I ride a Specialized Roubaix Expert, with FSA compact cranks and Ultegra components. I have chain rub that can't be removed by setting the limit screws or rotating the front derailleur. My bike shop wants to bend the front derailleur cage, but I have resisted letting them do that. Should I agree to it?
Bending Front Derailleur Cage
Fri, 09/29/2006 - 5:55am
Fri, 09/29/2006 - 6:06am
#1
I assume you're talking about chain rub outside of the cross-chained gear combinations (e.g., I don't use my 2 smallest cogs when in the small chainring and don't use my 2 largest cogs when in the big chainring).
Is the FD cage straight or is it warped? If it is straight, it seems to me that height and rotational adjustments should solve the problem.
When you're making limit screw adjustments, the FD wire is completely slack, right?
Fri, 09/29/2006 - 6:31am
#2
Bending Front Derailleur Cage
"The chain rub occurs in the small-large and large-small combinations-- i.e., not when I am cross-chaining. And more importantly, it occurs when I am using combinations that can't be reproduced by using the other chainring. I can't solve the problem by changing the limit screw settings, because doing so causes the chain to fall off. (I have encountered other people with FSA compact cranks that experience the chain falling off.)
Regarding your other questions, the FD cage is straight, not warped. And when I make the limit screw adjustments, I take most of the tension out of the FD wire."
Fri, 09/29/2006 - 7:09am
#3
Maybe a silly question, but are you using a front derailleur made for a compact (or triple) crank? It's well established that regular Shimano FD's don't work well with compact cranks.
Rather than bend your old one (I'd say a 50/50 chance at best), just put it up on eBay and get a compact FD.
Fri, 09/29/2006 - 7:49am
#4
Bending Front Derailleur
It wasn't a silly question. I'm using an Shimano Ultegra front derailleur. I didn't know that Shimano derailleurs didn't work well with compact cranks. Another compact crank user in the club sent me an e-mail saying that he solved his derailment problem by getting the FSA derailleur. So you may be right that that is the solution.
Fri, 09/29/2006 - 7:58am
#5
disagree
"I'm using DuraAce standard double front derailers on two bikes with compacts - 33x48 and 34x46 - without problems. Before the term ""compact crank"" was coined there were no ""compact front derailers,"" only touring cranks and double or triple FDs, so you used what was available. It worked fine then and it still does now.
I'd be genuinely interested to see where it has been established that regular Shimano FDs don't work well with compact cranks and what exactly the problems are. My observation is that compact FDs are the answer to a question that hasn't been asked (aka marketing BS) but I'm willing to be proven wrong."
Fri, 09/29/2006 - 8:38am
#6
"Maybe ""well established"" is strong wording, but I've personally spoken to at least a half-dozen folks who've changed to compact systems and had problems with ""normal"" Shimano FDs. I've also worked with one on a stand and could never get it just right. On the other hand, Campy FDs seem to have a greater capacity than their stated rating, and many people (myself included) have successfully used non-compact Campy FDs on compacts.
The two cranks you describe on your bikes, by the way, are somewhat unusual in that the tooth-difference between the two chainrings is slightly less than that of the most-common compact set up, namely, 50/34. Your 48/33 requires an FD with a 15-tooth capacity, whereas most compacts need an FD with a 16-tooth capacity. I realize the one-tooth difference shouldn't really matter, but maybe it's the difference between acceptable and unaccceptable performance. Or maybe the difference is DA vs Ultegra."
Fri, 09/29/2006 - 9:07am
#7
What exactly are the problems?
What is it that doesn't work right? Inability to shift, throwing the chain to the inside, what?
Fri, 09/29/2006 - 9:26am
#8
Most noticeable is a slow lift from the 34 to the 50. My 50-36 shifts noticeably better than my 50-34, and I think DvB is on the right track that it's the tooth difference that is the biggest culprit.
Fri, 09/29/2006 - 7:55am
#9
I'm using an FSA compact crank with an Ultegra 6600 derailleur. It took a little adjusting but I have no chain rub in straight-chain combos and the chain does not get thrown to the inside or outside.
You will need to lower the FD a little, but don't let it get as close to the large chainring as you would on a 52t or 53t chainring - so instead of 1mm of clearance, give it 3mm of clearance.
Take all of the tension out of the FD wire - make it really slack - pull on the wire with your hand to effect shifting while adjusting the limit screws. If you haven't already read it, the Park Tools site has an excellent guide on adjusting the FD. Take heart - it can be done w/o bending the FD cage, replacing the FD, or using ThirdEye chain catchers.
Fri, 09/29/2006 - 7:03am
#10
Sometimes you can get rid of the rub by loosening the cable adjuster slightly - it might be on your downtube or headtube depending on the frame.
Sometimes you just have to go ahead and bend it. No big deal really, if it's done carefully the rub goes away and the shifting doesn't change at all.
Fri, 09/29/2006 - 7:07am
#11
When you bought the bike, was the compact already installed? If not you will have to lower the FD.
From FSA's faq:
I want to buy compact cranks. What do I need to do to set this up on my new bike?
You’ll need to lower the front derailleur by 10 mm and readjust the shifting. It’s also recommended to shorten the chain so you’ll have less chain slack with the smaller gearing. Otherwise, if you’re currently running a road double, there’s nothing new you’ll need to buy.
I am having trouble adjusting shifting on my compact cranks.
While a standard road front derailleur is designed around the 53/39 gear combination, we’ve had plenty of luck using Campagnolo or Shimano front derailleurs on compact setups. One suggestion that works for us is: instead of running the derailleur as close to the rings as possible, raise it up by a millimeter or two. This makes the gear change happen not quite as abruptly and reduces the chance of the chain derailing to the inside.
You can also try this little gizmo
Fri, 09/29/2006 - 7:52am
#12
Bending Front Derailleur Cage
Yes, the compact cranks are standard on the Roubaix Expert. Also, my shop lowered the front derailluer several millimeters in an attempt to address the derailment problem. So derailleur height doesn't appear to be the source of the derailment and chain rub problem.
Fri, 09/29/2006 - 9:53am
#13
Yes
I use a FSA compact crankset with Campy Record. Campy compact front derailleurs are notorius for not working that well when shifting to the big ring. Lots of chatter before engaging. Can be the result of a number of combination factors. I played around with it's adjustment and finally bent the cage to address the shifting issue. Works damn well now.
