FD Capacity, Any Margin?

[sathomasga]

I'm considering swapping out my standard Ultegra double crankset with an FSA Compact, which is a 50/34 crankset. According to the Shimano web site, the Ultegra double FD has a capacity of 15T, which, alas, is one less than the FSA crankset requires.

Question Set 1: Does anyone have any experience or intuition on the effects of running a 50/34 with this FD? Is it going to work at all? What, if any, will be the compromises?

Question Set 2: The Ultegra *triple* FD has a spec'd capacity of "22(triple)." The "triple" in parenthesis has me worried. What, if anything, can be said about capacity when using the triple FD with a double cranket? Is it going to be any better than the double FD?

Question Set 3: If I do have to go with the triple FD, will I lose the trim positions that are present with the double? I find myself using them extensively now. I have read reviews, however, that said the FSA cranks had much less chain rub because of their stiffness. Will this eliminate the need for trim positions?

Many thanks in advance.

 

[miamijim]

Trim settings are in your levers not the derailleur.

You can probably use the double beyond the 15T capacity. what usually happens is if your in the small cog in the rear the chain drags on the lowest part of the derailleur cage. If you only shift into second smallest cog your difference is now 14T.

Triples can be used on doubles with no problems......doubles cannot be used on triples.

Chain rub is fact caused by flex.....if you adjust your trim to compensate for rub when your pushing down then a stiffer crankset may help...remember you might be getting most of your flex from the frame which will rub....spin spin spin

 

[boudreaux]

Originally posted by sathomasga
I'm considering swapping out my standard Ultegra double crankset with an FSA Compact, which is a 50/34 crankset. According to the Shimano web site, the Ultegra double FD has a capacity of 15T, which, alas, is one less than the FSA crankset requires.

Question Set 1: Does anyone have any experience or intuition on the effects of running a 50/34 with this FD? Is it going to work at all? What, if any, will be the compromises?

Question Set 2: The Ultegra *triple* FD has a spec'd capacity of "22(triple)." The "triple" in parenthesis has me worried. What, if anything, can be said about capacity when using the triple FD with a double cranket? Is it going to be any better than the double FD?

Question Set 3: If I do have to go with the triple FD, will I lose the trim positions that are present with the double? I find myself using them extensively now. I have read reviews, however, that said the FSA cranks had much less chain rub because of their stiffness. Will this eliminate the need for trim positions?

Many thanks in advance.

It works with a double derailer. Crank stiffness and chain rub is bull.

 

[boudreaux]

Originally posted by miamijim
Trim settings are in your levers not the derailleur.

You can probably use the double beyond the 15T capacity. what usually happens is if your in the small cog in the rear the chain drags on the lowest part of the derailleur cage. If you only shift into second smallest cog your difference is now 14T.

Triples can be used on doubles with no problems......doubles cannot be used on triples.

Chain rub is fact caused by flex.....if you adjust your trim to compensate for rub when your pushing down then a stiffer crankset may help...remember you might be getting most of your flex from the frame which will rub....spin spin spin

You are confusing front and rear capacity when you talk about shiftng to the 'second smallest cog'. Double FD often work with triples. Chain rub on the derailer is very often NOT caused by flex of either the crank or frame. You can get derailer rub on a repair stand.

 

[miamijim]

boudreaux...everything I posted is correct.....I am not confusing front and rear capacities......

If chain rubs not caused by flex them what causes it? Besides bent crankarms and rings?????

Remember the second cog is a lrger diameter which will raise the chain away from the derailleur giving a clearance similar to having a 14T difference.....

 

[boudreaux]

Originally posted by miamijim
boudreaux...everything I posted is correct.....I am not confusing front and rear capacities......

If chain rubs not caused by flex them what causes it? Besides bent crankarms and rings?????

Remember the second cog is a lrger diameter which will raise the chain away from the derailleur giving a clearance similar to having a 14T difference.....

Sorry,but you are confused. Certainly, using a bigger rear cog will do away with the rub if the chain IS actually dragging on the tail of the derailer. But you should not be in the small small anyway.Never had that happen if the FD curvature was matched to the chainrings. Rub on the sides of the derailer cages is much more common and can happen with frames that absolutely do not flex and with stiff cranks and perfect chainrigs. Causes:misaligned derailer,misadjusted hi or low limit screws and or not trimming the FD...Remember too, speced capacities are usually conservative and often reflect the combinations that the manufaacturer is selling,not what the equipment will actually do when used in other combinations.