Bottom Bracket sizing question
 

I am building a new bike because my old one got hit by a car with me on it. And hopefully I'll have some money to play with. I am considering buying a basso coral frame and all ultegra components. My question is does the bottom bracket measurement of either 68 or 70 deal with the frame or the crankset. Or, more bluntly, do I need the BB with Italian sizing of 70 to fit my frame or does that number correspond to something else. Thanks.

That measurement is the shell width of the frame and is usually independent of cranks. 68mm and 73mm are typically English threaded while 70mm is typically Italian threaded.

http://www.nashbar.com/tech/images/shellwidth.jpg

You will also need to get a BB with proper spindle sizing. This is dependent on the types of cranks you want to use. Triple cranksets typically require longer spindles. And while there are some typically used sizes (108mm for doubles, 118mm for triples), they are not set in stone and recommendations vary from one crank manufacturer to another. Also, you may want to go with slightly shorter or longer spindle lengths than what's recommended in order to tune your chain line for smoother shifting. This would be dependent on your frame geometry.

http://www.nashbar.com/tech/images/spindlelength.jpg

The diameter of the bottom bracket shell is biggest give away concerning the need for an English or Italian BB -- an English BB will pretty much fall straight through an Italian BB shell because the difference is about 1.2mm.
Also, the Italian shell has a right-hand thread on the drive side, but it's sometimes tricky to tell just by looking at it.

And, as Khuon said, once you determine the "nationality" of your BB, you must get the right width axle for your cranks and the desired chain-line.

Great photos, Khuon!

The recommended spindle length from shimano or campy gives the correct chainline.And neither gives you the choice of fiddling with different spindle lengths in their current offerings. 'Frame Geometry' has nothing to do with it either, except in the case of MTB BB where a longer spindle is recommended for frames with a largr diameter seattube,but that is not really 'geometry'.

I"m glad you pointed this out. On another tread the guy is breaking Front D cables tryig to get rid of the chain noise. And guess what. His shop put in a new BB that "is just a bit wider but should be fine". Even if he maxes out the High screw. It will never reach that Bit wider.

khuon
Great Info
Well Done!!

That is not exactly true. Longer or shorter spindles can be acceptable they don't cause other problems. There is usually latitude in the limit adjustmets to handle a range. One just has to check it out to be sure.

I can't claim credit for them. Those are off the Nashbar website.

I've heard of quite a few people using slightly longer or shorter spindle lengths to tune their chainlines due to extremely short or long chainstays combined with running specific gear combos. Campy and Shimano can recommend all they want but in the real world, some amount of tinkering seems to always happen to get certain things worked out.

Point being,with ocatlink you have no choices in spindle lengths, so it isn't optional. Campy only offers specific length/crank,so to get anything else you have to look elsewhere for a campy compatible taper.There is no point to monkeying with chainline wih respect to gear ratios,unless someone is always using the small and large cogs rather than the whole range.In that case they probably ought to be looking at gearing changes.

Please let me clarify, you have to know what you're doing when you change the width of the BB.

On a Custom bike yes you may have play to get the right one to get the chain line correct the first time you in stall a group. Once you have the alignment your not going to switch to a narrower or a wider one after you have gone to all the work of getting it right are you?

If you have a stock bike that had a BB that came from the factory and it fit and worked putting in a wider one might not be the best idea. If it isn't broken don't fix it.

The guy in another thread said that his shop replaced the factory BB with a wider one and now he is having problem. Depending on the Front D’s cage it might not physically be able to reach.

You just have to know what your doing. And remember that just cause a change worked on one bike doesn’t mean it will work on every bike.

Cheers

I don't presume to know what the original poster was going to use exactly (yes, they said Ultegra but that can mean a variety of things). He/she might not even be using a Shimano or Campy BB and crank combination. I thus was trying to point out things that should be taken into consideration.

There is just no basis for that either. Custom is not unique in that respect. I'll also say it again. With current groups, you have no choice as to spindle length for a given crankset. Take a look at what's offered. You do not do any fiddling around. Install the recommended BB for the crank, and the chainline is right. There is no black art involve here with either custom or production bikes.

Yeah, and it just makes the water unnecessarily muddy. And it doesn't matter if they aren't using shimano/campy. Every crank manufacturer has a recommeded spindle length for a particular crank,that gives correct chainline.And, the poster only asked a question about shell width and threading.

There are varying factours that neither you nor I can assume. Shimano states that the chainline should be 43.5mm but they also assume some things. For instance, what if the poster was building a track bike with extremely short chainstays and a large ring that had to be position a little further out because it couldn't otherwise clear the chainstay?

Well, now you are grasping.Shimano offers track cranks and BB.With a 120 dropout spacing on a track frame,I doubt that chainstay clearance is a problem,and suspect fruther that framebulders take things like that into consideration,rather than leaving it to the buyer to hopefull be able to sort out, after having shelled out their loot.

I'm not grasping. I'm telling you that I don't like to assume.

I avoid assumptions as well as not muddying the water unnecessarily. And that chainline stuff in this instance was just that:Information overload.

I merely suggested that if the person has chainline problems due to frame geometry then they should look at a different size spindle length than what's recommended. How is that information overload?

I think it's simply not an issue.You are creating a problem that is for the most part non existant. And again, how many times do I have to say: what are the options with current cranksets? The only gripe with current setups is with short chainstays and sometime chain rub on on the big ring when using the small ring and smaller cogs. The solution other than avoiding the small cogs is a thinner chain , a 1 or 2mm BB spacer or chainring spacers. Depending on the crankset, you have no spindle length options.

O.k., guys stop trying to "one-up" each other. The question got answered and you're both right! There!

L8R

I can find an FSA 113mm ISIS BB and mate it to cranks designed for 108mm ISIS splines such as say a TruVativ Elita Double in order to shift my rings out a little if I happen to be building a bike where my inner ring was contacting my chainstay when using the standard 108mm spindle length.

If the spec for the elita double say use a 108 it isn't a likely senario to begin with.Besides, the poster said he/she was using Ultegra......Also the mod said cut it out...... I'm good wit that.

I'm just building a plain road bike, not a track bike, and will be using ultegra cranksets and BB's and everything. So it sounds like I can just get a BB that fits my frame and then everything should be good. Thanks for all your help.