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  1. #1
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    Chain rubbing inside of outer chainring

    I have a Strongligth Pulsion 50/34 compact crankset with a 108mm Token ISIS BB. When I am in the outer 3 cogs in the rear, the chain rubs against the inner surface of the big ring. I have put a 1mm spacer to offset the crank 1mm to the drive side and this made it only very slightly rub on the 3rd cog. I have had this problem for a while and was wondering what is the best solution:

    1) try a 36 chainring. I am sure this helps since it will move the point the chain leaves the inner wring up by a about 4mm, but I am not sure how much of a difference it will make.

    2) go from a 108 BB with a 1mm spacer on the right to a 113BB with no spacer This will move the chainline out another 1.5 mm. If it is just rubbing at the 3rd cog, and the 2nd cog is 4mm further out from the bike than the 3rd, then the chainrings would have to move out 4mm for the chain to only be slightly rubbing for the 2nd cog. So I don't think it would help that much, but could make things worse for the bigger cogs when in the big ring

    3) put spacers in for the big ring so that there is a larger space between the big and small ring. I think this would work best, but not sure it is a good idea on the Pulsion. The fairly small carbon tabs that are sandwiched between the two rings might not be made to have the force all on a small area (where the spacer is). Right now the chainring surface is flat against the entire tab.

    thanks for any suggestions.

  2. #2
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    If you were to put a spacer between the chainring and the spider, you'd likely create too much space between the chainrings, and your chain could jam between the rings. Is your entire drivetrain 10 speed specific? Many aftermarket cranks are for 9 or 10 speed. 9 speed chains are a bit wider than 10 speed, so perhaps if you are running 9 speed, you may have to switch to 10 speed for optimum results. There are a lot of variable that could cause your problem, but I'd start with the chain, and make sure it is the correct width.

  3. #3
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    Good point. I have a 9 speed cassette with a 9 speed chain. However the crank is for 9 or 10 speed.

  4. #4
    duh...
    Reputation: FatTireFred's Avatar
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    that happens when you crosschain, common issue. and as you've surmised, messing w/ chainline/bb spindle length presents other issues
    .


    Quote Originally Posted by mikagsd
    Fat tire Fred....you are the bike god of the universe and unless someone agrees with your reasoning they are just plain stupid

  5. #5
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    That isn't always true. I had an Ultegra 53/39 and it didn't do it even when running small ring and small cog (not that I did this while riding, this was in the stand). I don't really consider small ring and 3rd cog as crosschain anyway. But the biggest reason I don't like what is happening is that I am sure that if I screw up and do go to small ring and cog 1 or 2, then I just want some noise and excessive wear to happen, I don't want the chain to get caught by the shift pins/ramps and pulled and up jammed, and possibly have things broken.

  6. #6
    Probably slower than you.
    Reputation: suprcivic's Avatar
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    personally, i like to tinker. i would try the longer BB and see if it works. buy it at performance or REI. that way, if you have chainline issues, you can return it.

    i've had that issue before. fortunately, i had an external BB with spacers on the non-drive side, so all i had to do is switch the spacers over to the drive side. it fixed it and i had no chainline issues.

    definitely don't put spacers on the big chainring.

  7. #7
    duh...
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    Quote Originally Posted by lemmy999
    That isn't always true. I had an Ultegra 53/39 and it didn't do it even when running small ring and small cog (not that I did this while riding, this was in the stand). I don't really consider small ring and 3rd cog as crosschain anyway. But the biggest reason I don't like what is happening is that I am sure that if I screw up and do go to small ring and cog 1 or 2, then I just want some noise and excessive wear to happen, I don't want the chain to get caught by the shift pins/ramps and pulled and up jammed, and possibly have things broken.


    common issue WITH COMPACT CRANKS
    .


    Quote Originally Posted by mikagsd
    Fat tire Fred....you are the bike god of the universe and unless someone agrees with your reasoning they are just plain stupid

  8. #8
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    I have always heard this is an issue with compacts as well. However I don't really understand why. If you measure the distance from where the chain takes off from the inner ring to the point where the chain clears the edge of the outer ring, you will find that a 53/39 is a longer distance (and should be worse) than a 50/34 or a 50/36.

    http://www.ssfweb.info/chainring.pdf

  9. #9
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    Quote Originally Posted by cyclust
    If you were to put a spacer between the chainring and the spider, you'd likely create too much space between the chainrings, and your chain could jam between the rings.
    Depends on the crank set.

    My FSA compact rubbed with my Campagnolo 9-speed setup.

    I found that the chain rings on my FSA compact were closer than Campagnolo specified for their 10-speed cranks which are .4mm tighter than 9 speed cranks.

    Adding .4mm got me a couple cogs with no effect on shifting; 1.0mm made everything usable but shifted slower; I don't recall if I left that or went to .8mm.

