Bicycle Mechanics - BB dimensions
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So I am planning on replacing my BB and chainrings and now just read the helpful advice re: just buy an entire crankset with rings, it may be cheaper.
So now I wonder if I still must purchase the 118 mm spindle length BB as was the original or do I match the spindle length to the new crankset, which may be different?
Welcome to the Forums! Glad you found us. Hope you'll share more questions and ideas with us. Pics are also a welcome sight. You're the first, that I know of from Saipan.
If you are up-grading your cranks with an expensive pair, then you will have to change spindle length. The Mfgr of the cranks will say which size to use. You will also need to know the BB Shell size --68, 70, 72mm.
However, if you are just replacing them with the same brand, then keep everything as is.
01-01-02, 11:18 AM
Another thing that can arise with bb is threading - English or Italian. It's easy enough to tell. Italian threading both sides thread in clockwise, ie, "normal". English, one side threads in clockwise, one counterclockwise. Also make sure the crankset and bb you purchase are compatible. Modern Shimano cranks require a modern splined-spindle Shimano bb, and the Shimano mtb spline is apparently different from the road spline. Older "traditional" cranks use a square, tapered spindle. Other than Campagnolo, the tapered square spindle is almost universal, ie, you can mix and match bb and crank brands. Campagnolo is also a square, tapered spindle, but the taper is slightly different so you must use Campy/Campy. For the most part you can mix models with Shimano. For instance, use an Ultegra bb with a 105 or Dura Ace crank. In fact, many recommend using the Ultegra bb with the DA crank because the Ultegra bb is more durable. Forgive me if you already know all this; just trying to help.
Spindles come in a few 'common' sizes, so it would be best to stick with the length that you currently have (or else your chainline will get screwed up). A few manufacturers offer odd lengths-buy one of these only if a common size is a problem for your application.
There is one more unwelcome variable here: how deeply the crank seats onto the spindle. I replaced the conventional BB on my son's Specialized Hard Rock mountain bike with a Shimano UN-72, which messed up his chainline because the (Shimano!) cranks did not seat all the way onto the tapers. I salvaged the situation by moving the UN-72 to my aluminum-framed Ross (73mm vs. 68mm BB shell width), and buying a shorter-spindled UN-72 for the Hard Rock.
01-01-02, 04:44 PM
Don't bother with a new crankset, unless it's a signifcant and NEEDED upgrade. Save your money, going that direction is often more expensive.
Originally posted by pat5319
Don't bother with a new crankset, unless it's a signifcant and NEEDED upgrade. ...
Having broken two cranks while cycling, I don't think a new crankset is always a waste of money.
The crankset idea was from a post that explained that it may be cheaper then three new rings, and sure enough there is a deal on an LX hollow crank set for $50 at Jenson's (In the hot deals forum), however these are 9 speed rings and you have to get the BB that matches for another $24, but still good value.
Since I run 7 speed and now understand a bit more about chainline, will stay with the cranks I got and get Nashbar rings.(unless someone tells me quick that they are crap.
Its hard to find 7 speed stuff, which is why the Nashbar rings. I was tempted to take advice that says to just go with 9 speed rings cause they're simply narrower but should still hold the wider chains.
Thanks for the other advice, though I did figger out I have 68 mm English threads and a 118 mm spindle.
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