42T 1x Chain Ring for '98 Marin Pine Mountain- Mtbr.com
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  1. #1
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    42T 1x Chain Ring for '98 Marin Pine Mountain

    Recently purchased SRAM Apex 1x11 groupset for a 1998 Marin Pine Mountain that I'm converting into a grave/CX/Frankenstein. The cranks have a 42T chain ring and 175mm arms. It didn't fit properly with 1-3 spacers on the BB and eventually started binding up the bearings on the BB to the point that it just didn't spin.

    Took it to LBS and they said it's not going to work. Not sure if the spindle length is too short, the diameter of the chain ring is too large (it's hitting the chainstays with no spacers on BB), or if the crank arms are too long - or all of the above. I really want to stick with 42T in the front to pair with the 11-42 in the back.

    Can anyone recommend something that will work?
    Attached Thumbnails Attached Thumbnails 42T 1x Chain Ring for '98 Marin Pine Mountain-img_8807.jpg  


  2. #2
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    If you're running a 1x, you would ideally want to line up the chainring with the middle of the cassette for good chain line.

    That will mean the chainring would be somewhere in the vicinity of the middle ring position if you were using the original 3x crank and BB.

    MTB chain stays tend to flare out dramatically to clear knobby treads, so a 42t in the "middle" position is, in most cases, not going to fit. Also, you're dictated by the length of the crank spindle, moving the BB out by adding spacers on the drive side isn't going to do anything except cause interference between the crank and the BB.

    Option 1 - keep the original crank and BB and run a 42t in the middle position, which may still hit or go close to the chain stay.

    Option 2 - keep the original crank and BB and run a 42t in the outer position, which may result in a poor chainline when running 42-42.

    Option 3 - set up the Apex crank with a smaller chainring.

    Sorry, I know it isn't what you wanted to hear.

    Grumps

  3. #3
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    I appreciate the reply. I'm looking at the GRX gravel specific group. Do you think the geometry of GRX would be more in tune with the geometry of an MTB chainstay?

    I'm not sure what spec I should be researching so I can compare. Is it the chain line dimension? I saw +2.5mm or +2 but I don't really understand that.

    IF that were to work, I feel like mixing Shimano and SRAM cassette/chains/chainring might not be happy.

    There's gotta be some product out there.

  4. #4
    Phobia of petting zoos.
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    Mixing SRAM and Shimano cassettes, chains and chainrings will be the least of your problems. SRAM and Shimano only refuse to play with each other when it comes to shifters and rear derailleurs.

    It is the chainline that is the issue.

    Like I said, the chainline needs to align "roughly" with the middle of the cassette. Once you have that, you can work out what size ring will fit and I'm wagering it will be less than 42t. I know, it's hard to estimate this kind of stuff when you're trying to align stuff in mid air.

    I'm not familiar with the GRX group. But if it is designed for cross or gravel use it would work with a dedicated frame that, when compared to a 26" MTB, will have narrower stays.

    As for there being "some product out there", you're looking for something that will allow a larger chainring ring to work in the middle ring position without chewing the chain stay. There is such a product, it's called a new frame with narrower stays. Or the other product is called a 34t chainring.

    Otherwise, I would be setting up the bike with the old cranks and BB and dummying up the big ring in the middle position to see what kind of clearance you have. If that doesn't work and I'd bet it won't, try the chainring in the outer position and see how bad the chainline is when in the granny gear.

    I have set up bikes with all sorts of drivetrain combos on various frames over the years. Sometimes, some combos just don't work. I learned early on the "road" gearing on an MTB was one of the combos far less likely to fit.

    Grumps

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