Chainline and BB Spindle Length?
 

I've been mostly lurking for a while seeing what's up in the fixed world while I dream of not coasting. Y'all have lots of arcane knowledge, and you're usually very encouraging to beginners, which I think is important, spreading the word, rather than flaming the noobs.

I think I've got almost all the parts I need either here or in the mail, but I was just looking at my (pink rattlecanned cheapo oldie with 120 spacing) frame and realized that duh, I don't have a bb (I know it's standard 68mm english though), and I have no idea what spindle length I'd need. I have a 600 double crank, and I was hoping to use the outer 53 tooth chainring with a 20 tooth Soma kog.

So pardon me if I've got dumb questions, I'm a xc mtb'er and a commuter, and this will be my first build ever.

I searched threads on this board and read Sheldon Brown's article on chainline, but I'm still not sure about a couple of things.

Do I figure the hub chainline by adding the hub shell width to the cog width? I got the formula/mavic wheels from nashbar (don't have them here yet, so I can't measure, but I guessed they were equal to Sheldon's measurement of the IRO track hub), so I think that gives me a rear chainline of 42.3mm. What about the front though? He says that a road double is 46 to the outer ring, so how do I calculate my spindle length to get a 42 or 43 mm chainline to the outside? Do I have to put the big ring on the inside? This looks kind of ugly to me, but I see it's pretty common on fgg for conversions, which this is, so I'll do whatever. I screwed this up before putting a road triple on my commuter mtb even with a gigantic bb spindle (122 on a un72 I think? I don't really know, I did what my lbs told me and cried later), and I don't want a second frame with big gouges out of the chainstay.

Sorry I can't measure any of this stuff, I've only got the frame, bars, seatpost and crank here now. Brakes, levers, bar tape, stem, wheels and cog on the way. Oops, that reminds me that I don't have pedals. I guess the atacs get cannibalized until the trails dry up, or is that ridiculous for a newcomer in an urban area (Montreal)? I just realized I don't have a chain either. Or crank bolts. Jeez, does it ever end?

This will also be my first bike that I've cared about aesthetics on - mmm, pink and black. It'll be probably 20 pounds (64cm and old) too, which is like 8 pounds lighter than any bike I've ever been on, so I'm psyched.

Thanks in advance.

Sheldon Brown's numbers for adding hub width from center to shoulder to width from edge of cog to center of teeth are pretty accurate. 42-43mm chainline sounds typical too.
If you move your crankarm/spider inward to get a 42-43mm chainline with the outside position, your crankarm is going to be REALLY close to your chainstay. Probably in a bad way. Then you gotta get your left crankarm over too... sounds like a big pain. I would just use the inside position, you don't have to futz around as much, just bolt on the chainring and go. If it REALLY bothers you then look into BMX cranks or real track cranks for that smooth look.
As to the "Jeez, does it ever end?" No, no it doesn't. :D

Depends on what your chainstays are like, I have cleared the stays with the crankarm by less than a cm in most cases. Use a Cheapo UN-53 BB (I don't like the plastic cup on one side, but it works fine) they have them in a wide range of spindle widths. If you are getting a track wheelset you shoud have your rear end all set, depending on the shape of you chainstays you might have trouble with a 53 tooth ring (it could hit the chainstay), I have a track frame as well and I doubt I could fit even a 51 and my chainline is deadnuts on...why not go with something like a 48X16 or maybe 48X15, less chain, less weight and more likely to fit. Get cm ruler and go by sheldon's measuring guidlines and you should be square, don't forget the sigle stack chainring bolts. Hope I helped.

Theres a page on Sheldon's site which will tell you what bb spindle length you should have to partner your 600 crankset. You'll need the part number stamped on the inside of the crank arm.

Be careful though that may be the spindle width for a road double that may not give you the chainline you need.

You are adapting road parts to a track frame. Key Word : ADAPTING- you must find a way to nail that chainline if you care to have a smooth running drivetrain. So, you must find the BB that best accomodates your goal. You could use that BB for the 600's but you will be stuck using the inside chainring position, considering you want to use a large ring up front I can almost guarantee it won't fit (chainring will hit chainstay).

