting in fact, will not alter the chainline.

Chainline is a two-variable problem. Generally, in a road conversation the name of the game is to bring the chain ring in as tight as possible, and then bring the cog out as far as necessary.

Without knowing what crankset you have (which is a huge variable), I might suggest the following:

-flip the cog around on your hub so that the shoulder faces in. This buys you a couple of mm's.
-put the ring on the inside of the spider. Again, a couple of mm's.

Still not straight?

-put some spacers in-between the ring and the spider. Might get you 1 or 2.

Still?

-you either have to get a tighter/track crank with corresponding spindle or else redish/respace the rear hub. I hate to do this to a track hub since now it will not flip/flop, so I consider it the last resort.

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Old 09-22-08, 06:17 AM   #5
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measure your chainline front and rear to see where you are at.

http://www.sheldonbrown.com/gloss_ch.html#chainline
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Old 09-22-08, 07:05 AM   #6
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Your hub requires a 42mm chainline. Measure the chainline with a BB you have, do the math and buy a BB with the correct length spindle
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Old 09-22-08, 07:31 AM   #7
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And do be prepared for the fact that it is very hard to get a road crank/bb to come close to a 42mm chainline.

A lot of people think that the easiest way to get a fixed gear bike is to convert use track wheels on a road bike. Track wheels often mean getting a track crank. Or else redishing/respacing a brand new track wheel. It just seems wrong to do that.

The much maligned "suicide hub" rear wheel has more going for it than some would suggest.

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Old 09-22-08, 05:11 PM   #8
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Dirtdrop and igewa:

First, thanks for the suggestions. They're much appreciated. As for which crank, well, it's an SR, 170.

I believed the Fuji road bike conversion was a no-brainer because I built up my current fixie -- a '77 Peugeot -- sans problems. It was my first road bike conversion (I've converted three ATB frames with an ENO hub) and it tricked me into thinking all I had to was switch components and voila (or whatever the Japanese word is) I'd have a better fitting, lighter bike -- and a proper chainline.

+1 on the suicide hub; I used one for a time on an old mtn bike to no ill effect.
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Old 09-22-08, 09:09 PM   #9
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+1 on the suicide hub; I used one for a time on an old mtn bike to no ill effect.
I've never had a problem with mine, either, in many many years of riding. But leave the brakes on.
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Old 09-22-08, 09:52 PM   #10
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Road cranks have lands on the inside (usually) to seat the inner ring. If you want to convert a road crank to be more like a track crank, which has no lands, then you need courage and a deft touch with a file. That will allow you to mount the ring on the outside, with a shorter spindle, and get to the 42 mm chainline that seems to be standard. Rear dropout spacing has little to do with it, really; but if your chainstays aren't indented in the crank area, that might prevent getting a chainline that narrow.

As noted by another respondent, you can mount the chainring on the inside, but that probably makes the ring closer to 41 mm than 42. Adding a 1 mm shim under the fixed cup will move it to 42, with the same spindle you were using for road.
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Old 09-23-08, 06:33 AM   #11
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Rear dropout spacing has little to do with it, really
It has absolutely nothing to do with it. Chainline is measured from the centerline. How wide the stays are is irrelevent.

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Old 09-23-08, 05:16 PM   #12
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Quote:
Originally Posted by Charles Wahl View Post
Road cranks have lands on the inside (usually) to seat the inner ring. If you want to convert a road crank to be more like a track crank, which has no lands, then you need courage and a deft touch with a file. That will allow you to mount the ring on the outside, with a shorter spindle, and get to the 42 mm chainline that seems to be standard. Rear dropout spacing has little to do with it, really; but if your chainstays aren't indented in the crank area, that might prevent getting a chainline that narrow.

As noted by another respondent, you can mount the chainring on the inside, but that probably makes the ring closer to 41 mm than 42. Adding a 1 mm shim under the fixed cup will move it to 42, with the same spindle you were using for road.
Maybe you just have to pick the right parts. My Carlton has a 35mm chainline. The T.A. road crank is unmodified except for the removal of the inner ring and shortening of the bolts. The chainstay is not crimped. The 52t ring clears by no more than 2mm. The small bcd of the crank means that there is clearance for the lands, but not much. The dished 3 speed cog is installed with the convex side out. The bottom bracket is a 115mm Miche Primato track type that allows for some adjustment of the chainline.

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Old 09-23-08, 09:49 PM   #13
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It has absolutely nothing to do with it. Chainline is measured from the centerline. How wide the stays are is irrelevent.
Well, if the stays splay wider, then they might be very slightly further off-center at the point where crank interference might occur (assuming they're not bent). So I'm gonna stick with "little to do with it."
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Old 09-24-08, 10:52 AM   #14
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Well, if the stays splay wider, then they might be very slightly further off-center at the point where crank interference might occur (assuming they're not bent). So I'm gonna stick with "little to do with it."
I'm going to stick with my guns on this one cowboy! Chainline is the distance from center. Adding spacers outside of the hubs will not change how far the rear cog is away from the centerline. And neither will bringing in the stays affect how far the cog is from the centerline.

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