Bicycle Mechanics - Why won't my Ultegra trim

Just wondering why my front derailleur won't trim. My understanding is that when you are on the big ring in the front and the large cog in the back you should be able to lightly hit the small lever (the one that shifts to the small ring) and it should move the front derailleur slightly to eliminate any rubbing. Mine won't do this. Is this improper adjustment or is there something wrong with my front derailluer or shifter. This bike is only about 1.5 months old.

dbl or triple

dbl or triple

DOUBLE.... but it was converted at the lbs from a triple. As far as I can tell it has the correct f.dr. on it.

On my Ultegra, it's very difficult to trim from big ring to small ring. Trimming from small ring to big ring is easy though. I must say on the Campy Mirage bike I'm building up the trimming on the FD is a dream to use, both ways.

I found that it took about a good 800 miles on my shifter to really get the trimming down. Whether this is the shifter or me just getting used to it I'm not sure, but it works fine for me right now.

My understanding is that when you are on the big ring in the front and the large cog in the back

My understanding that the big/big combination is one to be avoided...too much stress on the drivetrain. Why not switch to the small chainring in such circumstances?

My understanding that the big/big combination is one to be avoided...too much stress on the drivetrain. Why not switch to the small chainring in such circumstances?

yes it is...

But there are times that you only need to use it in such short time, say under 2 mins when battling a short incline, then afterwards you shift to a harder gear when at the top. That's why trimming is there....

You will never trim away all the chain rub in the big/big combo no matter what gruppo you are riding. With todays 9 speed setups, especially if you have shorter chainstays, the angle is just too great. That is why the actively discourage the use of that type of gear selection. If it is just a short incline stand up and grunt it out in a harder gear.

I empathize with you. I have problems with big to big, and small to the 3 smallest cogs in the rear (I have a triple). The bike shop just tells me that's the way it is. It's kind of frustrating to pay so much for a bike and it doesn't work quite right.

Boomer-

It works fine within the parameters of practical mechanical design. You will never be able to use all 27 theoretical gear combinations. The laws of physics won't allow 2 objects to occupy the same space, so the chain can't be where the FD cage is.

Just wondering why my front derailleur won't trim. My understanding is that when you are on the big ring in the front and the large cog in the back you should be able to lightly hit the small lever (the one that shifts to the small ring) and it should move the front derailleur slightly to eliminate any rubbing. Mine won't do this. Is this improper adjustment or is there something wrong with my front derailluer or shifter. This bike is only about 1.5 months old.

Yeah, this can be a little difficult to do sometimes, especially if the tension on you cable is a little tight. It a finess move and you need to develop a feel for it Both my wife's and my bike have Ultegra's, but it's a lot easier to trim on her bike than it is on mine. It took a little practice for me to get the feel for it on my bike, but once I did, I can finess it. Of course, I did this before I knew about cross-gearing. Now I don't run big-big or small-small anymore, so I don't really need to trim anymore.

My understanding that the big/big combination is one to be avoided...too much stress on the drivetrain. Why not switch to the small chainring in such circumstances?

I should have been more specific in my first post. I'm actually having rubbing start when I'm in the big ring and maybe the third cog from the biggest in the back. This is where I understand that the trimming should help by moving the F.DR. towards the small ring slightly. I do realize that large ring to large cog is not the best way to ride. On my bike, when I hit the downshift lever (the small one) there is no intermediate click and therefore it will not move the F.DR. slightly towards the small ring. It will only make the large movement towards the small ring.

Well, I find the big-to-small trim almost impossible to use on my Ultegra (dbl) and my wifes 105 (triple). It's d*mn near impossible to press the levers with the right force while riding. Either not hard enough (no shift), or too hard (complete shift). I doubt that's your problem, but I'm just sayin' you aren't missing much, IMO.

On the other hand, if you're riding a double, you should be able to adjust the cage such that you don't get rub until you're actually on the large rear cog.

Maybe it is time for the post break-in tune up, which is generally a free service from the LBS you bought the bike from. New cables stretch for a while, and this can affect shifting quality as well as ability. This gives the shop a chance to make sure that everything is working, is adjusted correctly and that all fasteners are properly tightened.

Are you sure that when you shift onto the large chainring that you are fully engaging past the intermediate indent?

If not then when you go to try and trim you will shift down to the small chainring. Next time that you upshift or if you are already on the large chainring nudge the lever a little further that is necessary to make the required shift.

trimming "down" is much harder than trimming "up"

the mechanic at my LBS said that when trimming down, instead of pushing the shifter directly across as you woulld to shift, to *push forward* on it a little too.

this seems to work pretty well, though i've also found that the shifters need a break in period of 400 miles or so--then trimming becomes much easier.