New Rotor Crankset with Q rings

paulieb2006

Folks I got Rotor 3D+ cranks fitted to my bike earlier today. They are complete with Q rings which are 52 39 I think. Now they run perfect on the inside ring until you go into the 11 on the back. Then the chain is getting caught on the pin on the inside of the outer chainring and jumping it quite badly.
A mate of mine has a similar problem but he started off with compact Q rings and upgraded the outer ring to the 52 so he just thought that it might be cause he has compact on the inside and standard on the outside.
Has anyone any idea for me?

StillGoing

I don't have a pin on the inside of my Aero rings? The only pins are on the outside to prevent the chain dropping between the crank arm and the chain ring on the outside. You are however doing the classic cross chaining to the extremes going from inside ring to 11 sprocket on the cassette so there is likely to be some chain rub.

DKay

You shouldn't ever be using the 39 11t combination anyway, so it's academic.

paulieb2006

100% its bad form to use those gears but this is more than just that. I had a Ultegra 6700 crank on it up till today and sure the chain would rub on the inside of the Front D but nothing like what is happening now. I am just worried that it could do damage to the chain or rings or even come off if I did drop into that gear at some stage. Its an expensive of kit also and I want it to be right!

ElectronShepherd

DKay wrote:

You shouldn't ever be using the 39 11t combination anyway, so it's academic.

But if the gears are set up correctly, you should be able to use all combinations without the chain rubbing on either other chainrings or the front derailleur (assuming its trimmed), so the fact that the OP can't indicates that something isn't right.

When you say it's hitting the pin, how big is this pin? Do you mean the little pins that help the shifting, and are about 1mm proud of the ring itself, or the big ones about 5mm tall and about 3mm across? The big ones are to stop the chain dropping between the crank and the chainring, and should be on the outside, with one tucked behind the crank arm.

Is it as simple as the big chainring is simply fitted the wrong way round? (i.e. the inside face is on the outside)

paulieb2006

from what I can make out its the one that sits about 1mm from the inside of the ring! I t looks to be on right but to be honest its in the LBS and cant check it till tomorrow.

John.T

This is normal for non round rings. When your crank is at 3 o clock the effective size of the inner ring is less than a round 39, probably close to a 36. The chain is trying to clear the outer ring which is lined up so the chain is passing it's biggest size, probably around 55. If you think Q rings are bad try using Q-XL or Osymetric. Good to ride but forget cross chaining on the little ring.