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Upgrading Bottom Bracket(8 posts)

Upgrading Bottom Bracketkwbreezer
Apr 8, 2002 6:06 AM
I have an italian road bike that I have had since the late 80's. I am upgrading the components and need some advice regarding the bottom bracket. It has an old style cup and cone BB with 115 mm square ended spindle. My new shimano cranks are splined and I need to find a compatible sealed cartridge BB. It needs to have italian threads, which shimano says they make, but the spindle lengths are 109.5 or 118 mm. Considering the original was 115 mm, which size am I better to go with, 109.5 or 118mm?

Any help would be appreciated.
re: Upgrading Bottom Bracketxxl
Apr 8, 2002 6:20 AM
The best way to resolve this problem is to order both sizes, with the intention of returning the one that doesn't work, or gives a less-than-optimal chainline. It's hard to say which will fit better: both may work; the 118 will almost for sure fit(but may mandate some minor derailleur tweaking); the 109.5 may also work, or may cause your rings to rub on the chainstay. You could take measurements, but the accuracy factor here is way low. Best to try empirically. The general rule is to run the shortest spindle you can get away with (i.e., that leaves your chainrings at least a few millimeters from the d.s. seatstay, and remember you'll be flexing this under loads, so be a bit generous). And remember that you can adjust the chain line.

BTW, I think Shimano makes the UN-BB-72 in a 113, which would be more likely to work than the 109.5. Other makers offer sizes close to 115 as well.
re: What!!!Rusty Coggs
Apr 8, 2002 8:14 AM
Ya don't return used BB.The un-72 is not splined.
re: What!!!xxl
Apr 8, 2002 12:28 PM
Sorry, must've been a flashback moment; lost the part about the new crank being splined. You are correct.

I wouldn't use the BB, just fit it "on the stand." You should be able to tell if it'll fit without harming its salability, no?
re: Upgrading Bottom Bracketlaffeaux
Apr 8, 2002 7:12 AM
Splined BBs benerally run slightly longer than tapered. If your bike worked well with the 115, then the 118 mm splined is what you need. The 118 is generally used on bikes with triples.
re: HFC......Rusty Coggs
Apr 8, 2002 8:11 AM
If your Shimano splined crankset is a double,go with the 70x109.5,if it's a triple then use the 70X118.5.Simple...no?You go with a new BB spindle length and type that matches the NEW crank!
re: Thankskwbreezer
Apr 8, 2002 8:47 AM
Found a local bike shop with both 109.5 and 118 in stock. As was the consensus here, 109.5 is likely the one for me, but they said I could try both and return one.
Just to be clearKerry
Apr 8, 2002 4:53 PM
Though it was alluded to in some other posts, you must recognize that axle length is only meaningful in the context of the particular crank you are using. A 113 in a crank with no offset may be equivalent to a 103 in a crank with a lot of offset. You can't compare lengths except to look at the different lengths available for a given crank. And many sets these days have a double and triple length, so you don't need to worry except that you got the right one. You can always adjust chain line with a spacer on the right side if you fall between lengths.