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Old 01-18-11, 09:33 PM   #1
TrekmanDan
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What to consider when upgrading derailleur?

My wife and I went out for a ride a couple weekends ago at Terry Hershey park and halfway through, I was downshifting from my big ring to my small ring and my chain fell off! I've adjusted the Limit screws several times, but it still doesn't perform like I want it to. Keep in mind, I have low end components... Sora in the front and Tiagra in the back - which is probably part of the problem. I really want to replace my front derailleur and was wondering what I need to look for when doing so. I believe i need a clamp on, but aside from that is there anything else that I need to look for when buying one? Also, do I need to change anything else when upgrading?
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Old 01-18-11, 09:54 PM   #2
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1. The first thing that I would do is to get a derailleur adjustment. Front derailleurs can be tricky and every adjustment affects the subsequent ones. Surprisingly, sometimes the high limit screw adjustment can cause the chain throwing that you indicated. Try backing off the high limit screw adjustment 1/8 turn. It it's set too tight it can bind and, when it finally releases, throw the chain across the small chainring. That doesn't cost anything so it's worth a try.

2. There are a couple of $10.00 gizmos that will prevent overshooting your small ring. My high end Santana tandem came from the factory with one.

3. Front derailleurs have to pretty well match what originally came with the bike. Clamp size, cable pull direction, double vs. triple, road vs. mountain, top swing vs. bottom swing. While it's sometimes possible to cheat on some of the above, it's also true that things like water bottle boss locations and flared seat tubes will cause issues more often than you'd think.
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Old 01-19-11, 12:48 AM   #3
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My 6-year-old Cannondale R400 with Tiagra components also had problems holding adjustment on the triple-chainring front derailleur. For some reason the limiter screws on the front derailleur were so loose they couldn't hold their position-- It got so bad that I had to adjust the limiter screws to prevent overshifting before each ride.

The bike mechanic at the LBS looked at my FD, removed the limiter screws, applied some thread-locking compound to them, and put the limiter screws back. Apparently that did the trick-- My Tiagra FD stopped its erratic behavior and can now hold its adjusted positions pretty well.

Your problem sounds a lot like what I experienced.. Maybe check and see if you also have loose FD limiter screws.
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Old 01-19-11, 06:56 AM   #4
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Keep in mind, I have low end components... Sora in the front and Tiagra in the back - which is probably part of the problem.
I doubt it. Most shifting problems are adjustment/cable related -- Given that your FD is actually designed to be used with your chainrings, I'd be $100 you won't notice ANY difference in your shifting by replacing your FD.

Shift to your smallest chainring and largest rear cog and set the low FD limit screw so that the FD is *almost rubbing on the chain. I usually adjust it until is actually is rubbing, then I back it off just a bit. If it's a triple crankset -- you may need to back it off even a *little more to get good shifting to the small ring.

Check your High limit like the above ^^ mentioned.
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Old 01-19-11, 08:20 AM   #5
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Interesting, My Tiagra FD has gotten bad about dropping the chain off of my small ring here lately (compact double) and occasionally off the big one too. I have been making small adjustments to no effect. I will eventually have to take it to the shop and have a pro look at it. I just consider it good practice as I have gotten pretty good at riding it back on.
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Old 01-20-11, 08:44 PM   #6
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Thanks for the advice guys. I'll tinker with it a little more this weekend and see what happens.
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Old 01-20-11, 08:45 PM   #7
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One more thing... If I did decide to upgrade my derailleurs (both front and back) to 105's, would i notice a big difference? Will it be a lot faster? Smoother?
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Old 01-20-11, 09:38 PM   #8
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LongIslandTom's suggestion sounds good to me. Front derailleurs don't really have to do much--I've never had one that didn't work perfectly--and you can probably fix the one you have. Beeswax or threadlock or even a dab of paint on the limit screws should keep them from backing out. Also check the alignment of the cage and the distance between the cage and the chainrings. Parktool.com has a good section on that.
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Old 01-21-11, 04:25 AM   #9
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I agree with all the adjustment suggestions so far, and have one to add. If the chain is too long, a downshift to a smaller ring can throw it off the inside. A couple of links can make a world of difference. Removing 2" of chain from one of my bikes completely eliminated the problem, without touching the FD or its adjustments.

As for Sora vs. "better" groups, I have an 8-speed Sora bike and a 10-speed 105/Ultegra bike, both with triples. The Sora bike shifts better at both ends.

This is probably due to using R-500 shifters instead of the 3300 shifters. These shifters are supposed to be Ultegra-grade, and indeed, they feel like the 6500 shifters on my Ultegra/Dura-Ace double bike. From this, I'm beginning to think it's the shifters, not the derailleurs that make the difference in shifting feel and smoothness.
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Old 01-21-11, 06:58 AM   #10
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Originally Posted by TrekmanDan View Post
One more thing... If I did decide to upgrade my derailleurs (both front and back) to 105's, would i notice a big difference? Will it be a lot faster? Smoother?
How thinly can you slice the baloney?

Shimano has 5 road component groups. The upper end ones are a little nicer in every way but all of the groups do the job adequately and the price shoots up exponentally. My rule of thumb is my threshold for sensing any functional difference is 2 groups. If I move up or down just one group I can't feel any functional difference at all.

Last edited by Retro Grouch; 01-21-11 at 01:48 PM.
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Old 01-21-11, 10:38 AM   #11
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Just my personal opinion/experience here: FDs have always been a little more fickle than RDs. Try the adjsutments ideas listed above before changing anything. I personally like simplicity, so I always try to go with a double front chainring set-up; I've never been able to get a triple to run correctly. I even have a double on my MTB (but I don't do any riding on really aggressive terrain, either!).

As long as you stay away from Wal-Mart-quality level FDs, you shouldn't see a whole lot of difference in front shifting, especially true if you're a recreational rider that's not really 'pushing' the limits of your rig.
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