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Rubbing Chainrings(11 posts)

Rubbing Chainringsbuffedupboy
Apr 14, 2003 6:43 PM
Hello all gurus of Bicycle world,

I have a problem that I hope some of you can solve. I ride a Schwinn Fastback '99. It is equipped with an Ultegra 9 speed/ Double Crankset.

The problem is when I am in the smaller chainring and the second smallest/ smallest cog, the chain rubs on the inner face of the larger chainring.

I was told by a LBS that I should swap my BB-6500 with a 109.5mm spindle length for a MTB BB like an XT BB-ES70 with a spindle length of 113mm. This I was told would push my crankset away from the BB shell thus pushing the chainline further away. I was wondering whether there are any other problems that can come from this. Was also wondering whether it would be a better idea to use a triple crankset BB with a spindle length of 118.5mm instead. Any incompatibility issue with the MTB BB?

All suggestions and advice is greatly appreciated.

Or, shim BB with a 1.5mm washer. Don't use small-small. nmSpunout
Apr 15, 2003 5:00 AM
It's the most elegant fix. I did it,OldEdScott
Apr 15, 2003 7:44 AM
and have had no problems. If you don't want the expense, a spacer or two will do the trick until the time comes for a new BB.

This is a tremendously common problem.
my problem too! what type of shim/washer to use?rockbender
Apr 15, 2003 8:47 AM
What is the best shim solution here? Find another BB lockring to screw on? I also considered putting some small washers behind the small ring to get it spaced out a bit, but that wouldn't help the chainline (though the difference would be very small).

I went from a triple BB/crankset to a double BB/crank (both ultegra. The bike came with the triple... Does the specific BB (double or triple) place its matching big ring in the same position?

my problem too! what type of shim/washer to use?OldEdScott
Apr 15, 2003 10:46 AM
A 2mm spacer behind the drive side cup will increase chainline and alleviate the problem. QBP lists these spacers in their catalog so any shop should be able to order one for you. Hell, Trek is so aware of the problem they have some nifty double-secret spacers they'll give you if you complain about it.
cool. Thanks! (nm)rockbender
Apr 15, 2003 10:55 AM
Normal, not a 'Problem'cyclequip
Apr 16, 2003 12:06 AM
It has to do with the length of the chainstays on some compact frames. Rather than throw off the chainline by installing the wrong length axle, leave it and don't cross up your chain.
re: Rubbing Chainringswielerpret
Apr 16, 2003 3:30 AM
Considering the chain alignment, it is not very wise to use the 2 smallest cogs with the small frontblade in the first place. Chain as well as cogs will wear a good deal faster and are likely to sound less smooth. What about the large frontblade with the fourth largest cog? It is what I experience early in the season when I am not yet strong enough to use the large frontblade with headwind. I never use the combination of large frontblade with second or third largest cog either for that matter. However, I am blessed with a 10 speed gear and single sprocket intervals...
If you use the combination you mentioned often and the one I am suggesting is too heavy, you may consider mounting another cassette altogether. Good luck. Luke. Amsterdam.
re: Rubbing Chainringsbuffedupboy
Apr 16, 2003 9:20 AM
Thanks everyone for all your advice. I still haven't decided what I will be doing.

I ride with the smallest chainrings at the start of my rides so that I can spin more, then I up it to my larger chainring and just crunch away for the rest of it.

I have a secondhand MTB BB so I may just try that if the LBS does not have the shim/ washer suggested.

Thanks again,
re: Be careful of what MTB BB you tryMike Prince
Apr 18, 2003 7:41 AM
As far as I can remember, only the XTR spline pattern is compatible with Shimano road cranks. I did on my bike exactly what you want to do, using a XTR (952) BB with a 112.5 mm spindle to increase the chainline with a D/A crankset. The XT/LX-level BB's will not work with the road cranks and that is what I believe the ES-70 BB is. The XTR solution works like a charm (and is 40+ gm lighter than the Ultegra BB), but the spacer approach should work equally as well. I had the advantage of this happening when I was building the bike up, so I just swapped BB's out at minimal ($10) cost.

If I was you, I'd try the $1.00 spacer first before shelling out $40+ for a new BB. Be warned you may still get some rubbing in the small/small combo, but as others have said, you really shouldn't be using those gears anyway (or the large/large combo).

re: Be careful of what MTB BB you trybuffedupboy
Apr 18, 2003 8:40 PM

I am unable to locate a spacer for the BB. I have looked at the BB and the cranks and can't even figure out where the spaver should go. This is because if I put in a spacer before the splines, then the cranks won't lock onto the BB. If I put the spacer after the splines, then the spacers will not be able to mount onto anything, hence rendering them useless. Kindly advice.