Front derailleur/chainring gap

[py3gemini]

I am trying to upgrade my 50/34T 105 chainset to an Ultegra 6800 46/36T system with all the appropriate 6800 components
Unfortunately there is not enough adjustment on the braze on front derailleur to enable me to achieve the recommended 1 - 3mm gap between the top of the big ring teeth and the bottom of the derailleur. The closest I can get is 4.5mm due to the smaller diameter of the 46t chainring.
I am not sure how critical this is but if it is critical to the smooth working of the system then the only solution I can see is to buy a new 50/34T Ultegra chainset which I don't really want to do.
Any ideas anyone ?

[cradom]

Is there enough metal around the hole to file slots in it so you can get closer?

[cny-man]

Will a 48-34 do the trick - offers a more useful high end with a 11 or 12 tooth small cog.

[GingerTart]

I had the same problem.

I removed an Ultegra 52/39 chainset and replaced it with a 50/34 compact chainset. The gap between the front derailleur and the new 50T chainring is around 5mm, and I can't lower the derailleur any further.

Front shifting with this new set-up isn't great, but its good enough to do the job. Occasionally, after clicking the shifter lever, I may need 2 or 3 turns of the pedals to shift the front chainring, it depends on the power that I'm exerting at the time. Not ideal to pull back at a critical moment, but its worth the sacrifice in order to have the compact chainrings and so save my knees from long-term damage.

[nfmisso]

(01-22-2015, 06:51 PM)GingerTart Wrote:  ....., but its worth the sacrifice in order to have the compact chainrings and so save my knees from long-term damage.

Interesting; my knees have the opposite issue: they do not like the 32% difference between the 50 and 34 tooth rings, the 25% difference between 52 and 39 is much better. The 46/34 combination provides a 26% difference, probably chosen to be as close to the same percentage as 52/39.

I am planning on changing from 50/34 to 52/39 on my WT, and compensating with larger cogs on the cassette (currently 7 speed 13-26; going to 8 speed custom 14-32 [13-26 minus the 13T and 14T cogs, with a 32T add and 14T first position cog]). The 52-14 combo is about the same as 50-13 and the 39-32 is a bit lower than 34-26.