Thanks for all your suggestions.

Just to clarify, I don't have a track frame, it's an I think 70s road frame with long horizontal dropouts. I'd be converting my road frame and crank to fixed.

I have no idea what kind of shapes chainstays come in on road or track bikes besides 'normal', but they look pretty narrow, so I won't have fat tires or fenders, but they make me think (without pulling out a tape measure or ruler or anything) that I can move the crank in a get the outside 53 on there.

I'm going 53x20 for several reasons - gives me a gear in the mid seventies (I'm fairly strong but I'm 235 pounds too), I already have a 53 tooth chainring, and this town kind of sucks for getting parts in my experience, and more teeth will mean less wear on my drivetrain. I do actually have a 48 tooth chainring on my commuter bike that's getting singlespeeded to the middle ring, so I might be able to experiment with chainrings too.

So if Sheldon tells me I need a 113 for 43.5mm chainline on a 600 double, assuming my ring clears, does that mean I can just find say a 111mm spindle bb (assuming I can find that?) Except looking on the harris cyclery page I see they jump from 109 to 113. And I'm not ponying up for a Phil bb :)

Hmmm. I'll see how close I can get to the frame and eyeball it, I'm beginning to see this is an exact science, sort of.

120mm spacing is standard track drop out spacing, given that you are getting a track wheel set right? You will only need to contend with the front alignment. Some chainstays have somewhat of an hourglass shape (usually newer frames, vintage will most likely be straight maybe with a crimp or 2 or none). When I first set up my fix that I got off Ebay it came mostly complete with Suntour Superbe Pro Track cranks and Shimano UN-71 BB 68X115 I discovered that this BB was not right for my crankset (way off)...I then embarked on a mission find the right one, Sheldon's info pointed me towards a Campy 111 squaretaper symetrical BB being that I too didn't want to dump tons of dough on campy or phil finally I happened upon a Miche track BB (super-cheap-dissposable) and it had the right taper for my cranks thanks to the advice of John at a well known track shop in Miami. I learned a lot from this experience. The nice thing about the Miche is that the cups do not have a flange that sits flush up against BB shell so you can adjust the BB position slightly inside the BB shell, pretty cool. After this experience I moved on to doing some conversions with old road bikes, the first was for my friend so he could get out with me. His old bike had some old cast Sugino GT cranks and the matching BB. The inside ring was in the right spot for the 42-43mm chain line, but I was bummed about how cludgy it would look with just inner ring...turns out that the 115x68 UN-71 i had lying around was the perfect fit and it was symetrical..go figure perfect SS/fixed chain line. Best way to figure out which one you need would be to have the right BB for your crankset measure from the center of seat tube to the center of the outer ring, subtract 42mm or so from that measurement and you should come up with a pretty close idea of what the difference in the BB you nedd should be. Confused? lets say your spindle is 126mm and the distance from the seat tube to the center of the outer ring is 56mm you would need a BB with a 112mm dimension to get the right chain line..easy. I just made up those measurements for the sake of example. Also keep in mind that a a millimeter or so of difference is not the end of the world the sound of your chain might be a little bit noisier...and more than a couple a mm off and you run the risk of throwing the chain especially with a 3/32" link. Hope I did not just confuse the hell out of you.

With the recommended BB splindle length(113mm) for 600 cranks you would end up with a 46 mm chainline on your outboard ring. To get to where you need to be you will need a 109 mm BB. 109 might be hard to find in the sealed variety(outside of expensive track BB's) but 110 is pretty common and should do the trick for you.

You dah man...good call!

better to undershoot the chainline if need be cuase there's always spacers you can put between the driveside cup and the frame. give you that adjustment for the perfect chainline.

the 3mm difference is removed entirely from the drive-side? really?

I think old 600 cranks get a good chainline with a 107mm BB. Even think Sheldon Brown recommends the same.

Actually, the driveside difference between a sealed shimano 113mm and 110mm will be 3mm on the driveside. But, I really wasn't completely correct.

