squatchy

My girl frined throws the chain every once in a while. Maybe once every200 miles. She really smart and I have asked her if she does anything unusual and she has said no. I can't make it throw the chain and everything seems good to go. Any thoughts?

BTW Ultegra on a 56 Roubaix pro, and she is a tiny petite rider who doesn't ride rough.

Werkin

The first thing to look at is the gap between FD cage and tallest tooth on the big ring. Set the gap to around 1mm. Next is to adjust the high limit screw if needed.

Tiny petite yet rides a 56?

olds cool

Is it throwing on the upshift or dropping on the down? Either way it can be fixed with the set screws if the derailleur is parallel with the chainrings with the proper distance off the teeth as noted by Werkin.

rpenmanparker 

OP hasn't said GF throws the chain when shifting, just that she throws the chain. First we need to know if during shifting and which direction. If so, obvious fix as stated above is to bring in the limit screw relevant to the direction the chain if falling off. She may jam the lever for the shift to the big ring in a way you don't. If just when riding, she has worse problems than that.

olds cool

Good point there rpenmanparker. I was assuming. I have seen issues on smaller framed bikes having trouble with chain alignment and throwing the chain in the lower gears but the OP mentioned it is a 56. Is the Robaix Pro you have a Fuji? That might be part of the issue. QC is not the best with them.

Cyclelogikal

Is it throwing off the small chain ring or big chain ring? Either way it is likely an maladjusted FD. If it is the smaller of the two you can install a K-Edge chain guard to assist. But I bet her bike just needs adjusting of the FD. How many miles has it been since the last tune?

rpenmanparker 

Another thing OP. You mention the chain unships about once every 200 miles more or less and also you can't get it to happen. But of course, you don't ride it anywhere near 200 miles, right. Maybe around the block to check it out for her. Why would you expect to be able to replicate her experience? This is a statistical and probability issue. All you can do is set up the FD properly and wait for nothing to happen.

squatchy

Hi guys

Thanks for the comments. I do the wrenching on her bike and I keep all our bikes tuned well at all times. She drops the chain off the small ring when shifting down froim the big chainring. The bike is a Specialized. As far as petite, what I mean is she only weighs 145 so she isn't a big girl. I can't see what way to better adjust the stop screws on the front derailure, thats why I'm asking for help. I'll have to look and see if it is too tall away from the teeth when I get there as that is perhaps the problem.

on the path

I've been having the same issue. If the low/high adjustment of the derailler is correct, there are a few other things you can try. Make sure to lube the hinges of the derailler. I think there are six points on mine. Also, you can replace the inner cable and/or the cable housing. I went with the LBS recommendation of oversized cable housing, 5mm as opposed to 4mm. Clean out the groove under the bottom bracket where the cable changes direction. I've done all those things. I'm convinced that I now have the derailler, including cable tension, adjusted properly. Tomorrow will be the test to see if I throw the chain again. If I throw the chain just one more time, I'm getting a chain catcher.

rpenmanparker 

Don't know what you mean by, "I can't see what way to better adjust the stop screws on the front derailure (sic)." Just use the low limit screw to move the derailleur a little bit to the outboard side (away from the frame). Maybe 1/4 turn. You don't have to see the need to do it. That is the obvious fix for the problem. Just accept it. Then check that you don't get too much chain rub on the small front ring and larger rear cog combinations which would tell you that you went too far. Retighten the cable to be taut at this limit screw setting. That should do it.

rpenmanparker 

What makes you think the limit screw adjustments ARE correct? The problem you are having says one of them is not. If you are unshipping to the inboard side when down shifting from the big ring, it means the obvious, the derailleur is allowed to move too far to the inboard side. Move it back away from the frame. You don't have to see the need for the need to be there. The problem says so. Just be sure not to move it so much you get chain rub on the small front/large rear combination or the chain gets stuck between the rings. That's all it will take.

on the path

You quoted me, but I'm not sure who's bike you are talking about. I don't assume the OP's screws are or are not adjusted properly. Mine, I just did more adjusting after today's ride (on which I did not throw a chain in 64 miles). I think it's adjusted properly now.

Not necessarily, not obvious. Even if the limit screws are adjusted properly, the derailler can hang up due to the cable hanging up somewhere along it's travel. If this is the case, the derailler can then snap back at an unplanned and inopportune moment, and the result could be throwing the chain off. My derailler had been hanging up, and I replaced the cable housing and lubed the hinges well, and that's why I made the recommendation to the OP. This is mine final solution, and if it doesn't work, then I'm going with a chain catcher.

RollCNY

On the Path:
in my opinion, all of the things you mention, can be issues, but they are usually issues that bother shifting from small to big, and not cause the big to small shift to over travel.

OP, I would guess if it really is once every 200 miles, and you can't replicate it, that it may be her shifting behavior. And specifically, I would wager on the downshifts that she cross chains big big, and then dumps to the small ring. I have seen this shifting style, especially if done under load, drop a chain to the inside.

