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FD Chain Rubbing!(4 posts)

FD Chain Rubbing!Xoc
Apr 20, 2003 4:58 AM
Hey All,

I recently picked up a used TCR built up with 8 speed ultegra/600 parts.

I'm new to the road biking world, but I've been an MTBer for a good number of years and have built a few bikes from the frame up.

My road bike has a double up front, and I've got the low and high limits as far out as they will go, but I still get major rubbing in both chainrings when the gears are crossed. Is this type of rubbing normal for a double on a road bike, or do I have some sort of mech problem? I've always been able to get a MTB shifting great with no rubbing at all.

The shifting works great, just rubs. It's almost like the front mech just doesn't have enough travel, as it's a matter of milimeters for it not to rub, it's a braze on mount, so I can't tilt the derailer at all easily.

I think I'm going to replace the entire group with Ultegra or Dura Ace in the near future, but this stuff works pretty well other than the rubbing.

Any suggestions?
may be normal...C-40
Apr 20, 2003 5:30 AM
First rule of road bike drivetrains. Never use the two extreme chainring-cog combos (big chainring-largest cog or little chainring and smallest cog). Some bikes will also have minor rub in the small chainring and the next to smallest cog.

It's odd that you have the limit screws all the way out and have not thrown the chain off in both directions. Most FDs have enough travel to do this, unless the screws are set in by some amount.

Be sure that you have the correct bottom bracket spindle length for your crankset.

Also be sure that you understand how to adjust the cable tension on a front derailleur. If the cable is slack when the derailleur is in the little ring, then the tension is incorrect. Increase until there is no slack in the cable when the derailleur is in the little ring. Otherwise, when you shift to the big ring, you will not get the full travel of the derailleur.

Also be sure that the dearilleur cage is parallel to the big ring and set at the proper height. There is normallly only 3-4mm or a little over 1/8" clearance between the teeth on the large chainring and the derailleur cage as it passes over the large chainring. If these adjustments are not correct, then the derailleur will not function properly.

Check out the parktools.com website. They usually have good instructions for most basic bike adjustments.
Check cable tensionB2
Apr 20, 2003 7:53 AM
I think C40 is right to recommend checking the cable tension. If it's not tight enough, you won't get the full range (on the big ring) no matter where your stop is set.

Also, if you find that it's all adjusted correctly and you're still getting rub in the 2nd or 3rd extreme combos, try inserting a 1mm washer to spread the front derailleur at the location shown in the picture. It's not ideal, but this can help pick up one more cog before the rubbing begins.

Good Luck,
Bryan
There are some other things you can checkLive Steam
Apr 21, 2003 4:02 PM
First check to see that the front der. is aligned properly with the chain rings. The front der. on your TCR is mounted as a braise-on (sic) and can toe in or out for fine tuning. If it is toed in, the back of the cage will rub an a few combinations. The cage should be parallel to the rings. Also check the height above the rings. The cage should be no more than 1/4 inch above the rings. If it is too high the chain will also rub when in certain combinations. The last thing to look at is the BB. What length is it? Too long or too short can cause poor chain alignment. An improperly installed BB will have the same effect.