Adjusting front derrailler...
 

question: Do the limit screws affect the middle position (3 chainrings) of a front derailer at all? I recently adjusted one of my limit screws to allow more movement inward toward the small ring, but it seems now it is rubbing when on the middle ring.

Answer: No.

the issue of rubbing , I'm guessing is the STI shifter, since friction shifters can be trimmed by You with the shift lever.

direct answer... yes but no.

moving the limit screw will slightly alter cable tension and thus affect middle position on a triple.

i learned that when adjusting lower limit screws, its best done with no tension on the cable (or cable not hooked at all)

The front derailleur's position when it is in the middle-ring position is determined by the shifter, not the derailleur. But the low limit screw does play a role in determining where the shifter places the front derailleur when moved to the middle ring position.

If the low limit screw is set so that the inside cage of the front derailleur is not close to the inside (low) ring, it won't shift properly to the middle ring. As that limit screw is tightened and the cage moves closer, the front shifting will improve such that it makes the jump to the middle gear. However, if the cable is tight after making the low limit screw adjustment you may need to take some of the tension out so that the front derailleur can swing as far out as it needs to and this is where middle ring performance is most greatly affected.

Return the chain to the low (smallest) front chainring and low (largest) rear sprocket and check the cable tension. If you've already made the low limit adjustment, let out any cable tension by loosening the cable clamp bolt and let the tensioned cable slide back through. Now tighten it up and take out any remaining slack with the cable adjusters. (You may want to dial in your cable adjusters before you start.)

Now your shifter will begin it's swing where you set the low limit screw. With the bike in low front and low back, the inner front derailleur cage will need to be near the low chainring. (It can get pretty close when in this gear combination because shifts to a higher gear will only move the chain further away from the front changer cage.)

If you still have problems with the shift from middle to low chainrings, check first that when the changer is in low that there's little or no tension on the cable. If that checks out, back out the low limit screw 1/8 of a turn and check to see if the middle to low shifting has improved. Repeat as necessary keeping an eye on cable tension and using the cable adjustment barrel to compensate for too much or too little tension.

NO. this is wrong.

The limit screws are exactly what their name implies. They set the extreme inside and outside limits to the derailleur range. Think of them as the concrete barriers along the sides of a bridge so you can't drive too far to the side and into the drink. Te barriers determine the road width, but you have to choose and drive in the lanes.

The derailleur's mechanism hangs from the cable, and that determines it's position.

However, in practice there's an exception. Most derailleurs (both front and rear) are designed so the cable is overly slack in the slackest position (high in rear, low in front) and the derailleur is allowed to rest on the corresponding limit. So, the inside FD limit does affect the trim in low, but that's the only gear where it's used for trim.

I'm just saying.. Indexing is fussier than a simple friction Lever.. OP doesn't say what the shifter is , so I throw out a Guess..

FYI, it is shimano trigger shifters on a hybrid. I haven't had a bike with friction shifter since....well, 2014.

that ads complexity in trying to make shifting simpler..

This is assuming that the derailleur limits are adjusted with the cable being slack or not attached and that it's allowed to rest on the stops (the correct way to setup a derailleur)

If the cable is attached to the derailleur and then the limit screws are adjusted, the derailleur won't be resting on the stops.

case in point, OP adjusted low limit and now cable tension has clearly changed. thus, it wasn't resting on the limit stop.


OP should have an inline barrel adjuster on the cable somewhere (at the shifter) that should help him trim the noise out.

the better question should be: why did the OP feel the limit needed to be adjusted to allow more movement inward.

Do you really think that adjusting after each and every shift, instead of setting-up properly just once, is simpler?

I want a lower gear, I pull a trigger or tap the shifter, and I'm there. One step, finished.

When I was on my friction shifter, I moved the lever to shift, I adjusted the shift. Two steps, finished.

If I didn't have to adjust the shift after moving to a higher or lower gear in the back, I almost certainly had to adjust the front changer to allow for chain bend as the rear sprockets are traversed.

The OP backed out the low limit screw because he was having difficulty shifting from the middle to low.

I think I see what you're getting at, but the limit screws should always be set first with no cable attached and then the cable tension should be set AFTER for correct shifting.

On a properly setup system, if the limit screws are messed with but the cable tension is not changed, shifting to the middle ring position will NOT be altered.

YMMV, obviously

I have been riding thru a Dozen Countries without problems on bike tours for 30 years and have been fine with a set of bar ed shifters ..

for all that Time ( recently opted to IGH for most of My Use Now**

maybe you want instant Electric switch like shifting Manufacturers are catering to your buying , Di2 the next Item in walletectomys.

I fix the stuff on the repair stand , Just dont Own any .. (now the youngsters take over the bike shop jobs..)

Un said is riding technique ,, do you let up on the pedal Force so the mechanism can work?

1. I had the bike tuned up by the LBS around last June...it shifted well then...recently, it would not andshift to the small chainring unless the rear derrailler was on the largest gear. I loosened the lower limit screw to allow more movement...it worked somewhat, but it still isn't ideal...

2. The problem persist even surfing easy spinning...it is not a shifting under load issue.