Front derailleur height with compact crankset?

Discussion in 'Cycling Equipment' started by slingus, Mar 13, 2005.

  1. slingus

    slingus New Member

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    I have a Litespeed Classic with a Dura-Ace braze-on front derailleur. With a 53/39 chainring, the FD looks like it is as low as possible on the braze-on tab. There looks to be about 2cm of cage below the small chainring.

    I am planning on switch to a 50/34 FSA SLK compact crankset. Will I need to lower my FD height? Anybody have experience with this? I don't want to go out an order a new crank that won't work on my frame. Experiences with compact crank install with braze-on FDs?
     
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  2. boudreaux

    boudreaux New Member

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    Yes..............
     
  3. hockey

    hockey New Member

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    Yes, you will have to lower the FD. I had no problem with this issue but you may have to file a groove in the bracket to allow a greater drop. I understand Shimano also sells a new bracket for this setup.
    Good luck.
    Hockey
     
  4. boudreaux

    boudreaux New Member

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    A new bracket will do one no good if the tab is brazed or welded on. I thought the Classic used a clamp on FD anyway.
     
  5. slingus

    slingus New Member

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    I'm not sure if current Classics have braze-on or not, but mine certainly does. It is circa 2000-2001. I used to be a huge fan of braze-on FD, but am having second thoughts.

    I know that I would probably need to lower my front derailleur if it was currently set up at the right height. I'm hoping that the current height was set on the low side by whoever installed it originally. From what I have seen on the boards, a braze-on should be able to support a 48 or 50 tooth large chainring. Is this reasonable?

    That or notch the tab down a bit as suggested....
     
  6. rv

    rv New Member

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    I ride a 2000 classic and have had a fsa carbon compact (octalink) for about 15 months. no problem with the braze on fd as mine shifts pretty darn well. don't know if its all the way down or not - the shop set it up - since I can't tell by looking.
     
  7. boudreaux

    boudreaux New Member

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    That depends.They are not all the same. A 50 would be a reasonable assumption for most,but a 48 a real stretch for many.
     
  8. Gonzo Bob

    Gonzo Bob New Member

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    A 53T chainring has a circumference of about 53/2 inches and a radius of about 4.22 inches or about 107mm

    A 50T chainring has a circumference of about 50/2 inches and a radius of about 3.98 inches or about 101mm.

    So ideally you'll want to lower the front derailer by about 6mm. That's what I did when I went from 39/53 to 34/50.
     
  9. hockey

    hockey New Member

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    bourdreaux. I was referring to the slot adjustment on a braze on derailleur. Shimano makes a fix for this part which is attached to the braze on. Sorry about the vocab.
    Hockey
     
  10. boudreaux

    boudreaux New Member

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    Still don't get it.
     
  11. slingus

    slingus New Member

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    I sent an email to Litespeed customer service about this issue. The reply I got was that a compact crank requires a longer braze-on that what they used to build Classics with. So, RV you may have gotten lucky that yours installed without a problem.

    He recommended that if I wanted to fix this problem then to send the frame/bike in to the factory to either 1) remove the braze-on tab and use a clamp on adapter or 2) replace with a longer braze-on tab (at additional charge). Both of these options would retain the frame warranty.

    However, seems by RV's experience there may be a chance that I can get a 50/34 on without any modification.
     
  12. hockey

    hockey New Member

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    Absolutely. Those having problems with FSA mega cranks have been advised to leave a larger spacing between the derailleur and the crank.
    Hockey
     
  13. rv

    rv New Member

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    mark your fd position, then see if you can move it down. that should be a better indication of whether or not it will work.
     
  14. boudreaux

    boudreaux New Member

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    That's too friggin simple.
     
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