Derailleur adjustment with compact crank

[HillSlugger]

You should have some. Often the derailleur and the braze on fall in love in a certain position, but if you hold the derailleur firmly in the alternative, more ideal position, it should move a bit for you. Definitely try it again...what have you got to lose? Derailleur adjustment stuff tends to be finicky more often than not, and so often requires patience and at least a few tries til you find the sweet spot. Good luck.

I had the bike in my car so I could take it by the LBS; the alignment looks good to me.

Anyway, I swung over to the LBS after work. The wonderful mechanics there took a look at it right away, made some adjustments on the spot, and returned the bike to me. Hopefully this will work.

When I wheeled the bike into the store one of the staff said "Wow, what is that? I've never seen a bike like that!" This really made me smile

[divingbiker]

I had the bike in my car so I could take it by the LBS; the alignment looks good to me.

Anyway, I swung over to the LBS after work. The wonderful mechanics there took a look at it right away, made some adjustments on the spot, and returned the bike to me. Hopefully this will work.

When I wheeled the bike into the store one of the staff said "Wow, what is that? I've never seen a bike like that!" This really made me smile

Is this your tri bike you're fiddling with? Did you take it to Proteus or somewhere else?

[HillSlugger]

Yes, the tri bike. I took it to City Bikes since they are the most convenient for me.

[aicabsolut]

If you still have problems, bring it to me. I've used 105, Ultegra, and DA front derailleurs on FSA and DA cranks. The 105 or ultegra setup on the FSA cranks with a clamp-on FD was the most finicky. The DA/DA braze-on match is amazingly awesome. But, if it's an alignment issue, I will be able to fix it. I usually have to totally re-do the FD on the FSA bike after the shop messes with it. So, I learned how to do it pretty well. If the cage needs to be moved, it can be a pain. You don't have as much range with a braze-on, but it can be moved a little bit.

However, I'm thinking that since this is your tri bike with non-indexed shifting in the front, some of it is going to be user error. Maybe you aren't used to the throw of the lever yet. Some compacts are a little more finicky about what rear cog you're in when you shift (are you any more successful shifting from the smaller end of the cassette?). Even so, it should be relatively rare to get the chain to go off to the outside if the FD is adjusted right. It's a lot more common to have drop to the inside with a compact.

You might try re-setting the limit and then tightening the cable tension if it gets a little sluggish. Adjust the FD upper limit screw a TINY bit at a time, and while you're in the little ring.

[ridebikeme]

Lots of great advice here! Working with a compact crank does take a bit more time, but I'm sure that your LBS will get it right. Have fun with the new crank!!!

[HillSlugger]

Instead of doing my Wednesday bike commute I took the tri bike out for a test ride this morning. The good news: no dropped chains! The bad news: I sometimes had trouble getting the chain to go onto the large ring and if I was on the large ring and using the two smallest cogs I had FD chain rub and couldn't trim out to stop it. Obviously I need to move the limit out a tiny bit. Do you think I should do this right away or wait until after my next ride on Saturday? And the stupid question so I can get it right the first time: to move the cage out do I loosen or tighten the limit screw?

[Becky]

Instead of doing my Wednesday bike commute I took the tri bike out for a test ride this morning. The good news: no dropped chains! The bad news: I sometimes had trouble getting the chain to go onto the large ring and if I was on the large ring and using the two smallest cogs I had FD chain rub and couldn't trim out to stop it. Obviously I need to move the limit out a tiny bit. Do you think I should do this right away or wait until after my next ride on Saturday? And the stupid question so I can get it right the first time: to move the cage out do I loosen or tighten the limit screw?

Don't touch the limt screw (except maybe a tiny bit looser to improve shifting to the big ring)! One of the limitations of a compact is that, when you're cross-chained small to small, the chain will drag across the teeth of the large ring. Just don't cross-chain and you'll be fine

I can get to about the third cog from the bottom (14T) with the help of the trim before my chain drags on the large ring. I try to shift to the large ring sooner (15T or 17T), depending on cadence and terrain, but the best laid plans....

