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  1. #1
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    xt front derailleur- 9/8 spd

    ive always heard that it doesnt matter what drivetrain (8/9) you ride, the front and rear derailleurs are "dumb" components. i just got a new frame and need just my derailleurs now to finish it. im planning on stickin with just 8. all discriptions that ive seen for derailleurs say theyre designed for 9 speed systems. does that matter? how do i figure out my clamp size? measure circumference and figure out diameter in mm?

  2. #2
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    The front derailleurs are 7/8 or 9 speed specific. The side plates on the 7/8 speed derailleurs are further apart to accomodate the wider 7/8 speed chain and the wider spacing of the chainrings on the 7/8 speed crank. If you use a 9 speed deraileur with a 8 speed drivetrain, you will have a lot of gear combinations where the chain rubs on the derailleur.

    You get the clamp size by measuring the seat tube with vernier calipers.
    There is no added value to my participation - in fact, just more confusion.

  3. #3
    JmZ
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    Quote Originally Posted by GearHead
    The front derailleurs are 7/8 or 9 speed specific. The side plates on the 7/8 speed derailleurs are further apart to accomodate the wider 7/8 speed chain and the wider spacing of the chainrings on the 7/8 speed crank. If you use a 9 speed deraileur with a 8 speed drivetrain, you will have a lot of gear combinations where the chain rubs on the derailleur.
    I took a set of calipers to a rear mech when 9 speed first came out. Unless they've gotten narrower since then the difference in the cage width was less than a millimeter.

    I'm using a 9 speed front mech, and a 9 speed rear mech on three bikes with no problems.

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  4. #4
    Linoleum Knife
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    Quote Originally Posted by laackund
    ive always heard that it doesnt matter what drivetrain (8/9) you ride, the front and rear derailleurs are "dumb" components. i just got a new frame and need just my derailleurs now to finish it. im planning on stickin with just 8. all discriptions that ive seen for derailleurs say theyre designed for 9 speed systems. does that matter? how do i figure out my clamp size? measure circumference and figure out diameter in mm?
    I've had problems with using 9-speed front d on a 7-speed system, but used 7-speed on 7, 8 & 9 with no problems.

    You should be fine.

  5. #5
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    Quote Originally Posted by forkboy
    I've had problems with using 9-speed front d on a 7-speed system, but used 7-speed on 7, 8 & 9 with no problems.

    You should be fine.
    I believe he wants to use a 9 speed front derailleur on a 8 speed bike.

    I measured my 7/8 speed front derailleur, it is 13 mm between the buldges in the side plates and 12 mm on a 9 speed front derailleur. So, the 7/8 speed is 8% wider which seems to be what is required for a chain that is 0.5 mm wider and chainrings that are also about 0.5 mm further spaced apart.
    There is no added value to my participation - in fact, just more confusion.

  6. #6
    Linoleum Knife
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    Quote Originally Posted by GearHead
    I believe he wants to use a 9 speed front derailleur on a 8 speed bike.

    I measured my 7/8 speed front derailleur, it is 13 mm between the buldges in the side plates and 12 mm on a 9 speed front derailleur. So, the 7/8 speed is 8% wider which seems to be what is required for a chain that is 0.5 mm wider and chainrings that are also about 0.5 mm further spaced apart.
    Ahh - my comprehension switch was in reverse

  7. #7
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    I ran 9 speed front/rear deraileurs on an 8-speed bike for three years without any problems.

    I do however, now experience front deraileur rub on my all 9-speed system. Go figure......
    It's only pain......

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