Bicycle Mechanics - Choosing the right bottom bracket...HELP!
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06-12-06, 12:00 AM
I have a 1989 handbuilt Davidson Impulse (Bill Davidson Frame of Elliott Bay Bicycles - Seattle). It's been suggested to me that I should upgrade the old Shimano 105 cranks to something like a newer Ultegra Double crank set. I'm very inexperienced in bicycle mechanics but am willing to try. My question is, if I try to buy something on Ebay, etc. how do I know (or measure) what size/type of bottom bracket I need? I do know that there is either square shaft or octalink, but I don't know how to tell the correct dimensions. I understand that how far the bracket sticks out affects the chainline and can cause issues. Is there an easy way to figure this out? Is it pretty standard stuff? How difficult is it to replace this all on my own, or is this a LBS project? Thanks for your suggestions!
06-12-06, 02:02 AM
The first thing you need to do is figure out what threads the frame has.
Clean off the outside of the old bb real good. you will probably see some lettering and numbering on it.
Find those, write them down, then post them here.Someone will be able to tell what you have.
Do you currently have the 105 Triple?
If that is the case then you will need a different length bb.
When you find out what threads your frame has, the place where you purchase the cranks can tell you what BB you need along with the tools. It's not hard at all.
I just changed the cranks on my 1994 Bridgestone RB1. I went from the ugly silver painted
105 Double(#FC1056) to an Ultegra FC6500 Double.
I was just looking to replace them with another 105 set or a low end campy set.That's when I found a sweet deal on a FC6500 crankset.
I also noticed that I didn't like the looks of the newer crank sets from Shimano.
Take a look at the newer FC6600, it just don't have the same look.
I think It's kinda ugly and didn't really fit the vintage of my bike.
The FC5500, FC6500, FC7700-FC7701 are much better looking to me and also have a more vintage look.
They are less efficient at transferring the power then the newer design though.
Another thing to keep in mind is that the newer cranksets like the fc6600 are designed for a 10 speed cassette out back.This means that they will not be an exact match for your bike's rear cassette.
Both the 9speed FC6500 and the FC6600 have a chainring spacing that is, I believe a bit tighter together.
I asked for advice here and on other boards and was told the 9spd fc6500 that I chose probably wouldn't give me any problems, but I have an 8spd rear cassette. If you have a 6 or 7spd cassette you may have a problem with either crankset that I mentioned.
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