[HillSlugger]

Don't touch the limt screw (except maybe a tiny bit looser to improve shifting to the big ring)! One of the limitations of a compact is that, when you're cross-chained small to small, the chain will drag across the teeth of the large ring. Just don't cross-chain and you'll be fine

I can get to about the third cog from the bottom (14T) with the help of the trim before my chain drags on the large ring. I try to shift to the large ring sooner (15T or 17T), depending on cadence and terrain, but the best laid plans....

No, I was big/small, not crosschained.

BTW, when I was at the LBS the wrench told me that my chain was a bit too short because he couldn't get it to go big/big. I pointed out that I shouldn't ever be big/big!

[Becky]

No, I was big/small, not crosschained.

BTW, when I was at the LBS the wrench told me that my chain was a bit too short because he couldn't get it to go big/big. I pointed out that I shouldn't ever be big/big!

Gosh, I'm sorry! I'm not reading very closely again- my fault!

In that case, I'd loosen the high limit screw the tiniest amount (quarter turn or so), and try again. You're almost there, and soon it will be perfect!

[lunacycles]

BTW, when I was at the LBS the wrench told me that my chain was a bit too short because he couldn't get it to go big/big. I pointed out that I shouldn't ever be big/big!

Yes, but you want your bike to be able to do this, should you be in one of your less clear/ more tired moments and accidentally make that shift. If the chain is too short and you accidentally shift "big-big" while riding, it can literally rip the derailleur off the frame, potentially destroying your frame, at a minimum destroying the derailleur. A longer chain also just shifts better.

[aicabsolut]

You shouldn't be using trim at all to avoid rubbing in large ring/small cog combos. The cable should be pulled all the way tight (shifting completely). Trim when in the large ring will help you avoid rubbing the inner part of the cage in the larger cogs.

I would NOT mess with the limit at this point. You are getting rub in the smallest 2 cogs. This indicates that you've probably still got an alignment issue. Can you see where relative to the tail of the cage the rubbing is occurring? When you are standing near the rear of the saddle on the right side, facing forward, and when the bike is in the big ring/small cog, you should be able to look down and see that the chain is centered over the tail of the cage. If it's too far in or too far out, then you will have excessive chain rub despite properly set limits.

Also before you mess with the limit screws, check your cable tension. You are having symptoms of slow shifting and too much chain rub. That could be a limit issue, but I'd be hesitant to go there first given the bike's propensity to throw the chain off the outside. Try testing cable tension first. Hand shift by pulling the cable. Does the rubbing stop when you are pulling on it? If so, then maybe you just don't have the cable tight enough such that when you've got the lever pulled all the way, you aren't getting full movement of the cage (but you can get the additional necessary tension by pulling with your hand).

[aicabsolut]

Yes, but you want your bike to be able to do this, should you be in one of your less clear/ more tired moments and accidentally make that shift. If the chain is too short and you accidentally shift "big-big" while riding, it can literally rip the derailleur off the frame, potentially destroying your frame, at a minimum destroying the derailleur. A longer chain also just shifts better.

This is true, but it is easy to have too long of a chain on a compact if the chainstays are relatively short. That's because when in the small/large combo, you don't have enough chain tension to pull the RD away from the sprockets. With some setups, tightening the Bscrew to its max won't fix that. So, to avoid that, the chain will be a tad short and noisy. But, it shouldn't be shortened so much that the RD is being pulled sharply forward when in the big/big. You still need enough chain wrap to reach this gear and sustain a bit of an S shape in the RD, even if it's noisy.

[lunacycles]

This is true, but it is easy to have too long of a chain on a compact if the chainstays are relatively short.

If your rear derailleur hanger is designed and aligned correctly for the gears and components you are using (e.g., "road") you shouldn't have the rear derailleur guide pulley bumping up against any cog with the b-tension screw adjusted correctly...just hasn't been my experience. Even if this were to be the case, I'd rather live with a little chain noise in the small/large combo than risk ripping my rear derailleur/derailleur hanger off due to a too short chain...

