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  1. #1
    Prairie Path Commuter
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    How much distance between inner chainring and chainstay?

    I just installed a Nashbar Trekking Crank onto my MTB (triple 110 mm BCD). After I got done I noticed that I only had about 1-1.3 mm of clearance between the tip of the inner chainring teeth and the chainstay. Although the chainstay approaches at an angle so that only the tip of the teeth come close. I also measured the front chain line at 45.5 mm and the rear chain line at 43.7 mm with a calipers using the method in Leonard Zinn's book. This chain line seems good to me. The BB is a 68 x 113 mm FSA Platinum Pro and the spec for the crank was to use a 113 BB with 1 1/8 inch tubing, which I have. Also, the clearance of the tip of the non-drive side crank is only 5 mm (10 mm on the drive side).

    Assuming that there are no other problems here are the options that I am contemplating.

    1. Run it as is. Hopefully 1 mm is enough.

    2. I just read a method to adjust the FSA Platinum Pro BB. Apparently there is no lip so spacers can not be used but the entire BB can be shifted left or right. I could give up 1 mm on the non drive side but that would only leave me with 4 mm between the crank and the chainstay.

    3. Get a larger BB. The spec for the crank says only to use a 113 or a 118 mm BB but I suppose I could get something like 116mm, which would give me an extra 1.5 mm on each side. This will however make my chain line worse but probably not terrible.

  2. #2
    Klaatu barada nikto cascade168's Avatar
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    Yeh, that's pretty tight, but ...... that clearance usually is on most bikes. You will see a lot of bikes where the drive side chainstay is dimpled or bent in an "S" to give more clearance to the granny ring. I'd say that as long as there is not too much flex in the frame, or crank, or BB, or whatever, and there is no contact between the chainstay and the chainring, then you are ok. The only way you are going to find this out is to get out and ride and do a little hammering. I would give it a shot, myself. If you get some contact then you are going to have to space it further out.

    The 5mm clearance you talk about on the left side is pretty common. If you take a look down when you are riding (careful here!), you will see that the inside of your heels are just barely missing the crank arms. Almost all of my shoes have scuffs because of this. There are lots of tight clearances between the rider and the drivetrain, and, the drivetrain itself has plenty of tight clearances. Good luck with your ride ;-)
    "Work is the curse of the drinking class."
    - Oscar Wilde

  3. #3
    Senior Member
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    The industry standard for chainring and crank arm clearance to the frame is 2mm. Just shift the b.b. over a little bit.

  4. #4
    Sometimes knows stuff. rmfnla's Avatar
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    What you want is both pedals to be the same distance from the centerline of the bike and for nothing to rub.
    Today, I believe my jurisdiction ends here...

  5. #5
    me have long head tube TallRider's Avatar
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    Thanks for offering good detail in your question. Now, as long as your bike's frame, BB and drive-side crankarm are stiff enough, things should be fine with 1mm of clearance. If it's not - and this will be apparent quickly - you can shift it over 1mm, which won't appreciably affect the chainline.

  6. #6
    Senior Member DannoXYZ's Avatar
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    sounds like you need a 118mm BB spindle so that both cranks/pedals are spaced evenly apart... keep the right side exactly as it is, move the left side outwards to match...

  7. #7
    Senior Member
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    If you have the regular platinum pro, you will need to use spacers. The track platinum pro is made for adjustable chainlines. You might try spacing the cassette to help with the chainline.

  8. #8
    Prairie Path Commuter
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    Quote Originally Posted by CBolt
    If you have the regular platinum pro, you will need to use spacers. The track platinum pro is made for adjustable chainlines. You might try spacing the cassette to help with the chainline.
    Good point. I saw that when I went back and looked at it again the second time last night and was wondering what the poster in thread I was reading was talking about. There obviouly was a lip on the BB and it was flush up against the frame. This kind of reduces the appeal of getting a 118 mm BB because I won't be able to feed back some of the extra 2.5 mm I would gain to the nondrive side to increase and even out the distance between the cranks and chain stay.

    I remeasured the distances between the cranks and chainstays this morning a little more carefully. This time I got 5.5 mm on the nondriveside and 8 mm on the driveside. Not perfect but not too bad I thought, although I am not thrilled with having the cranks that close to the chainstay and hope that my heals do not rub.

    I can not get a calipers to the point where the inner chainring and chainstay come close but I looked at it again this morning and concluded that it is more than 1 mm, probably closer to 1.5mm.

    Because the chainline is good now, I think I am going to run it as is. Plan B would be to put a 0.5mm BB spacer on the driveside. Plan C would be to go with the 118 mm BB but I am also afraid that the incease in front chainline will have a negative effect on shifting.

    Thanks everybody for the responses.

  9. #9
    feros ferio John E's Avatar
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    Try riding it for awhile. If it doesn't rub, don't worry about it. With a Campag. Veloce triple and a cartridge BB, I have at most 1mm of clearance on my 1959 Capo; countersinking the bolt holes on the inner ring eliminated any tendency to rub.
    "Early to bed, early to rise. Work like hell, and advertise." -- George Stahlman
    Capo [dschaw'-poe]: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger, S/N 42624
    Peugeot: 1970 UO-8, S/N 0010468
    Bianchi: 1981 Campione d'Italia, S/N 1.M9914
    Schwinn: 1988 Project KOM-10, S/N F804069

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