Chain rub on certain gears!!

[neil16377]

Hi.
Wondering if anyone can help me out, I have a bike with ultegra 6800 52-36. 11-28 cassette.
The crank is a FSA si

Everything is new on the groupset- the hanger is straight .
But I get chain rub on the highest gears and the lowest crank cog 36t. Chain hitting the crank !!
There is no apparent Rub on the front derailleur at all,

What am I missing?? Cheers

 

[Mobytek]

Crank arms bent!!?!

What you say seems imppssible-ish....

 

[screenman]

Do you mean smallest to smallest, if yes then do not do it.

 

[fossyant]

You shouldent run chains at a bad angle like that. Big to big and small to small. Usually the last three are a no no.

 

[neil16377]

Yes. Smallest to smallest.
Even with Trim the chain still rattles on the smallest FRONT ring

 

[neil16377]

I knew that Big to Big was a NO NO. But didn't realise that small to small was an issue!!

 

[JMAG]

Whilst it's not advisable to cross chain, it's your bike so knock yourself out. Is it rubbing throughout the whole pedal cycle or just part of it. If part, your chainset might be bent. Otherwise, your chainline might be off a bit i.e. chainset is a bit too close to the frame causing a slightly exaggerated angle. It's not helped by having the widest cassette available (11 speed).

 

[DEFENDER01]

Chain line
If your bike is correctly set up, then when you are in the middle chainring (if you have three) and the middle sprocket of the rear wheel, the chain will run in a perfect straight line, parallel with the wheels and direction of the bike. As you use different combinations of gears, the chain will flex from side to side to accommodate the difference between the lateral positions of the front and rear cogs on which it is travelling. This angled line that the chain follows is known as the chain line.

Many riders are unaware that certain combinations of gears should not be used. In the most extreme combinations of gears - either running the chain on the largest chainring and the largest sprockets on the rear wheel, or the smallest chainring and smallest sprockets - the chain line will become very severe. This results in extremely poor operation, rapidly increased component wear and potentially the chain coming off and jamming, even on an otherwise correctly set-up and maintained bike. By not attempting to select these gear combinations, you will enjoy improved performance, greater reliability and increased component and, in particular, transmission life.

The following three images illustrate normal variations in chainline, demonstrated on a bike with a single front chainring. Click on the images for larger versions and further detail.




The next three images show the effect on the chainline of selecting the most extreme combination of gears. As before, you can click on the images for larger versions and further detail.

 

[neil16377]

Thank you for such a detailed response...that explains everything I needed to know.., LEGEND!!

 

[DEFENDER01]

Thank you for such a detailed response...that explains everything I needed to know.., LEGEND!!

Your very welcome.
Sort of makes sense when you see it in pictures.

 

[Crandoggler]

I can use every gear in any combination. Then again I have a SRAM yaw front deraillerur. Suppose it induces chain wear to a degree, but never mind.

 

[DEFENDER01]

I can use every gear in any combination. Then again I have a SRAM yaw front deraillerur. Suppose it induces chain wear to a degree, but never mind.

Yes it will put extra strain on the sprockets and chain no matter what make of gear change you have.
I have SRAM as i prefer them but do try to avoid those combinations { mostly i leave the chain in the center crank sprocket so the problem doesn't arise.}

 

[raleighnut]

I can use every gear in any combination. Then again I have a SRAM yaw front deraillerur. Suppose it induces chain wear to a degree, but never mind.

It increases chain wear a lot, probably halves the life due to the increased angle that the bushes are forced into as they enter and exit the sprocket teeth but its your bike so do what you want to it.

 

[adscrim]

Hi.
Wondering if anyone can help me out, I have a bike with ultegra 6800 52-36. 11-28 cassette.
The crank is a FSA si

Everything is new on the groupset- the hanger is straight .
But I get chain rub on the highest gears and the lowest crank cog 36t. Chain hitting the crank !!
There is no apparent Rub on the front derailleur at all,

What am I missing?? Cheers

Chain angles aside, you should not be able to get into a position where the crank arm is hitting the chain (or vice versa) during 'normal' operation - ie in any front/rear combination. I'd find the reason for that as soon as possible.

 

[Crandoggler]

Indeed. They're useable, but rarely used.