I determine chain length by "dummying it up" in the small/small combo, and ensuring the chain is just short enough that there is no chain rub against the bottom part of the rear derailleur cage in this combo. I then shift through all gears to ensure it can handle them, keeping in mind stated derailleur capacities as stated by the manufacturer. This has never failed me.

And I am trying to understand: what does chainstay length have to do with it? Thanks.

[HillSlugger]

You shouldn't be using trim at all to avoid rubbing in large ring/small cog combos. The cable should be pulled all the way tight (shifting completely). Trim when in the large ring will help you avoid rubbing the inner part of the cage in the larger cogs.

I would NOT mess with the limit at this point. You are getting rub in the smallest 2 cogs. This indicates that you've probably still got an alignment issue. Can you see where relative to the tail of the cage the rubbing is occurring? When you are standing near the rear of the saddle on the right side, facing forward, and when the bike is in the big ring/small cog, you should be able to look down and see that the chain is centered over the tail of the cage. If it's too far in or too far out, then you will have excessive chain rub despite properly set limits.

I think the alignment is OK, but I'm not completely sure.

Also before you mess with the limit screws, check your cable tension. You are having symptoms of slow shifting and too much chain rub. That could be a limit issue, but I'd be hesitant to go there first given the bike's propensity to throw the chain off the outside. Try testing cable tension first. Hand shift by pulling the cable. Does the rubbing stop when you are pulling on it? If so, then maybe you just don't have the cable tight enough such that when you've got the lever pulled all the way, you aren't getting full movement of the cage (but you can get the additional necessary tension by pulling with your hand).

Just checked, I can't make it go any further by hand.

[aicabsolut]

If your rear derailleur hanger is designed and aligned correctly for the gears and components you are using (e.g., "road") you shouldn't have the rear derailleur guide pulley bumping up against any cog with the b-tension screw adjusted correctly...just hasn't been my experience. Even if this were to be the case, I'd rather live with a little chain noise in the small/large combo than risk ripping my rear derailleur/derailleur hanger off due to a too short chain...

I determine chain length by "dummying it up" in the small/small combo, and ensuring the chain is just short enough that there is no chain rub against the bottom part of the rear derailleur cage in this combo. I then shift through all gears to ensure it can handle them, keeping in mind stated derailleur capacities as stated by the manufacturer. This has never failed me.

And I am trying to understand: what does chainstay length have to do with it? Thanks.

Chain wrap length has to do with the size of the large ring, the size of the large cog, and the length of the chainstay. It needs to be long enough to reach from the large ring to the large cog (along the length of the chainstay) without pulling the rear derailleur too far forward.

I can tell you that with a 34T inner ring, a 25T large cog and a smaller, compact race geometry rear triangle, that being one link too long will cause the rear derailleur pulleys to rub the rear cog when in that combo even with the B-screw tightened all the way (how my newest bike was built). There's nothing wrong with the derailleur hangar. I don't have this problem on a bike with longer chainstays or a bike with a 36T inner ring. With a compact, you still need a lot of chain wrap to get into the larger cogs while in the big ring, but then there's even more chain slack when in a 34T ring compared to standard cranksets. Of course being one link too long also causes a little bit of rub on the bottom part of the pulleys sometimes, but this isn't a problem functionally. Not like having the derailleur body bumping against the cog. I used a chain length calculator and verified that the chain was one link too long. Removing it still requires the B screw to be all the way tight, but there's no more bumping. There is more noise in the big/big combo, and I'm sure there's rougher tension on the chain when in the big ring by looking at the RD pulley angles, but it was necessary.


MDHillSlug, I guess you can try loosening the H limit now some, but do it slowly. Like 1/8 of a turn at a time, then re-check the shifting. You might want to put up with a little bit of rubbing if you don't use the small cog a lot, if that helps you keep the chain on.