Chainring & f mech compatibility

For discussions about bikes and equipment.
peetee
Posts: 1416
Joined: 4 May 2010, 10:20pm

Chainring & f mech compatibility

Postby peetee » 30 Jan 2018, 10:48am

I was thinking about buying a 105 or ultegra 2x11 groupset but don't like the standard wide spacing of the chainrings. I have seen issues in the past (specifically on triple groups) where the ramps on the front mech mean changing the inner chainring size can be a hit and miss business.
If i were to change the set up from a 50-34 to a 50-39, say, would that create a gear shift issue?
Current status report:
Latter side of fifty and feeling less than nifty.
Too many bikes on pegs and too few miles in the legs.

User avatar
willcee
Posts: 917
Joined: 14 Aug 2008, 11:30pm
Location: castleroe,co.derryUlster

Re: Chainring & f mech compatibility

Postby willcee » 30 Jan 2018, 12:17pm

Afaik this groupset is 4 arm so 110 BCD and is offered with choice of pro gearing 39/53, semi compact 36/52, or compact 34/50... i have 2 of differing ratios on 2 of my machines and have used the 11sp pro gearing on a bike i built and ''run in'' for a chum.. care when setting up the front meck is always needed on any 11sp as the front derailleur and sti lever use very high cable tension to overcome imo a poor cable angle and the long lever at the meck, there is a supplied guage to assist in getting the correct ''in Shimanos view'' cable run to the pinch bolt..so i don't really see any difficulty everything else being normal.. famous last words!! will

peetee
Posts: 1416
Joined: 4 May 2010, 10:20pm

Re: Chainring & f mech compatibility

Postby peetee » 31 Jan 2018, 11:19am

S'ok. I have built up a few 11 speed systems. Setting up the front mech is a case of ignoring everything your experience tells you and reading the instructions instead (urg!).
If the pcd on the 105 cranks doesn't vary (ie 110 OR 130) then a 39 tooth could be substituted for a 34 but when I tried change the middle ring on a deore crankset I had to adjust the front mech so the inner cage plate didn't foul the middle ring when using the outer ring. That put the shift ramps in the wrong place and upshifts were terrible. I was just hoping someone might have done a ring swap on a racing group and could tell me if it works. Surely I can't be the only one who hates the wide gap on cranksets these days. Bring back 42-52!
Current status report:
Latter side of fifty and feeling less than nifty.
Too many bikes on pegs and too few miles in the legs.

PeterBL
Posts: 166
Joined: 26 Oct 2010, 1:04pm

Re: Chainring & f mech compatibility

Postby PeterBL » 31 Jan 2018, 12:21pm

You don't have the issue with the cage fouling the middle ring when you are on the outer ring with a double front mech. So it should work, but I can't tell you I have done it.

Brucey
Posts: 35930
Joined: 4 Jan 2012, 6:25pm

Re: Chainring & f mech compatibility

Postby Brucey » 31 Jan 2018, 12:57pm

peetee wrote:I was thinking about buying a 105 or ultegra 2x11 groupset but don't like the standard wide spacing of the chainrings. I have seen issues in the past (specifically on triple groups) where the ramps on the front mech mean changing the inner chainring size can be a hit and miss business.
If i were to change the set up from a 50-34 to a 50-39, say, would that create a gear shift issue?


in general double FDs on double chainsets are a bit more forgiving than triple FDs on triple chainsets.

The specs for FD-5800 read '16T maximum interval' but it doesn't give a minimum value. You can estimate this by measuring the depth stagger in the FD. Allow about 2mm per tooth, so if you want an 11T capacity then anything over 22mm ought to ring warning bells. I don't think it will be a problem, current shimano 2x11 FDs look shallower than that.

BTW one of the standard FC-5800 setups is indeed 53-39T . The chainrings are all 110mm BCD uneven four-bolt (just what the world needed, another standard.... :roll: ) I don't know what happens if you pair a 50T or 52T with the 39T inner; it is possible that the shoulders on the big ring won't be right and this may cause a problem; a lot of big rings have a very slopey left side and this cannot work with every chainring combination. I am worried specifically that the chain may be able to sit on top and to the right of the 39T chainring teeth.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~