Crank Flex?

Bluey_27 said:

heres the deal. The chain rubs on the FD when i sprint in my biggest gears (50x13 and 50x14). I've set the limit screws as far as it'll go without overshifting and it still rubs. The cranks are just the crapy OEM pinarello MOST ones (square taper BB). Would this be the cranks and is there anything i can do?
BTW Im running Ultegra 10speed FD with the MOST compact cranks.
Thanks alot

It could well be chainring flex, not crank flex. Chainstay flex will also move the chain, and BB flex will move the cranks. I put my money on chainrings (but FSA (makers of the MOST cranks) cranks do tend to be on the flexy side)

Crank flex shouldn't translate movements to the chain/FD interface unless the BB axle and chainrings are also being flexed by your power.

Is it possible that there's wear in your BB bearing and the axle is tumbling around wrt the horizontal axis of BB?

The frame is what flexes.
Happens to alot of bikes. FRAME !

sogood said:

Is it possible that there's wear in your BB bearing and the axle is tumbling around wrt the horizontal axis of BB?

Yes, check to see if your BB spindle floating (moving left-and-right) isn't the culprit to your problems ... grab your crank when you are standing next to the bike, and see if you can move the crank to the left-and-right.

hmmmm.... everything seems solid and tight so i'll ring the bike shop tomorrow, see what they can come up with.
thanks

Bluey_27 said:

hmmmm.... everything seems solid and tight so i'll ring the bike shop tomorrow, see what they can come up with.
thanks

You know, the MOST bottom bracket is supposed to be super-stiff; so, frame flex (even if you are using the "adapter" to allow a normal BB) should be negligible ...

I've looked at the frame that I have which has the worst-combination of components -- a mismatched 8-speed front derailleur (i.e., wider cage, so it has to move a little further over to shift the chain in both directions) with a 9-speed chain on a 9-speed drivetrain (FSA ROAD crank) ...

When the chain is on the outer ring AND I am looking down the outer plate from above, the outer plate is flush with the "safety" pin on the ring which on the particular chainring extends about halfway to the crank arm's back side. There must be ~5mm (just eyeballing it) between the outer plate and the backside of the driveside crankarm when the front derailleur is at its maximum outer position.

This raises two questions about your bike's configuration:

• what chain are you using?
  
• what front derailleur are you using?
  

Is it possible that you are using a 10-speed Shimano chain in anything other than a 10-speed Shimano drivetrain?

OR, is it possible that if the drivetrain is a 10-speed Shimano that you are using the wrong front derailleur -- a 6500 instead of a 6600, for example?

Of course, there are OTHER wrong combinations you could be using!

A 10-speed Shimano chain with a 10-speed Campagnolo drivetrain should also be avoided!