  10. #10
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    Quote Originally Posted by lemmy999
    Good point. I have a 9 speed cassette with a 9 speed chain. However the crank is for 9 or 10 speed.
    Several companies (Wheels Manufacturing, LeTour) sell .6mm spacers specifically for making 10-speed cranks work with 9-speed chains and cogs.
    Last edited by Drew Eckhardt; 04-14-2010 at 12:55 PM.

  11. #11
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    So you were using spacers to adjust the spacing between your inner and outer chainrings? I don't know if I can do that on the crankset I have. Also, I have read that the spacing on the Stronglight Pulsion is a little more than it is for the Shimano. The only reason I can figure that I have having this rubbing is that possibly the Stronglight chainrings are a little thicker in the body (not where the teeth are).

  12. #12
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    Quote Originally Posted by lemmy999
    So you were using spacers to adjust the spacing between your inner and outer chainrings?
    Yup.

    I don't know if I can do that on the crankset I have.
    Sure you can. The spacers go around the chain ring bolts and either move the outer ring out or inner ring in.

    Also, I have read that the spacing on the Stronglight Pulsion is a little more than it is for the Shimano. The only reason I can figure that I have having this rubbing is that possibly the Stronglight chainrings are a little thicker in the body (not where the teeth are).
    Measure the thickness of the crank spider where it mates to the rings and chain rings with your calipers (if you don't yet have a pair, places like harbor freight have inexpensive dial calipers). Add the spider thickness to half of each chain ring's thickness and compare the total to published "standard" numbers.

    Or compare the spider thickness where it meets the rings with your old crank.
    Last edited by Drew Eckhardt; 04-14-2010 at 12:55 PM.

  13. #13
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    Thanks.

    I understand how the spacers work, I am just not sure it is ok to use with the carbon spider on my crank. Right now the flat tabs on the spider are sandwiched between moderate sized flat sections on both chainrings. It seems that if I put a spacer in there, all forces would be concentrated on a much smaller area on the carbon tab on the spider. Maybe it wouldn't matter though...not sure.

  14. #14
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    It is a common problem with compact cranks, and made worse if you have short chain stays.

    Unless you are using a 10sp crank with a 8 or 9sp chain/cassette, I would not put spacers between the chain rings. Spacing out the chain rings will cause the chain to shift between the chain rings, and can also cause false neutrals.

  15. #15
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    I can understand short chain stays causing this problem, but even though I admit I hear of more people with compacts having this problem, it just doesn't make sense. Compacts should have less of a problem with it since there is a shorter distance between the chain leaivng the middle ring clearing the big ring.

  16. #16
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    Compacts per-se are not as much the problem as the size difference (or ratio) between that of the big and small chain rings. The ratio is usually greater between the large/small rings of compact cranks than it is with standard cranks.

    Your 50T/36T compact would be equicvelent to running a 53T/36T current standard size crank (smaller ring being 3T smaller than the normal 39T). A 53T/36T standard crank would have rubbing issues too.

    If you are set on keeping your 50T, you should be able to eliminate your rubbing by changing your inner ring to a 37T or larger, which would result in a similar ratio as a stock 53T/39T standard cranks, but still a larger ratio than the older stock 52T/42T standard cranks.

  17. #17
    duh...
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    Quote Originally Posted by RHankey
    Your 50T/36T compact would be equicvelent to running a 53T/36T current standard size crank (smaller ring being 3T smaller than the normal 39T).


    huh?
    .
    .


    Quote Originally Posted by mikagsd
    Fat tire Fred....you are the bike god of the universe and unless someone agrees with your reasoning they are just plain stupid

  18. #18
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    Quote Originally Posted by FatTireFred
    huh?
    .
    Oops. Meant to write that a 50T/36T is equivelent to a 53T/38T (1T smaller ring than a current standard crank).

    As I previously wrote, the OP should be able to eliminate rubbing with a 37T or larger small ring.

    Thanks for catching that error.

  19. #19
    duh...
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    Quote Originally Posted by RHankey
    Oops. Meant to write that a 50T/36T is equivelent to a 53T/38T (1T smaller ring than a current standard crank).

    As I previously wrote, the OP should be able to eliminate rubbing with a 37T or larger small ring.

    Thanks for catching that error.


    who makes a 37t x 5 bolt x 110bcd chainring?
    .


    Quote Originally Posted by mikagsd
    Fat tire Fred....you are the bike god of the universe and unless someone agrees with your reasoning they are just plain stupid

  20. #20
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    Quote Originally Posted by lemmy999
    Thanks.

    I understand how the spacers work, I am just not sure it is ok to use with the carbon spider on my crank. Right now the flat tabs on the spider are sandwiched between moderate sized flat sections on both chainrings. It seems that if I put a spacer in there, all forces would be concentrated on a much smaller area on the carbon tab on the spider. Maybe it wouldn't matter though...not sure.
    I've had the spacers on my FSA Carbon Pro Compact (the first one, with the separate carbon fiber spider) ISIS cranks for seven years without issue. That's a data point, not necessarily an endorsement.

