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Discussion Starter · #1 ·
I feel this is an "inexperienced" or "newbie" question, hence it's palcement in this section.

I'm running 2009 SRAM Rival, and lan on swapping my 52/39 for a 50/36. I have only used my 52/39 for about.... thre or four months. This desired swapping has led me to the desire to ask questions.

1.) Would it be suggested to swap the BB's out when swapping the two different cranksets out? My doubt in this is that they are both GXP bottom brackets... I, personally do not see a big deal in keeping the bb as it is. Am I wrong?

2.) How should I go about lowering my FD to meet the needs of the smalelr chainrings.
  • Typically will I need a new cable?
  • What else should be done concerning the FD?
  • Is there different spacing on 52/39 and 50/36 chainrings that will need FD adjustment?
3.) Of course I'll need to shorten my chain, but what about anything else?

I know the process doesn't take more than an hour just like installing and cabling a new front end of a drivetrain, but I just don't want to miss anything silly. Can't blame me for wanting to be concise....

4.) What about frequent swapping while traveling to different areas? I know I will need to watch and torque correctly in order not to **** up the threading on my crankarm, etc and grease them each time... but will swapping them out three or four times a year be an OMG type increase in detrimental and undesired wear?
 

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Your current GXP BB should be fine w/the new crankset

For FD, since it's pretty new, you should be able to use the one that's on there now:
Detach the front cable and lower the FD (Parktools has good instructions on how to get it positioned right)
Re-attach the FD cable and adjust the high/low limits and shifting (after you get chain length right)
 

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1. You're right. No need to change BB.

2. Just move it, and adjust as necessary to get smooth shifting. The cable comes up from the bottom, and you'll move the der down, so you won't need a longer cable.

3. Not necessarily. You could only shorten it one link going from 52 to 50, and you may not need to at all. Try it first.

4. I don't know about that specific interface, but there might be some wear issues. If you're really going to do this frequently, you might think about investing in some 52/39 rings that will go on the compact crank. Switching rings takes a few minutes, but there's no danger of munging up an expensive part -- pretty much the only thing you could hurt is the bolts/nuts, which are cheap.

Or you could leave the 50/36 on all the time, and get a second cassette to give you the desired gear range when you want the taller gears. Cassettes are pretty foolproof to change.
 

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Discussion Starter · #4 ·
Werd. Somost of my precautionary ideas were right.

JCavilia - 110 bcd 52/39 chainrings - Links?

P.S. Andrea138 is a SRAM thread spy. And by spy, I mean great spy. :)
 

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I think it'll work fine, too. As far as swapping the crankset back and forth for different riding conditions, though, I can't see a reason to go to the trouble. I think you'll find the 50-36 more pleasant in ordinary riding, but unless you're consistently spinning out in your highest gear, there's no reason to change up when you go to Kansas. Any time I can turn a 52-11, I'm going to be coasting.
 

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Chain length

JCavilia said:
3. Not necessarily. You could only shorten it one link going from 52 to 50, and you may not need to at all. Try it first.
Actually, no. Changing chainring/cog teeth a total of 4 means one link. 2 teeth per inch, but only half of the teeth are engaged by the chain.
 

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