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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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Joined: Wed Oct 30, 2013 12:52 am
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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
Posted: Fri Aug 08, 2014 10:09 am 


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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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