# Cross-chain noise - chain rubbing chainring



## OldZaskar (Jul 1, 2009)

I was helping a buddy dial in his FSA/105 bike yesterday and came across something that was a first for me: When cross-chained - small chain ring + small cog, the chain would rub the large chain ring and make a whole lotta noise, similar to when the chain rubs the front derailleur. 

I told him A) Cross-chaining that way - as opposed to big ring + big cog - isn't very common, so he should just B) Avoid it, because C) There's no way to adjust it away.

Ever seen this? Is there a simple fix?


----------



## matfam (Jul 13, 2012)

Same thing happens on my Allez. I rarely ever cross chain so and have not tried to fix that issue.


----------



## Mr Evil (Aug 12, 2011)

Seems to be quite common on modern drivetrains. I fixed it on my bike by swapping spacers on the BB to move the chainrings 1mm further out, but that wasn't really necessary as I never use small-small.


----------



## Agent319 (Jul 12, 2012)

What's the tooth count on the small and large chainrings?


----------



## Camilo (Jun 23, 2007)

This has been a factor ever since I started riding multispeed bikes in the 70s. Cross chaining small-small often (usually?) causes chain rub on the big ring. Maybe just odd experience on my part, but I've never considered small small to be something that was a viable or smart option.


----------



## OldZaskar (Jul 1, 2009)

Camilo said:


> This has been a factor ever since I started riding multispeed bikes in the 70s. Cross chaining small-small often (usually?) causes chain rub on the big ring. Maybe just odd experience on my part, but I've never considered small small to be something that was a viable or smart option.


I checked my bike (7900) and it doesn't do this. But - to your point - I wonder if I've wrongly attributed chain-to-chainring rub to the front derailleur, on other bikes. And yeah, small-small is easy to avoid.


----------



## tihsepa (Nov 27, 2008)

OldZaskar said:


> I checked my bike (7900) and it doesn't do this. But - to your point - I wonder if I've wrongly attributed chain-to-chainring rub to the front derailleur, on other bikes. And yeah, small-small is easy to avoid.


Its really only an issue on bikes with compact chainrings. There may be some compacts that dont have this issue but I am guessing not many. 
Also, the length of the chainstay will effect wheather or not there is rubbing.


----------



## Drew Eckhardt (Nov 11, 2009)

OldZaskar said:


> I was helping a buddy dial in his FSA/105 bike yesterday and came across something that was a first for me: When cross-chained - small chain ring + small cog, the chain would rub the large chain ring and make a whole lotta noise, similar to when the chain rubs the front derailleur.
> 
> I told him A) Cross-chaining that way - as opposed to big ring + big cog - isn't very common, so he should just B) Avoid it, because C) There's no way to adjust it away.
> 
> Ever seen this? Is there a simple fix?


My "9 and 10 speed compatible" FSA Carbon Pro Compact 50/34 rings were spaced tighter than Campagolo 10 speed and produced chain rub on the last few cogs producing _zero_ usable overlap between small and big ring.

Thin shims (LeTour makes 0.6mm shims specifically for 9 to 10 speed conversion) allowed all cogs to run without rub.

(Presumably this was exacerbated by my 40.6cm chain stays and Campagnolo C9 chain which was obviously wider than 10 speed width and was the last to not have recessed rivets)


----------



## Mr645 (Jun 14, 2013)

I get a slight rubbing in the other end, big front, big rear. Often when climbing, the big/big using a compact crank and 11-28 cassette is enough to get up many hills and bridges so it saves me the trouble of shifting the front. There is a slight rubbing but a few bike techs have said it's fine, won't cause any damage


----------



## OldZaskar (Jul 1, 2009)

Mr645 said:


> I get a slight rubbing in the other end, big front, big rear. Often when climbing, the big/big using a compact crank and 11-28 cassette is enough to get up many hills and bridges so it saves me the trouble of shifting the front. There is a slight rubbing but a few bike techs have said it's fine, won't cause any damage


^That^ is the chain rubbing the front derailleur. Most techs say it's fine... 'cause they don't want to be bothered with adjusting the front derailleur. And yeah, it won't hurt anything... it's just annoying - especially when you know it's avoidable.


----------



## OldZaskar (Jul 1, 2009)

tihsepa said:


> Its really only an issue on bikes with compact chainrings. There may be some compacts that dont have this issue but I am guessing not many.
> Also, the length of the chainstay will effect wheather or not there is rubbing.


I hadn't thought about the chainstay length - it makes perfect sense. And of course the difference in size between the two rings.


----------



## cxwrench (Nov 9, 2004)

Mr645 said:


> I get a slight rubbing in the other end, big front, big rear. Often when climbing, the big/big using a compact crank and 11-28 cassette is enough to get up many hills and bridges so it saves me the trouble of shifting the front. There is a slight rubbing but a few bike techs have said it's fine, won't cause any damage


Either you're not using the trim function OR you know some sh*tty mechanics.


----------



## Kerry Irons (Feb 25, 2002)

OldZaskar said:


> ^That^ is the chain rubbing the front derailleur. Most techs say it's fine... 'cause they don't want to be bothered with adjusting the front derailleur. And yeah, it won't hurt anything... it's just annoying - especially when you know it's avoidable.


It can be more than annoying. I've seen people wear right through the FD cage by riding continuously with the FD cage rubbing on the chain. The hardened steel of a chain is much harder than the derailleur cage.


----------



## Kerry Irons (Feb 25, 2002)

tihsepa said:


> Its really only an issue on bikes with compact chainrings.


It's quite common on bikes with 53/39 rings as well. It's all about chainstay length and the chain line.


----------



## Roland44 (Mar 21, 2013)

matfam said:


> Same thing happens on my Allez. I rarely ever cross chain so and have not tried to fix that issue.


Yeah same here, I keep saying it's nothing important but I really have to fix it someday soon.


----------



## Mr645 (Jun 14, 2013)

cxwrench said:


> Either you're not using the trim function OR you know some sh*tty mechanics.


It can be almost tuned out, but the clearance on either end, small/small or big/big is very slim so even trimming the FD it's very hard to keep it perfectly clean. As long as the shifting is smooth and precise I have not been worrying much about it. I don;t spend much time crossed


----------



## bigjohnla (Mar 29, 2010)

I have a Bianchi infinito with 105 and a compact FSA crank set. I have never had problems with this as long as I kept the front derailleur properly adjusted. However, the difference between properly aligned and out of whack is very minute. It is something I check often.


----------



## cxwrench (Nov 9, 2004)

I'll always bias the way I set a front derailleur up so that it will work big/big if it's at all close or hard to set up so both big/big & small/small will work. Small/small is only good for one thing...sizing chains. Big/big comes in handy in numerous situations.


----------

