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  1. #1
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    swapping

    i have a MTB and a road bike. is it ok for me to move the chain, rear derailleur or maybe even the cassette to my road bike? It seemed like my MTB's rear derailleur has long arm, and my road bike has short arm.

    i'm not sure if they have the same gears.

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    Senior Member Steev's Avatar
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    Do both bikes run Shimano or compatible components?
    The derailleur cage length is not important.
    The cassette needs to have the same number of cogs as the shifter is made to shift.
    The chain may not be long enough, in which case you need to replace it. Check the chain wear, if its worn its not worth changing over. Otherwise it should work fine.
    If the road bike has 9 or 10 speed rear, the chain must be specific to 9 or 10 speed, not an issue if you swap both chain and cassette.

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    Quote Originally Posted by Steev View Post
    Do both bikes run Shimano or compatible components?
    The derailleur cage length is not important.
    The cassette needs to have the same number of cogs as the shifter is made to shift.
    The chain may not be long enough, in which case you need to replace it. Check the chain wear, if its worn its not worth changing over. Otherwise it should work fine.
    If the road bike has 9 or 10 speed rear, the chain must be specific to 9 or 10 speed, not an issue if you swap both chain and cassette.
    The RD cage won't be an issue if going to a longer cage. Going to a shorter cage, you have to consider if the new cage will have enough take-up capacity for your gear combination.

    Unless your chain has a reusable connector, I don't suggest moving it over. Chains are cheap enough anyway.

    Otherwise it's as Steev says, that barring some obvious incompatibility like a Shimano cassette/Campy hub, or 9s system/8s cassette, there's no reason MTB components won't work on road, or vice versa.
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    Quote Originally Posted by Steev View Post
    The derailleur cage length is not important.
    Not true in general, but it's OK for him. The cage has to be long enough to "wrap" all the gears. The important issue is tooth capacity, which determines how much the rear derailer can expand to take on a wider range of gears. For optimal safety, tooth capacity is measured as the (large chainring + largest sprocket) - (smallest chainring + smallest sprocket). You can get away with a RD that has less capacity than recommended by the manufacturer if you're certain you can stay out of the big-big combo, and preferably the small-small as well.

    In his case, taking a mountain RD to a road bike will work great, but the opposite won't work so well. Many people do what the OP's doing to make a bike that can work for a wide gear range.

    Using the mountain RD and cassette will be great. The chain may or may not be usable depending on length.

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    Quote Originally Posted by Mr. Underbridge View Post
    Not true in general, but it's OK for him. The cage has to be long enough to "wrap" all the gears. The important issue is tooth capacity, which determines how much the rear derailer can expand to take on a wider range of gears. For optimal safety, tooth capacity is measured as the (large chainring + largest sprocket) - (smallest chainring + smallest sprocket). You can get away with a RD that has less capacity than recommended by the manufacturer if you're certain you can stay out of the big-big combo, and preferably the small-small as well.

    In his case, taking a mountain RD to a road bike will work great, but the opposite won't work so well. Many people do what the OP's doing to make a bike that can work for a wide gear range.

    Using the mountain RD and cassette will be great. The chain may or may not be usable depending on length.
    The reason i wanna swap them is because i want my road bike to be BETTER. Is MTB rear derailleur, long cage, better than short cage? what are the characteristics?
    ALso it goes for the cassette, what's the point of swapping the same number of gears if my road bike's cassette is in good condition.
    I want my bike to perform better than now.

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    Quote Originally Posted by kris cho View Post
    The reason i wanna swap them is because i want my road bike to be BETTER. Is MTB rear derailleur, long cage, better than short cage? what are the characteristics?
    ALso it goes for the cassette, what's the point of swapping the same number of gears if my road bike's cassette is in good condition.
    I want my bike to perform better than now.
    Better how? better is defined differently depending on specific needs. Are you looking to upgrade the RD with one that is comparably higher on the price/quality scale, ie a top end ATB derailleur vs. a low end road model? Are looking to widen the range of gearing?

    If you're hoping to magically improve on an already OK system without a specific goal, I think you'll be disappointed. Overall, at the same quality level, I usually suggest the shortest cage RD with sufficient capacity. Shot cage RDs usually ride closer the the cassette and therefore offer more responsive shifting.
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    Quote Originally Posted by FBinNY View Post
    Better how? better is defined differently depending on specific needs. Are you looking to upgrade the RD with one that is comparably higher on the price/quality scale, ie a top end ATB derailleur vs. a low end road model? Are looking to widen the range of gearing?

    If you're hoping to magically improve on an already OK system without a specific goal, I think you'll be disappointed. Overall, at the same quality level, I usually suggest the shortest cage RD with sufficient capacity. Shot cage RDs usually ride closer the the cassette and therefore offer more responsive shifting.
    i'm looking for what's efficient when climbing hills.fast respond.better gearing.

    If short one is better than why do MTB have longer cages?

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    The cage length determines the chain wrap capacity. Longer cages take up more chain, it's that plain and simple.

    To calculate how much capacity you need, add the difference between your largest and smallest chainrings, to the difference between the largest and smallest cassette cog. ie. 39-53. w/ 12-28 cassette = 14t + 16t = 30t capacity needed.

    No offense intended, but given the questions you're asking, I suggest you find a local friend to look over your wheels, and make suggestions, before you invest time and effort in the wrong direction.
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    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

  9. #9
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    Quote Originally Posted by kris cho View Post
    i'm looking for what's efficient when climbing hills
    Generally, a stronger rider is better for climbing hills fast. If you wanted to climb hills with less effort (and generally less speed) you would want a triple in front or a compact double. In your case you might be better off with a compact double, and you may need to get a new FD or RD in that case.

  10. #10
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    Quote Originally Posted by FBinNY View Post
    The cage length determines the chain wrap capacity. Longer cages take up more chain, it's that plain and simple.

    To calculate how much capacity you need, add the difference between your largest and smallest chainrings, to the difference between the largest and smallest cassette cog. ie. 39-53. w/ 12-28 cassette = 14t + 16t = 30t capacity needed.

    No offense intended, but given the questions you're asking, I suggest you find a local friend to look over your wheels, and make suggestions, before you invest time and effort in the wrong direction.
    how about this. what if i swap the pulleys? do number of teeth matter when i swap?
    Can't i just swap and use the same chain?

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