    If you were really worried you could just trim some shim stock down to size with tin snips and preserve the contact area.
    Last edited by Drew Eckhardt; 04-15-2010 at 08:05 AM.

  21. #21
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    Quote Originally Posted by Drew Eckhardt
    I've had the spacers on my FSA Carbon Pro Compact (the first one, with the separate carbon fiber spider) ISIS cranks for seven years without issue. That's a data point, not necessarily an endorsement.

    If you were really worried you could just trim some shim stock down to size with tin snips and preserve the contact area.

    I have heard the spacing is usually around 5mm for between rings. I measured mine as best as I could and it seems that the spider tab thickness is 3.5mm. The outer ring is around 3.6mm and the inner ring around 3.3mm. So that would be a spacing of around 7mm. The actual gap between the chainrings is 3.5mm and so I guess I could put a 0.6mm spacer for the large chainring and the 10sp chain (5.88mm wide) would still should not be able to wedge down between.

    Stronglight claims that a 108BB with this crankset should give 43.5mm chainline. I have a spacer on the right side (1mm) so I should have a 44.5mm chainline. However the total thickness of both chainrings and the spider is ~10.5mm. I measured from the middle of the seat tube to the outside of the chainring and it was 46.25mm. If I then subtract 10.5/2 to get to the middle of the rings, that would put my chainline extremely low at ~41mm. I am sure I could be off 1mm. But that still leaves me way under the recommended 43.5. I measured the rear and it is around 42.2m (130/2 - 22.8). This is making me wonder if I shouldn't try the 113mm BB. Maybe this problem could be caused by the BB not really being as wide as it claims..or possibly it allows the crank to go up on the spindle more than it should.
    Last edited by lemmy999; 04-15-2010 at 09:43 PM.

  22. #22
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    Quote Originally Posted by lemmy999
    I have heard the spacing is usually around 5mm for between rings. I measured mine as best as I could and it seems that the spider tab thickness is 3.5mm. The outer ring is around 3.6mm and the inner ring around 3.3mm. So that would be a spacing of around 7mm. The actual gap between the chainrings is 3.5mm and so I guess I could put a 0.6mm spacer for the large chainring and the 10sp chain (5.88mm wide) would still should not be able to wedge down between.

    Stronglight claims that a 108BB with this crankset should give 43.5mm chainline. I have a spacer on the right side (1mm) so I should have a 44.5mm chainline. However the total thickness of both chainrings and the spider is ~10.5mm. I measured from the middle of the seat tube to the outside of the chainring and it was 46.25mm. If I then subtract 10.5/2 to get to the middle of the rings, that would put my chainline extremely low at ~41mm. I am sure I could be off 1mm. But that still leaves me way under the recommended 43.5. I measured the rear and it is around 42.2m (130/2 - 22.8). This is making me wonder if I shouldn't try the 113mm BB. Maybe this problem could be caused by the BB not really being as wide as it claims..or possibly it allows the crank to go up on the spindle more than it should.
    Having the chain get wedged between the chain rings is only one risk if the chain ring spacing is too great. The other problem is when the spacing is wider than it should be but not wide enough to jamb the chain, in which case one side of chain plates will ride on the top of the inner chain ring teeth. This latter issue is what causes very annoying false neutrals.

    In short, if all the driveline components are correctly matched, then you do not want to be adding spacers beween the chainrings. Spacers are only really a viable option if using lets say a 10sp crank with an 8sp chain and drivetrain.

  23. #23
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    Quote Originally Posted by FatTireFred
    who makes a 37t x 5 bolt x 110bcd chainring?
    TA makes one. You can get it from Harris.

  24. #24
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    Quote Originally Posted by RHankey
    In short, if all the driveline components are correctly matched, then you do not want to be adding spacers beween the chainrings. Spacers are only really a viable option if using lets say a 10sp crank with an 8sp chain and drivetrain.
    Contemporary 10 speed compatible cranks aren't correctly matched to 9 speed drive trains like lemmy999's.

    For example:

    Campagnolo 9 speed chains are 6.8mm wide. Campagnolo 10 speed chains were initially 6.1mm wide and have shrunk to 5.9mm. The chain rings need to be .35 - .45mm closer for the same clearances, and Campagnolo machined .4mm off the back side of their 10 speed outer rings.

    .4mm restores stock spacing.

    Photos at Branford Bike:
    http://branfordbike.com/articles/chainrings-pg68.htm

    Some cranksets have even less clearance between the "9 and 10 speed compatible" rings than Campagnolo.
    Last edited by Drew Eckhardt; 04-07-2012 at 12:31 PM.

  25. #25
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    Before adding spacers, etc., have you actually checked the chainline? Also, have you checked frame alignment? Might be a good idea to know what problem you're trying to fix.

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