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PostPosted: Wed Aug 06, 2014 9:45 pm 
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In their last generation (big) chainrings, Shimano has used updated spacing/profile reduces cross-chain contact. As I have not owned a lot of different bikes and groupsets, what is the situation with other manufacturers cranksets?
Being on a small-small gear, does the chain rub against the big chainring with a Campy SR, SRAM Red or Rotor crankset?

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Posted: Wed Aug 06, 2014 9:45 pm 


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 Post subject: Re: Chainring design
PostPosted: Wed Aug 06, 2014 11:23 pm 
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Design aside, chain angle matters. That is metal on metal and reducing the pressure can't do anything but help.
Tony Martin (in TDF TT) used a 58 front to get the chain alignment better.

For my kid in TTs we milled off the 12,13T and his highest gear is in the 3rd position.


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 Post subject: Re: Chainring design
PostPosted: Thu Aug 07, 2014 7:51 am 
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It depends on a lot of thing. Essentially a chainrubs if the angle from small chainring to smallest sprocket is acute enough that it contacts the rings. Obviously the longer the chainstay - the longer that lateral travel is spread over the less acute the angle is - the less chance of chainring rub. A loss of time the rub actually occurs on the inside of the derailleur cage. SRAMs Yaw FD has decreased this so that you can run small/small without rub but it is still a bad gear to be in as your drivetrain resistance will be higher. SRAM did revise their chainring spacing for this. I imagine that chainrub is more of a problem with compact setups with wider jumps from small -> big ring ie 16 tooth rather than 14 tooth standard jumps as the outer ring is now extends further backwards relatively to the small ring thus getting in the road of a crossed chain.

Curious why you are asking this? If you are rubbing your chain so much that it bothers you on a modern setup - you either need to get your FD adjusted or shift up to big ring sooner.

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 Post subject: Re: Chainring design
PostPosted: Thu Aug 07, 2014 10:39 pm 
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Good point about the chainstay lenght, didn't cross my mind.

I have a Scott Foil, Rotor 3d+ cranks and oval chainrings (110bcd, 53/38) with specific bearings to run it in a PF86 frame. I can't use 11, 12 and 13 sprockets when being on the small chainring. 13 is sort of ok, but still slight rub. What I want to archieve is to switch to a Shimano crank (for easier servicing), but keep the oval chainrings. Also, having at least 12 and 13 working without rubbing against the big chainring (not FD).
But it seems Shimano is the only one using offset spacing in their big chainrings and Foil does have short chainstays.

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 Post subject: Re: Chainring design
PostPosted: Fri Aug 08, 2014 10:09 am 
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FWIW I have the new Sram Red crank and no rub at all. I would get it on the smallest cog when in the 39 with my Zipp VumaQuads. The new Red's are 100 grams heavier than the VumaQuads but quite solid.

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 Post subject: Re: Chainring design
PostPosted: Sun Aug 17, 2014 2:06 am 
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Something not being discussed is chain tension. Small/Small puts more tension on the chain than the same gear with big and slightly bigger.
45X12 is about 53X14
Bigger is heavier and the chain needs to be a couple lengths longer - so 10g there - (this is a weightweenies site) - and I guess less aero :-/

On the tandem in the old days when moose 1 and moose 2 rode that tension in the sync chain and drive chain and was noticeable and the frame felt it too.

My son tells me he feels the difference and we will be going bigger ring for TT soon - plus it just looks cool.


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PostPosted: Sat Nov 29, 2014 4:23 pm 
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I use 3D+MAS 110BCD, 52/38 with a DA 12-28 and Shima DA 9000 group. Works flawless, no chainrub!


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PostPosted: Sat Nov 29, 2014 5:40 pm 
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...chain tension has nothing to do with the inner cage rubbing that the OP is describing in the crossed gear configuration. The issue is a function of what Nifty describes (chain stay length and der adjustment) in addition to fact that OP is using OVAL chainrings. Specifically, the OP needs to experiment with correct der height and angle in order to accommodate as many gears as possible with the OVAL chainring configuration, knowing that optimal shifting and the range of gears that are usable will not be the same as when using round chainrings. Lastly, 11 speed chainrings (from most manufacturers) are slightly narrower to accommodate the narrower chain and I don' think that has anything to do with accommodating more cross chain. Rather what has changed is the spacing between the chainrings as has the width of the front der cage/ EM3

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PostPosted: Sat Nov 29, 2014 5:56 pm 
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I also bought oval rings, but only Q-rings.
For usage of QXL chainrings, you'd need these adapters:
http://www.velotechservices.co.uk/shop/ ... 1624&cat=2
This is to angle the FD correct. I have this kit, but it is not needed for Q-rings.
I bought it just to have in case. It is included with Rotors own QXL rings.
I have no clue of how difficult it is to set FD for QXL rings, but for Q rings only thing that is obvious, is the height of the FD compared to round rings.
Setting it up for good shifting, was not really a problem.
I might say i have only tried with Shima DA 9000 using DA 9000 chain and cassette (if it matters).
What i have been noting, is the Sram Red or any FD with YAW, is told to work rather bad. I think this may be due to the YAW constuction.
With Campa and Shima it seems to work well.


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PostPosted: Sat Nov 29, 2014 7:39 pm 
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This is one reason why I have never liked the modern trend of ultra-short chainstays. I like a minimum of 410mm. I don't see a downside to having a few extra mm on the chainstay, and it makes chain line a lot better.

I read an interview with a SRAM rep who said SRAM INCREASED the space between rings on the 22 design to give more clearance when at the extreme positions. I went from a Red 10 speed crank to a Red 22 crank (on a 10 speed setup, chain) and it is indeed quieter and works fine even on 10 speed.
I am not sure if shimano did the same, but an Ultegra 6800 also works flawlessly on 10 speed with 10 speed chains.

(I am too cheap to go full 11 speed. I was just upgrading cranksets)


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PostPosted: Sun Nov 30, 2014 3:13 pm 
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I've been using osymmetrics with a 14t difference on a ultegra 6800 cranks with 405mm chainstays without issue.


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Posted: Sun Nov 30, 2014 3:13 pm 


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