Triple Bottom Bracket Question
 

I am shopping for a triple bottom bracket and I am seeing 2 sizes, 111mm and 115mm. Is there an advantage to one over the other in terms of smooth shifting functionality. What comes to mind (and I realize we are talking about very small distances here) is perhaps from an alignment standpoint that one might be better than the other in terms of ring to ring movement on the front and also the reduction of cross chaining. I would probably be using this with a Racing T crankset. Perhaps this is a stupid question, but I remember being told that the only stupid question is the one not asked. Thanks for any helpful comments.

111mm is for bikes with a 28.6mm seat tube and the 115mm is for bikes with larger seat tubes.

I have a 28.6 seat tube so I could use either one. So going back to my original question, is there any advantage in terms of positioning/alignment (less cross chaining, ease of shifting on the front, etc.) to using the longer one or should that be avoided?

Are the BBs you are looking at Campy? Your decision about what cranks to run will determine spindle length and BB type as the cranks really determine not just spindle length but also spindle type (spline, square taper, etc). I would guess that campy Bb with 115mm spindle would probably be right for Racing T but not sure.

Can't read? Use the 111 mm.

115mm is for chainstay clearance and will give poorer chainline. Yes it will make shifting less smooth, etc...

This is true only if the Racing T crankset OP will "probably be using" can be used with either of 111 or 115, and OP ultimately decides to use that crankset. So if in fact proper chainline with Racing T cranks can be achieved with either 111m or 115mm (I dont have specs handy), then OP should chose 111mm given the 28.6 seat tube. However, he should make final decision about what cranks he plans to use before deciding what BB to buy and check for certain what crankset manufacturer recommends for spindle length.

I have a very lightly used Campy AC-H 115.5 mm English threaded bottom bracket that was on my wife's 5200 Trek (big frame tubes)with Racing Triple. It sounds to me as if you need the 111 mm, but I would sell this for half price plus shipping if you're sure you want it.

Al