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Old 07-31-09, 01:46 AM   #1
calyth
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Would going from an internal BB to external BB severely affect chainline?

Hi,

My friends got me a FSA Omega compact double for my birthday (I live in a hilly area, and 39-26 can overcook my cardio), and of course, I wouldn't mind swapping the Ultegra 6500 crankset off my Cannondale R2000 '99 vintage.

Question is, the chainline on my bike right now looks great. It's maybe about 1 mm off from the front to back (using the accurate method outlined by Zinn and Road Bike maintenance using a decent caliper). But wouldn't using an external BB crank severely affect the chainline? Or am I missing something obvious?

Also, if anyone can confirm that the R2000's BB shell is 68mm wide would be great. I can't measure it until I take the cranks off and I'm hoping someone would know so I don't have to

Thanks lots!
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Old 07-31-09, 02:36 AM   #2
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The crank and BB are designed as a system to put the chainline where it's supposed to be, so it shouldn't be off, providing the frame is machined correctly and manufacturer's varying standards notwithstanding... see http://www.sheldonbrown.com/chainline.html
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Old 07-31-09, 03:16 AM   #3
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Yep. I changed a Shimano Octalink out for an Ultegra BB Hollowpoint setup. I had measured the chainline. It was 45mm to begin - and it was 45mm after I finished the operation. Just watch and measure as you proceed.
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Old 07-31-09, 07:40 AM   #4
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It will work. Just a week ago or so, I put on an external from square taper. Works fine. Well, I put the spacers on the wrong side at first and it would shift spontaniously, but apart from that
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Old 07-31-09, 07:49 AM   #5
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And yes, the BB shell will be 68mm on a Cannondale road bike.
I don't see why you can't measure this with the BB installed.
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Old 07-31-09, 08:32 AM   #6
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soooo....can I have the FC6500?
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Old 07-31-09, 05:43 PM   #7
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No, the chain rings were in the way, and I didn't have all the tools necessary to take the cranks off to measure the BB.

Reason why I asked is that the compact crank and external BB was 2nd hand, and there wasn't spacers for the BB. Looking at the instructions, it says that anything bigger than 68mm would require spacers.

Thanks all for the insights!
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Old 07-31-09, 06:24 PM   #8
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If 39-26 is "overcooking your cardio" like you said, then 34-26 will do it even worse.

Low cadence puts more strain on muscles but less on heart.
High cadence lets your muscles rest a bit, and will "feel easier", but generally increases heart rate.
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Old 07-31-09, 07:01 PM   #9
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^ I rather have a lower cadence. I don't mind the mnuscle pain but its the heart that I don't like having jump around.
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Old 08-01-09, 01:16 PM   #10
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Quote:
Originally Posted by calyth View Post
No, the chain rings were in the way, and I didn't have all the tools necessary to take the cranks off to measure the BB.

Reason why I asked is that the compact crank and external BB was 2nd hand, and there wasn't spacers for the BB. Looking at the instructions, it says that anything bigger than 68mm would require spacers.

Thanks all for the insights!
Sounds like you're confusing bb shell width (the 68 or 73 that are most common) with spindle length. Just measure the width of the shell at the bottom, nothing should be interfering with your measurement there. Spindle length is a no-brainer with an external type as it's fixed.
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Old 08-01-09, 11:37 PM   #11
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Quote:
Originally Posted by pacificaslim View Post
If 39-26 is "overcooking your cardio" like you said, then 34-26 will do it even worse.

Low cadence puts more strain on muscles but less on heart.
High cadence lets your muscles rest a bit, and will "feel easier", but generally increases heart rate.
Well, when it's a particular steep hill, my heart rate pops over 185bpm, with heavy breathing and all, even though my cadence is down to like 60rpm (sometimes less on really nasty stuff that I ran across with my heart rate monitor on). And I've tried pacing it with an even slower cadence.

Yes, I know that means I'm just out of shape, but sometimes I do have to deal with those hills. I would prefer to be able ride over the hill instead of stopping.
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Old 08-01-09, 11:39 PM   #12
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Originally Posted by bikinfool View Post
Sounds like you're confusing bb shell width (the 68 or 73 that are most common) with spindle length. Just measure the width of the shell at the bottom, nothing should be interfering with your measurement there. Spindle length is a no-brainer with an external type as it's fixed.
No I tried to measure the shell (which is obviously connected to the frame), and not the parts of the cartridge BB. I didn't have a ruler handy, and I just couldn't get the calipers in at the right place. Mind you I was trying to do that at 1am, so I didn't try very hard.
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