Bicycle Mechanics - front deralieur rubbing in big ring
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i've got a Surly LHT set up with a tripple in the front and 9 spd in the back. i'm six foot six inches, and ride a 62 cm.
the problem is that when i'm in my two hardest gears (11 and whatever comes next) and my big ring, the chain rubs on the deralieur like crazy. it's cause 1) i'm 6'6" and 2) the tubes are kinda noodlie (because it's a touring frame and is meant to soak up the bumps).
i emailed surly, and they suggested i "gear up" so i'm rarely in the small ring. but i know i'll just get used to the bigger gears and move into them anyway.
so i'm wondering if there's another option. like, say, removing a chainring and moving the crankset inward, or anything else.
the problem is that when i'm up at about 25-30 mph, i want to keep pushing it, but always find that rubbing really annoying.
04-21-06, 06:13 AM
Assuming you've adjusted the limit screw and possibly cable tension, I suppose you could have the incorrect number of spacers which would move the chainline away from / closer to the frame.
Which side of the derailleur is rubbing the chain?
Is it possible that the front shifter was not all the way in the small ring position when the cable was attached? Before attaching the shift cable to the derailleur you need to flip the small shift lever several times while pulling the loose end of the cable. This is to get all of the cable out of the shifter before attaching the cable to the derailleur.
Do you have enough cable tension? There should be no slack in the cable when on the small ring. Adding tension to the cable (counter-clockwise turn of the barrel adjustor) will pull the derailleur more to the right, away from the frame.
Is it possible that the front derailleur is bent or not aligned properly?
04-21-06, 05:19 PM
sounds to me like a simple adjustment problem...
ah the benefits of friction shifters... :D
the front der usually rubs on the right or outside side. it's usually when i'm stomping on the right pedal. i can actually see the chain moving to the right. i do not think it is a BB issue. the BB is set up fine and has been for the past year and a half.
i've had three mechanics — and about ten cycling peers and friends — look at the adjustment and the setup. they tell me it "looks fine." i have a friction, downtube shifter up front. i have brought in all the slack, and i have tightened the adjuster thingie all the way to it's tightest. this happens even when i pull the shifter all the way down.
i do not think the problem is how the bike is set up — i think it's a problem with thinner, more noodlie frames which tend to flex more when taller riders use them.
so with those updates in mind, any other ideas?
04-21-06, 07:59 PM
I can understand frame flex, especially around the bottom bracket shell........even my 52/53cm frames will experience derailleur rub from time to time, especially when I climb out of the sadde to hammer.....in which case I ease out on the outer limit screw which sets the derailleur cage further out. That always eliminates this problem.
You can also spread open the derailleur cage a tiny bit to allow more clearance for this lateral chainring movement...
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