Chainline Adjustability of XT Cranks- Mtbr.com
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  1. #1
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    Chainline Adjustability of XT Cranks

    Hey there, I just got a new Trek Scratch 7, and since I can't ride it for a few more weeks (too much snow) it's a good time to mess with parts. The bike comes with Race Face Ride AM cranks, which are great, but aren't quite an exact match to my preferences in crank length and weight. I'm hoping to put new XT's on the bike. My question is that with a 73 mm bb shell running an MRP long range patrol tensioner can I get the chainline adjustability that I need to run XT cranks? I had a hell of a time getting the stock Race Face cranks to run without rubbing. I had to max the spacing out all the way toward the drive side, put a thinner O ring seal on the non drive side, as well as flip the roller, just to gain enough clearance. I'd tried to set up a pair of XT's on an SX Trail a few years ago and found they lacked the adjustability to work with a dual ring tensioner, but was hoping the newest generation of XT's could make this happen.
    Thanks for any help.
    Austin

  2. #2
    Deadhead
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    The XTs won't have the adjustability of the Race Face offerings. I ran into a similar problem with XTs and SLXs using ISCG and BB mount Blackspire Stingers. I got everything worked out, but the roller isn't exactly where I'd like it to be. I can't comment on the MRP pieces.
    "If you can get both wheels sliding with no brakes, that's when you really know that you're cookin." Nathan Rennie

  3. #3
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    I am failing to understand this question. Your chainline has nothing to do with any guide system...it is a simple measurement dictated by your frame and rear hub combo. Putting a guide of any type has no effect on the chainline and you should in no way adjust your chainline because you are installing a guide....

    As to the blackspire, that is an issue of the poorly chosen bolts that blackspire has decided to use/design around. Moving your cranks outboard and making your chainline worse (99% of cranks are at least 2.5mm wider than THE chainline of a 'normal 135mm rear hub..of exactly 47.5mm) is not a solution to a poorly designed chainguide.

    No idea if the MRP uses countersunk flat head mounting screws as they dont include that sort of information anyhwere in the product description or instructions.

    A properly designed chianguide will not protrude further (be thicker at any point that could interfere with the crank) than the 2.5mm BB spacer that is part of the crank instalation. Every single three ring crank has the same ring mount to ring mount spacing, and thus the clearance needed is exaclty the same crank to crank. It should not be so difficult for guide mfg to figure out the clearance and spacing issues, but apparently some are still stuggling with this...

  4. #4
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    Regardless of technical terminology, the info I'm looking for is do XT Cranks have enough chainline adjustability to properly position the drive side crank in relation to a LRP boomerang/roller and bash ring. Race Faces claim 3mm of (what they also call) chainline adjustability, and again I realize that chainline (in relation to where your cassette is positioned) is not directly related to this, but the drive side cranks inboard-outboard adjustability is. Any one running this? What to expect?

  5. #5
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    Regardless of what's considered ideal, you should be able to get the XT cranks to work out fine with a 2 ring and pulley setup. The XT's come with a spacer on the drive side that you can replace with the backplate. I have the same setup and it fits well.

    You don't have any way to cheat the system with XT like you supposedly do with Race Face- but as you have found out the Race Face cranks have to be maxed out with their adjustability just to get the granny bolts to clear the backplate. With the XT'as the bolts will just clear the backplate, but that doesn't really leave any room for ISCG bolts. I use a BB mount backplate and run just one bolt through the lower tab- backwards into a hole i drilled into the backplate to keep it from rotating on impact. The bolt doesn't thread into the backplate, it judt sits in the hole, and is threaded into the ISCG tab.

    Even if there was room to fit ISCG bolts, i would run the cranks as close to the backplate as possible top preserve the chainline.

    Krispy
    Santa Cruz Bronson 2 27.5/Rockshox Pike/Sram XX1
    Salsa Mukluk/Rockshox Bluto/Sram X1

  6. #6
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    Thanks for the help dudes. Sounds like I'm gonna have to just eventually say fuggit and buy the XT's and see for myself. The biggest issue that I've run into in setting up the Race Faces was getting them as far outboard as possible on the drive side to keep the chain from rubbing on the bash ring or the ISCG boomerang. The MRP on there is an ISCG bolted type, but does have bolts with countersunk heads, so hopefully. Thanks again

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