[mjlarocco]

I am planning on building up a Soma Rush frame and I've got some chainline questions. This has probably been asked before. So the frame has a 120 mm rear hub spacing w/ a 68 mm bottom bracket.

How do I know what length bottom bracket spindle I should use to get the proper chainline?
Are hubs universal so there is a standard chainline or is every hub different?
When I am buying hubs (going for a fixed/free hub) what do I need to consider when it comes to the chainline?
How does the crank/chainring effect chainline?

I a 100% newbie when it comes to a "real" single speed or fixed gear. I had an old road bike that was converted to a SS but its not the same thing...

Thanks for any help you can give.

 

[Jesse D Smith]

This article may answer a few of your question more clearly than I could.
http://sheldonbrown.com/bbsize.html#chainline

 

[Dave Hickey]

What crankset do you plan on using? Spindle length will be determined by which crankset

 

[innergel]

Standard bb length for a straight chainline on a converted road double is 107. Come to think of it my dedicated track bike (120 rear, 68 bb) with a Miche track crank is a 107 as well.

 

[FatTireFred]

Standard bb length for a straight chainline on a converted road double is 107. Come to think of it my dedicated track bike (120 rear, 68 bb) with a Miche track crank is a 107 as well.

how can you know that without knowing what crank the dude will be using?

 

[Richard]

how can you know that without knowing what crank the dude will be using?

Ditto. The Shimano 600 crank on my fixed used a 112mm spindle and using the inner ring position I'm spot on the chainline with a 120mm Formula fixed hub.

A 107 would put the chainring into the stay.

 

[mjlarocco]

So when I pick out the crank ... I'm considering a Sugino messenger. I looked it up and a 103mm spindle length is recommended. My question is what is the mathematic formula (or formula) to come to that conclusion?

 

[roadfix]

The amount of crank spider offset is different from brand to brand. A manufacturer will recommend the correct spindle length for their particular crank to yield a 42mm chain line, for instance.

 

[innergel]

how can you know that without knowing what crank the dude will be using?

I can't know for sure. But I've built 4 fixies/ss bikes and they've all used a 107 bb.

I've got Shimano 600 converted road doubles, mounted on the inside, on two bikes and they both use 107 bb's. I don't know how it works out but it always seems to come down to a 107. At least for me.

Go with what Sugino says, which looks like 103.

 

[Richard]

So when I pick out the crank ... I'm considering a Sugino messenger. I looked it up and a 103mm spindle length is recommended. My question is what is the mathematic formula (or formula) to come to that conclusion?

The Sugino Messenger (same as the RD 48) specifies a 103mm. But I tried (because I had one) an NOS Shimano UN-72 at 107. With either the fixed or free side, the chainline is very good (if not perfect) and the drivetrain is quiet as a tomb.

On my Fuso, with the old Shimano 600 and a 112mm (what that crank originally called for) Stronglight BB, I had to put a 2mm spacer on the drive side so that the 42 chainring, mounted in the inner position, would barely clear the chainstay.

Eyeballing it, the chainline is about 2mm (surprise!) off. But with a DuraAce cog and the KMC stainless chain, it too is very quiet.

 

[FatTireFred]

The Sugino Messenger (same as the RD 48) specifies a 103mm. But I tried (because I had one) an NOS Shimano UN-72 at 107. With either the fixed or free side, the chainline is very good (if not perfect) and the drivetrain is quiet as a tomb.

On my Fuso, with the old Shimano 600 and a 112mm (what that crank originally called for) Stronglight BB, I had to put a 2mm spacer on the drive side so that the 42 chainring, mounted in the inner position, would barely clear the chainstay.

Eyeballing it, the chainline is about 2mm (surprise!) off. But with a DuraAce cog and the KMC stainless chain, it too is very quiet.

dang, that's close... why not ditch the spacer and run the ring on the outside position? or is the chainline error +2mm on the crank?

 

[DIRT BOY]

Standard bb length for a straight chainline on a converted road double is 107. Come to think of it my dedicated track bike (120 rear, 68 bb) with a Miche track crank is a 107 as well.

My Tomasso with a Powerspline Truvativ/SRAM Turo cranks was 108mm.

Now using Turvativ Turo cranks with a square taper 113mm BB and all seemms good.

 

[Richard]

dang, that's close... why not ditch the spacer and run the ring on the outside position? or is the chainline error +2mm on the crank?

I tried that and the chainline was decidedly better with the spacer and the ring inside. And a miss is as good as a mile.

 

[steel515]

does anyone know why track bikes have different size of chain/cogs than road double? 1/8 vs 3/32. http://www.thebikebiz.com/Cogs_Lockrings_s/122.htm

 

[roadfix]

does anyone know why track bikes have different size of chain/cogs than road double?

Can you be more specific? Are you talking about the number of teeth on the chainring? If so, they are available in most any chainring sizes so you're able to fine tune it to the exact gear ratio that suits you on the track.

 

[Richard]

Eating crow.

dang, that's close... why not ditch the spacer and run the ring on the outside position? or is the chainline error +2mm on the crank?

Well, I had nothing else to do the other day so I thought I'd fool around with this.

My "determination" that the inner chainring position would be better was based upon measuring from the centerline to the ring. During the build, I put the bb in and just "slid" the crank minus chainrings onto the spindle. It just seemed that the outer position was too far out - like 3-4 mm.

So, sorta needing to do some basic maintenance anyway, I pulled the crank and bb, ditched the spacers, moved the ring to the outside, and torqued it all back together.

The chainring is about 2-3mm farther out and the chainline is far from "perfect." But I decided to ride it and see.

Guess what? With the better quality KMC chain and the DuraAce cog it just sings right along. 65 miles the last two days and I'm convinced it works just fine. Plus having the chainring on the outside just looks much better.:thumbsup:

 

[FatTireFred]

do you have 2-3mm of spacers you can move on the hub, driveside to nondrive? then recenter the rim and... perfect chainline. apparently there are days where you have nothing else to do

 

[Richard]

do you have 2-3mm of spacers you can move on the hub, driveside to nondrive? then recenter the rim and... perfect chainline. apparently there are days where you have nothing else to do

If it were noisy, I'd do that. But it runs as quietly as it did before. 3/32" chainrings and cogs with a 1/8" chain seem to be more "forgiving" of a less than perfect chainline.

 

[jmlapoint]

Chainline is not difficult at all if you use a freehub for your rear wheel.
Put the front chainring on the inside of your crank.
Use hub Spacers and a single cog on the rear.
I use Chris King Aluminum Cog and Chris King Spacers.
A start would be 4 inside Spacers, the Cog, then 3 spacers and your freehub locking ring.
Lay a ruler on the chainring and see if the Cog lines up with your Chainring.
If it does, go for it.
If it doesn't, change the spacers until it is close to centered. It needs to be close, but not necessarily perfect to avoid chain drop.

 

[jmlapoint]

My setup is the same as Richard.
Shimano Crank with Sugino Ring (42) on the inside like he shows in his picture.
Shimano Rear Freehub with Chris King aluminum Cog (47).
Chris King Aluminum Spacers: 4 medial to Cog, and 3 outside the cog.
Works great with no chain drops.
No 'Tension Device" for smooth clean chain and chainline as per Sheldon Brown at Harris Cyclery.