View Full Version : Derailleur chain rub

10-03-2002, 03:14 PM
I just upgraded to Flight Deck STI shifters and a 9-speed cogset. When I'm on the small ring, I get chain rub if I use the smallest three cogs. With downtube shifters, I would get rid of chain rub by manipulating the shifters. How the heck do I get rid of chain rub with STI shifters? I know not to use a little/little chain combination, but I'd rather not give up the other two cogs.

Thanks in advance for the advice!

10-04-2002, 11:13 AM
The small chainring on a triple crankset is only intended to be used with the largest few cogs. Using the small chainring with the <i>smaller</i> cogs is forcing the derailleurs to work at their limits. In addition, the gear ratios from these extreme gear combinations are duplicated by other combinations which use the middle and large chainrings. Bottom line is that the small chainring is only intended to be used for steep climbs, using the 3-4 largest rear cogs. On a shallow climb or flat, use the middle or large chainrings.

10-04-2002, 08:14 PM
I have a double ring crankset. My small ring is a 38T, which gives me more options than the 42T I had, but there's no way I'll be able to climb anything in my big (53T) ring. :(

10-05-2002, 05:21 PM
Ah, I see. Since you don't have a triple, your problem is chain alignment, which can be quite a bit off even on brand new stock-equipped bikes. I had this problem on one of my bikes until I got a new bottom bracket and the bike shop owner who installed it adjusted the chainline with a special guage. With a double crank and a 9-speed cogset, the center cog should be perfectly straight behind the MIDLINE between the two chainwheels. You may have to find a specialty high-end bike shop to do the adjustment, which will probably requires some shims. Once the chain alignment is set up properly you should be able to use all but your smallest cog with your small ring, although in a few cases, if you have unusually short chainstays, you MIGHT not be able to use the second-smallest cog. You definitely will be able to use the third-smallest cog when your bike is set up properly.

10-05-2002, 10:23 PM
Hmmmm - interesting.

The situation may be hopeless. That new Ultrega drivetrain went onto a Trek 460. The rings & cranks were replaced, but there may be only so much room on this frame to 'tweak' things.

If all else fails, I'll just live with the damn squeak and replace the cage way too often. :cool:

10-06-2002, 09:21 AM
Don't give up yet!

It sounds like your bottom bracket (the crank axle assembly) needs to be moved over to the right (moving the crankset outwards) a bit to get the small chainring to line up better with the smaller cogs. Some bottom brackets are adjustable from side to side, and others may be able to accept shims to move them over. Check with your bike shop. If your bottom bracket isn't adjustable, you may be able to get a new, better model that is adjustable. Or, a bottom bracket in a slightly larger (wider) size may do the trick. Bottom brackets do tend to wear out every few years, so you might need a new one soon anyway.

Another thought: if you have a "spoke protector" in between your cassette and your spokes this is unnecessary for a road bike, and removing it might allow your cassette to move inwards a little bit and help with better chain alignment. Just make sure that your rear derailleur limit screws are adjusted correctly after removing the spoke protector.

10-08-2002, 10:21 PM
Thanks for the advice. My LBS isn't exactly local - it's a 100 miles away - but I make the trip relatively frequently.

(There's a LBS 40 miles away, but the guy doesn't inspire confidence in me, so I won't let him work on my bike.)