cyrano138

If I'm replacing the whole assembly, cups, cones, axle, bearings, lock rings, etc., does it matter if it's 3s, 3h, or whatever?

It seems like as long as I match the shell width and the threading and the spindle type (jis vs iso?) I'll be fine, right? I realize different spindle lengths will give me different chain lines, but that's what I'm trying to do. I'm doing a fixed gear conversion and I don't want to have to mess with re-dishing the wheel.

Thanks for any help!

Iride01 

The codes probably matter depending on what you want. Sheldon has a table that shows some of the differences between some spindles.

https://www.sheldonbrown.com/bbsize.html

As for re-dishing the wheel, I wouldn't think that your spindle will affect that. Your dishing is determined by the centerline of your bike and what ever you put on the drive side of the rear hub and the dropout spacing.

So the rear wheel choices drive the choices you need to make on the BB, not the other way. Of course the spindle length will determine in you have the correct chainline with whatever crankset you use.

cyrano138

My thought was that, since I'm already buying a crankset and I don't know how to re-dish a wheel (or have a dish tool), I can just buy a BB with the spindle length that will give me the chain-line required by the rear wheel with the track cog on it.

Iride01 

Yep, that is what you need to do. If you get the wrong bb and crankset combo, then you have to change either the bb or crankset to get the chainline required to your rear cogs.

You don't change the rear to match the front.


Did you see in Sheldon's table how the spindle number and letter affect how far the spindle sticks out from the drive side and non-drive side? That's what you have to worry about. Along with the fact that square tapers in my experience required too much trial and error to get things where you wanted. However some might look at them allowing you to more easily be able to get to where you wanted. But they must have lots of spares laying around to try for free.

cyrano138

I figured, since I have the original BB which is almost certainly too long on the drive side for the chain-line I need, I can measure the chain-line as is and figure out how much shorter I need the drive side to be, then buy accordingly? I'll measure for chainstay clearance as is also, so if I end up getting an overall shorter bb I won't get caught unaware on either side by clearance issues.

I just wanted to make sure in my original post that purchasing a different letter bb wouldn't somehow cause issues with the shell itself. I know that sounds like a dumb question but I just didn't want to screw it up.

Iride01 

You have the right idea about it. Just don't willy nilly buy one without knowing how much sticks out to the left and right side of the bike.

The letters and numbers make a difference. So find the specs if they don't readily have them for you. While you might can live with too much sticking out the left side, it'll look funny to some of us. And too short will be and issue if the crank rubs the shell.

I got frustrated with my square tapers trying to find the perfect crank that sat at the proper chainline. I switched to a 2 piece crank and bb for my BSA threaded shell and never looked back or regretted the change. But if you are trying to keep a somewhat vintage bike somewhat period looking, then you'll have to play with it some and might have to make several swaps to get everything correct.

Surprised none have come out yet to give you a better answer than I possibly can. I admit I'm a little biased against square tapers.

cyrano138

I guess I like they're cheap, serviceable, and at least used to be easy to get.

All good advice though, thank you

cyrano138

Three problems here: I already have to get new cranks (the old ones were steel and weigh about 500 lbs), and I don't have a table (I do my work on the driveway or on the bike while it's strapped to the rack on the back of my truck) or any cd cases.

In all seriousness, I do want to do more with wheels, maybe eventually even build a set, but I've played around with truing them enough now to know that, even if something is straightforward in theory, in practice it can be very difficulty to do even small jobs.

If I didn't already have to replace the cranks i'd give it a shot, but I'd rather ruin a wheel I don't need for a build.

Rolla

Yes, you'll be fine. I've replaced a couple of BBs to achieve the chainline dictated by the hub and cog. Not being a stickler for vintage spec, I went with a cartridge-style, but the same measurement and clearance principles apply. All told, it's maybe a 15-minute job; re-dishing and truing a wheel would take me a lot longer.

cyrano138

If I can't find one that works I'll go with a sealed cartridge one. I'm not that particular, but I like that the original style is serviceable.

Rolla

Agreed, but honestly, the only service I've ever performed on a sealed BB was to replace it every three or four years, whether it needed it or not.

hokiefyd 

Yes, one of the nice attributes of square taper bottom brackets is you can customize a drivetrain exactly like you're doing. I may have overlooked it, and I apologize if I have, but do you have an existing bottom bracket spindle in the bike now? If so, you what the current chain line is and you can adjust from there to get your desired chain line. Remember that, assuming a symmetrical spindle, your chain ring will move outboard by half of the length increase. That is, if you get a spindle that's 6mm longer than your current one, half of that will be on that non-drive side and half of that will be on the drive side. So if you need to move your chain ring over 8mm, then you need a 16mm longer spindle (again, assuming a symmetrical layout).

As others have noted, wheel dish is (almost certainly) not a factor here. Unless you're working on a bike with very fat tires and your chain line is going to be small and you need to move the tire and rim to the left for chain clearance...dish won't be an issue. You can re-dish the rim to the left or to the right, but that's not going to change the spacing of your rear sprocket in relation to the frame. In other words, dish won't affect your desired chain line at all. This is not at all to discourage you from learning more about how to do that stuff, but it shouldn't be the long pole with this particular project.

cyrano138

Thanks, I had a pretty good idea what to do but now I have a clearer idea. My understanding is that re-dishing comes into play when the front of the drive train is a given, and axle spacers are used to align the rear cog with the front chainring. Following that, the re-dishing re-centers the wheel relative to the frame.

hokiefyd 

I see what you're saying. Yes, if you are changing the lateral spacing of the hub within the frame with moving axle spacers around, then you may need to adjust the dish. If you're just changing the spacing of the sprocket with spacers on the hub, and the hub spoke flange itself is not moving left or right within the frame, then the dish wouldn't change.

Road Fan

If you're already buying a crankset. it's probably simplest to just buy the BB that is recommended for the crankset. Is that not possible? If you can just get a Shimano cartridge of the current common grade with the recommended spindle length, why would that not be satisfactory? What complicates it?

Road Fan

That work could take longer, but maybe not. It's mainly more exacting - you have to do enough of the correct adustment to every spoke, and it might not be the same adjustment for all the spokes. And you have to have the technique not to round off the spoke nipples with the spoke wrench.

Rolla

I've built, trued, and dished a lot of wheels and replaced a lot of bottom brackets. Unless the BB threads are frozen, wheel work always takes me a lot longer.

cpach

This is true, but sometimes people will respace hubs to adjust chainline, which requires a redish, which is what I assume OP is referring to.