Other long shot is if it is a square taper BB, it might be too long, making chainline worse for big to small shifts.

rpenmanparker 

on the path, that is really interesting. I have never seen that happen. I always thought the FD spring was too strong to allow that problem to occur. Nevertheless, what I don't understand is if the limit screw is set right, how can the FD throw the chain off whether there is a delay or not. Basically that is the definition of a properly adjusted limit screw: the FD can't throw the chain off the derailleur. It is all situational.

So just checking: you can't adjust the limit screw a bit to move the derailleur just a little more to the right (outboard side) without causing another problem like not downshifting or too much chain rub when nearly cross-chaining from the small front? Is that right? Because if you can do that without a problem, then your low limit screw is NOT properly adjusted. For sure I can't see whether it is or not. I am just saying that if you can move the FD to the right a little without causing other problems, it is correct to do it. That just may fix the problem. The right adjustment is the one that works to keep the chain on the ring without causing any other issues.

on the path

If I hadn't witnessed it many times, I'd be in agreement. Yes, while on the big ring, I've thrown the small lever (left side) and the derailler didn't move, at least not right away. Would stay there maybe several seconds, 15-20 seconds, a half minute, I never timed it while riding. It happened today actually. I, too, would have thought the spring was strong enough to return the derailler any time the cable tension was released.

Edit: I'll answer the rest of your post this way .. I do believe the lower limit is now exactly as I want it. I get a very slight amount of chain rub when the chain is on the small ring while on the biggest cog in back (lowest gear ratio). That should tell you that the lower limit does not have the derailler too close to the frame. I'm experimenting to see if I lose the chain again. Other than that slight rubbing, which I'll live with, at least for now, there is no other chain rubbing that I can't solve by trimming the front.

bikepro

This can happen if it is cross-chained from the large chain ring and largest cog, or maybe next to the largest cog. Then she shifts to small chain ring. The chain will sometimes miss the small ring and drop. The fix is A. Don't do that. B. Get a chain catcher. Even the TdF bikes have chain catchers these days.

rpenmanparker 

Fair enough as far as that goes. But your criterion for correct low limit screw adjustment COULD be modified to be consistent with the prohibition against cross-chaining. Since most knowledgeable cyclists avoid that small front-largest rear combination as being detrimental to the drive train when ridden for a long time, it doesn't matter if there is rub in that case. You can push to FD even further to the right until just before you get rub on the small front-2nd largest rear combination. Considering how frequently this is the only way to successfully set up a front dearailleur (excluding SRAM Yaw), I have always thought it was the manufacturer's intention that the system would be set up this way.

2 wheeler

I'm confused. The combination that you mention isn't extremely crossed over and yields the lowest gear ratio, which is sometimes very useful. So why do "knowledgeable cyclists" avoid this alignment?

bikepro

He has it backwards. It should be large chain ring/largest cog or small chain ring/smallest cog. While this has been debated ad nauseam, the truth is it happens even with experienced riders. The system must accommodate all combinations, if only for a short time, without failing. The large front/largest rear and a shift to the small chain ring will sometimes cause the chain to drop, even when the FD is properly adjusted. This can happen when descending a hill using the large chain ring. Your start another climb and start dropping gears in the rear. You run out of gears in the back and drop to the small chain ring -- oops, dropped chain in the middle of a climb. The safer method is to drop one or two gears in the rear, drop to the small chain ring and drop or add gears in the rear as needed. I've see TdF riders drop chains like this. A chain catcher is a good way to prevent the problem -- professional riders use em, so do I.

Excelsius

This is a funny coincidence because I didn't find out about exactly what you wrote here until someone in my group ride mentioned it to me today after I dropped my chain. It seems this is why Schleck dropped his chain too few years ago. Once in a while I've been dropping the chain (SRAM Rival) and always thought my LBS didn't do a good job tuning my bike. But it's very likely that my shifting technique hasn't been correct because whenever my chain has dropped, I always remember that I had shifted from the larger chainring to the smaller one while I was using the largest cog. So this could be the cause. I've thought about getting a chain catcher, but if this solves the problem I won't need to get one.

coasting 

limit screw adjust...and then get a chain catcher/dog fang or any of the contraptions that guard against chain drop.

coasting 

i tend to change front gears when in the middle of the rear cogs. When Iget to the last 2 cogs at either end, I get chain rub on the FD and need to use the trim on the shifter. I don't like the rub so I have got into the habit of not going to the extremes at the rear before changing up front.

rpenmanparker 

Correct, on that post I got it backwards. Subsequently I got it right in later posts. The gist was that you can get more protection against dropping the chain on the front shifts if you don't try to keep the "forbidden" cross chain combinations silent. Bring in the FD toward the middle position on both forbidden combinations and let the chain rub on those since you won't be using them for very long anyway. That doesn't cause noise on the allowed combinations and keeps the chain positioned more inside a safe range.