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Old 08-06-10, 01:11 PM   #1
josephjhaney
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Chain drops after conversion *sometimes*

Ok, this is more a vent than anything, but if my chain drops off my crank one more time, I'm gonna scream!!!

I just switched from a triple to a double, now I had my triple setup dialed in as I had it for over 3 years, and didn't change much, but I got the idea to switch to a double as I was rarely using the small ring, and I figured a nice shiny new bike part is always a good thing. I switched the crank, and bb, and left everything else pretty much the same, adjusted it all up, it's still not quite perfect (I have to replace the FD Cable as now i JUST have enough to get it over the fd) but I do have this cable and am planning on doing it this weekend.

My front der is a 105, and rear is dura ace, the 105 however is for a triple. Initially I didn't think this would be an issue, since I could just adjust the limit screws and make sure the cable was in the proper positions, and for the most part it hasn't been, but on a group ride last night I dropped off the top, out over my big ring. I wasn't even shifting the front, I was shifting the rear to the highest gear, and it just hopped off. The only thing I can think is I was pushing pretty hard, and with the new crank and higher tooth count in the big ring, my flex seems to be greater than it was and I think that's what pushed it off the ring.

I found a great deal on a NOS 105 double specific FD on ebay, so I ordered that, even though I don't think that's all, or heck, might not eve be some of the problem, but my current fd does have some wear, and for 25 bucks, ya can't go wrong, so that will be coming next week.

My question is, if it's a frame flex issue, I'm guessing I'm just going to have to tune it as close as I can, then go pound it up a hill in the worst gear and see if it stays on. UGH. Could be a long weekend.

Any suggestions?

Joe
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Old 08-06-10, 01:30 PM   #2
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There's not much to go on so start off by dialing in the trim adjustments. On a double you can use the limits for trim on both rings since there are only an inner and outer. he other thing to consider is that triple front cages are shaped around the chainring combinations typically used, especially the inner plate. You shouldn't have to change, but might find you get better performance out of a double.

Also, next time you buy an inner (used to be middle) chainring, buy one without shift ramps or gates (cut teeth), since you're only shifting up from it, not up to it. No gates reduces chances of derailment.
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Old 08-06-10, 01:44 PM   #3
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There's not much to go on so start off by dialing in the trim adjustments. On a double you can use the limits for trim on both rings since there are only an inner and outer. he other thing to consider is that triple front cages are shaped around the chainring combinations typically used, especially the inner plate. You shouldn't have to change, but might find you get better performance out of a double.

Also, next time you buy an inner (used to be middle) chainring, buy one without shift ramps or gates (cut teeth), since you're only shifting up from it, not up to it. No gates reduces chances of derailment.
The whole double crank is new, so there aren't any ramps. I would agree that the triple is less suited to the shifting than the double will be, that's part of the reason I ordered it. (That and it's a SHINY new part, and it's been a while since I upgraded on this bike, so it's time).

Thanks for the advice, I'll try to dial it in a little more this weekend, but just enough to keep me spinning till my new der comes next week, then I'll have to do it all over again. But, I think that will be the real fix, put the right parts on and get it tuned it, and I think it will be fine then.

Joe
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Old 08-06-10, 01:48 PM   #4
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I dropped off the top, out over my big ring.
Do you mean it went off the outer chainring, away from the bike?

How's your high limit screw adjustment? While in the highest gear (outer chainring and smallest cog), the outer cage should be as close to the chain as possible without causing it to rub.

Also, how high up did you mount the FD? I'm not near my road bike, but I'm trying to visualize if the FD, which is mounted low and barely clears the teeth of the outer chainring, could even allow the chain to get up over the teeth.
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Old 08-06-10, 01:51 PM   #5
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Do you mean it went off the outer chainring, away from the bike?

How's your high limit screw adjustment? While in the highest gear (outer chainring and smallest cog), the outer cage should be as close to the chain as possible without causing it to rub.

Also, how high up did you mount the FD? I'm not near my road bike, but I'm trying to visualize if the FD, which is mounted low and barely clears the teeth of the outer chainring, could even allow the chain to get up over the teeth.
You know thinking back, I think that's part of the issue, I didn't give it much thought at the time, but the cable being too close resulted in me focusing on the inner and not having it rub, I honestly didn't give a lot of thought to the outer limit. I did adjust it, but only to where it was close to the chain.

The height is very very close to the teeth, so that's not it, but I do think I need to replace that cable, and then run that outer limit screw down so it's a lot closer to the chain.

At least it will be good practice for when I do the FD replacement next week.

Joe
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Old 08-06-10, 02:12 PM   #6
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I have had specific triple FD cages cause this on my compact double. The way the cage was formed (both inner and outer plates) allows it to, in just the right instance of power and flex, kick the chain out and off the big ring. At the time I also tried a middle 39 instead of a middle 42 and the cage design didn't allow the chain to shift down to the 30 from the 39. The 42 didn't have this problem. I just ordered a compact FD and haven't had a problem yet.
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Old 08-12-10, 06:58 AM   #7
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Ordered the 105 double, even ended up getting the 10 Speed version, put it on and adjusted last night, I think that was it. The combination of the "thicker" plates on the triple shifter, along with the wider tolerance was allowing my double to drop off the front, the deeper plate was much more effected by the flex of pedaling in the 53 than is the thinner inside or "upshift" part of the FD. I think I've got it dialed in just about perfect, and I only get rub in the very top gear, which I can trim out withe the shifter. Very sweet setup now. Thanks all for the advice, now I just have to get used to pushing that 39/25 combo up these hills, and see if my knees can adjust.

Joe
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