The best answer here if we are dealing with shimano sealed BB's would be 107 OR 110. You might say that this sounds strange but the only difference between the two is the non driveside length. Whereas, the 113 differs from the two on the driveside by 3mm, as I said before. This is strange but, Shimano does strange things sometimes.

After rethinking this a little bit(read: no longer brutally hungover) the best choice in a Shimano sealed bb would be as techone said, the 107. This will eliminate the ugly 3mm gap that will appear on the non driveside. This is going to give you a front chainline of 43(if we believe what Shimano tells us about the exact chainline the crank BB combo will give us, the best idea would be to measure but we can't do that in this case)

The next step is to determine what your rear chainline is going to be. This relies on the type of cog you are using and the hub that you have. The 42mm track chainline is more of a heuristic than a reality. The hub/cog combination in the back will really dictate your chainline. Once you figure that out you can decide if any spacers will be needed(BB or axle). If you nail the 43 with your hub/cog combo then you are done.

I say shoot for the 43 with your combo, so wait for your wheels to come in and measure 'em to the best of your ability and go from there.

May I barge in on this thread to ask another, possibly related question? I'm also building my first fix and have picked up an Il Pompino frame which has 135mm rear spacing. Would I be better off going with a 135mm rear hub, or getting a 130mm hub and using spacers to fill out the gap, (or pulling the rear triange in a bit) which would be more compatible with other road frames, or even with the Jamie Roy, which I've also got my eye on. Thanks for your help.

Just a minute ago I installed old (sth like 82-84) Shimano 600 cranks with a UN52 107mm BB and outer ring chainline seems to be just about 42,5mm!

Quote:

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Originally Posted by jinx_removing

Actually, the driveside difference between a sealed shimano 113mm and 110mm will be 3mm on the driveside. But, I really wasn't completely correct.

The best answer here if we are dealing with shimano sealed BB's would be 107 OR 110. You might say that this sounds strange but the only difference between the two is the non driveside length. Whereas, the 113 differs from the two on the driveside by 3mm, as I said before. This is strange but, Shimano does strange things sometimes.

After rethinking this a little bit(read: no longer brutally hungover) the best choice in a Shimano sealed bb would be as techone said, the 107. This will eliminate the ugly 3mm gap that will appear on the non driveside. This is going to give you a front chainline of 43(if we believe what Shimano tells us about the exact chainline the crank BB combo will give us, the best idea would be to measure but we can't do that in this case)

The next step is to determine what your rear chainline is going to be. This relies on the type of cog you are using and the hub that you have. The 42mm track chainline is more of a heuristic than a reality. The hub/cog combination in the back will really dictate your chainline. Once you figure that out you can decide if any spacers will be needed(BB or axle). If you nail the 43 with your hub/cog combo then you are done.

I say shoot for the 43 with your combo, so wait for your wheels to come in and measure 'em to the best of your ability and go from there.

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mmmguhhh...head hurts. I actually had no idea about the driveside vs non-driveside gaps and road vs mtn bbs, but now googling the problem, I see this is something I could have looked up I I'd've known that it was something I could look up. I don't think I'm going to be able to find a 107 in this town, but I'll call around, you never know.

My Soma cog and Formula hub ought to give me a 42.3mm chainline in the back, I hope. According to Sheldon's page anyway.

How about another crazy question about chains? I went with 3/32 for my cog to keep chain problems to a min (finding them in town I mean), but if I'm going to order a bb from somewhere, I can order chains too. I'm actually also converting a mtb to SS with a conversion kit so I'll need two new chains:

Is it crazy/pointless/stupid to go with a 1/8 chain on a 3/32 drivetrain? I know lots on this board go with a 1/8 cog and chain and 3/32 chainring, but I decided to go with Sheldon Brown's advice that it doesn't matter *and* that I thought I had a new 7 speed chain laying around. Now I realize it's used, so ... now what? The thicker chain will look cooler, but... problems? I remember new 7speed chains and new cheap cassettes getting the chain pretty snagged on the unused cassette teeth, and, um, I have no idea. This cog will have bigger teeth than a ramped cassette cog? Or something?

This will leave only tires to go.

Oh no.

And a seat binder bolt.

Dang! :o