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  1. #1
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    The MTB/road front derailer discrepancy

    What is the exact reason I couldn't/shouldn't run a road derailer with a mountain shifter, or vice versa?

    The only reason I can seem to find is the lack of a trim click on the MTB shifter.
    All the knowledge in the world is of no use to fools.

  2. #2
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    They use different cable throw.

  3. #3
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    Can't be, Shimano's flat bars road shifters are listed to work fine on MTB setups. And I'm sure I've seen some entry level hybrids running mixed setups.

    Shimanos only mention on their site
    " Can I use my road levers with a mountain bike front derailleur?
    No. Due to the different actions within the shifters, these components do not work well together."

    From BTI's discription for the R660 and R440 flat bar road shifters.
    " Designed as flat-bar road shifters, but can be used for mountain: extra front shifter 'trim' compared to mountain specific rapidfire shifters"

    Seems like another one of those that will work, maybe not as well, but they don't want you running.
    All the knowledge in the world is of no use to fools.

  4. #4
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    GripShift uses a trim feature if you were that way inclined.

    A lot of guys running a 2x9 set up on their MTB run a road derailleur for the weight saving. Being only 2 chainrings the derailleur is either at the inner limit or pulled to the outer limit, there is nothing in between to index so the cable pull ratio doesn't matter.

    With a triple ring, it gets a bit fussy.

    Also, road derailleurs are bottom pull, a lot of MTBs are top pull.

    I have a commuter with MTB shifters working a road derailleur, on a road double ring set up. All works fine, but again, it's 2 chainrings and not 3.

    Grumps

  5. #5
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    If you are running nine speed, they should be interchangeable. However, your choice of front derailluers may depnd on what crankset you are running. A MTB derailluer will be designed for a 44 tooth chainring, whereas a road derailluer will be disined to work with a 53 tooth ring. You can use lareger or smaller with either, as evidenced by ther not being seperate front derailluers for compact vs standsrd cranks, but the difference between a 44 tooth ring and a 53 tooth ring is significant, so the arc of the cage will be different.

  6. #6
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    All other parts aside, if you were to want to put drops on a MTB or MTB bars on a rodie you should be able to pick shifters to match the bars (STI or MTB pods) and not run into any problems?
    All the knowledge in the world is of no use to fools.

  7. #7
    Number 2 on the course.
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    Quote Originally Posted by big_papa_nuts
    All other parts aside. . .
    That stipulation makes the statement false (or the question unanswerable).

    It can work, provided that all the parts are compatible.

  8. #8
    Old, slow, and fat.
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    Quote Originally Posted by big_papa_nuts
    What is the exact reason I couldn't/shouldn't run a road derailer with a mountain shifter, or vice versa?

    The only reason I can seem to find is the lack of a trim click on the MTB shifter.
    You can get em to work well together, but it ain't perfect.

    If ya want perfect, stick with like-like

    M
    I've moved back to NoVA. PLEASE change the weather!

  9. #9
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    In my experience with mixing road and mountain components (mostly for touring and cyclocross bikes), the FD is usually the component that has the most compatibility issues (followed by brakes). In no particular order, some issues you may encounter include: cable pull ratio, clamp size, clamp interference with the bottle cage bosses, clamp interference with rear tire or fender, cage interference with chainstay, max chainring size and size difference between outer and middle ring, max range between outer and inner rings, and chainline. If the chainline is too big, such as on a 50mm MTB crank, a road FD might not be able to reach the outer ring. If it's too small, or your seat tube is too big, the FD might not be able to move inward enough to reach the inner ring. I've run into almost all of these problems myself, and I've only got a few bikes, though I do tinker quite a bit.

    Ironically, though the RD seems more complex, it often just works as long as you stay within one manufacturer and don't greatly exceed its chain wrap or max cog capacity. Modern FDs, on the other hand, are often closely matched to a particular crankset with a specific combination of chainrings and chain width (especially Shimano triple FDs).

  10. #10
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    Quote Originally Posted by PeanutButterBreath
    That stipulation makes the statement false (or the question unanswerable).

    It can work, provided that all the parts are compatible.
    Ok, then lets make this simple...say we have a road bike set up with a triple crank (together and in working order and using "road" shifters, specifically brifters) and we wanted to take off the drop bars and put on a set of flat bars. Would you be able to simply switch to MTB shifters and have it work fine (aside from a trim function)?

    Or...let's say we have a MTB with a triple (together in working order with MTB shifter pods) and we would like to install drop bars and a set of brifters (for a triple crank of course). Could we do that and have it work fine?

    The basic question is do road and MTB shifters pull the same, or close enough to work, amount of cable per shift?
    All the knowledge in the world is of no use to fools.

  11. #11
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    Quote Originally Posted by big_papa_nuts
    The basic question is do road and MTB shifters pull the same, or close enough to work, amount of cable per shift?
    To my mind, it's close enough.

    You have consider how they work. There is an inner limit stop that you set relative to the inner chainring when in small-big. You have an outer limit that you set relative to the outer ring when in big-small.

    The middle is the issue, and it is set by the cable tension as the derailleur either drops into position (and is "caught" by the cable) or pulled into position.

    So it stands to reason that the outer and inner are easy enough ti set up. And the middle should be able to get close enough with cable tension. The worst that can happen is the cable is a bit slack when in the inner position.

    In other words, close enough to operate fine, by my reckoning.

    I'm sure someone will argue this and probably even prove me wrong.

    Grumps

  12. #12
    Probably slower than you.
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    +1 on grumpy's statement.

    make it work. too many people are too picky about what "works" when they really are just following mfr's suggestions and have never tried the combo themselves. in the great words of Nike... Just do it.

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