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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 12-19-08, 03:02 AM   #1
chore4n
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Yet ANOTHER Bottom Bracket question:

I'm running a stock Truvativ Powerspline BB 68x108 with Truvativ Touro 48t Crankset.

I'd like to replace both.

Would my chainline be affected if I got a BB that is 68x107?
I'm so new to Bottom Brackets, I'm replacing this BB/Crankset because it's a year old.
Or do I need to? I've ridden it hard since last January...

Any suggestions or advice is great help, thanks!
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Old 12-19-08, 03:46 AM   #2
darksiderising
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No, you don't need to replace them if there is nothing wrong with them.
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Old 12-19-08, 06:56 AM   #3
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Quote:
Originally Posted by chore4n View Post
I'm running a stock Truvativ Powerspline BB 68x108 with Truvativ Touro 48t Crankset.

I'd like to replace both.

Would my chainline be affected if I got a BB that is 68x107?
I'm so new to Bottom Brackets, I'm replacing this BB/Crankset because it's a year old.
Or do I need to? I've ridden it hard since last January...

Any suggestions or advice is great help, thanks!
First - why replace them? My roommate rode that crank/bb hard for three years without needing to replace it.

Secondly, this doesn't make any sense:
"Would my chainline be affected if I got a BB that is 68x107?"
Here's why. The spindle of a bottom bracket doesn't affect a chainline alone. It's the crank and spindle put together that determines how far away from the bike's centerline the chainring will be located. That is chainline. Asking if a bottom bracket will do something to your chainline is a meaningless question without saying anything about what crank you'll use.

Don't go out and buy a bottom bracket. Go out and buy a crank, and then buy a matching bottom bracket that will get you near enough to an appropriate chainline.

Some people get all anally retentive about chainlines, but getting within 2-4mm is plenty accurate.
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Old 12-19-08, 07:43 AM   #4
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Random fact, I measured the Touro chainline at 41mm (road standard for inner position). Most rear hub chainlines are 42mm plus the cog offset. For instance, my Formula with EAI cog yields a 43.5mm chainline.

And +1 to mattio.
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Old 12-19-08, 07:54 AM   #5
RoyIII
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Leave it alone, is my 2 cents. Instead of fooling with the bb, go out and ride!
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Old 12-19-08, 01:32 PM   #6
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If a bb doesn't last a year, something is truly wrong.

People have ridden 1+ year long trips from Argentina to Alaska on the same bb (with fully loaded bike).
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Old 12-28-08, 07:58 PM   #7
chore4n
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Okay, I've decided not to replace it.
But it feels so strange...and makes sounds that I've checked on Sheldon Brown's site, but I still haven't concluded what the sounds are.
Well, if it works don't jock it, right?
Thanks guys.
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Old 12-28-08, 08:12 PM   #8
Geordi Laforge
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what is the condition of the bottom bracket? what sounds are you talking about? are you sure the sound is coming from the bb? remove them and check.

if the bb is not serviceable and it's not spinning like it's supposed to, then yes, you should replace it with another.
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