Shimano 105 LH shifter

[Fattman]

To follow up... have just checked Zinn... he has a very long section on chainline and the problems it can cause with dropping off and chain rub. He blames it largely on an incorrect bottom bracket width setting the chainrings out (not likely as a problem if running with a Hollowtech BB) - though it could be frame misalignment. I guess it might happen if the sprockets are off - e.g. if missing (or excessive) shims?

Anyways, to check apparently either (a) simply put a long rigid straightedge between the chainrings and see where it lines up at the back or ( complicatedly measure loads of stuff like wot he shows in his pictures in Zinn and the Art of Road Bike Maintenance.

 

[andy_wrx]

very helpful indeed; and it suggests that if using it for a double it should be used with the 1st and 2nd click NOT the 2nd and 3rd click, as many have suggested

Indeed. When I bust my first one of these, Evans hadn't left that sticker on, so they gave me a new one. If you can avoid over-shifting then I guess it's the way to go - just seems weird that a fantastic engineering gang like Shimano would effectively design a mode of failure into the component.

It's a pretty stark warning that if you use them on a double and you try to shift into that third position then you will knacker them - bigtime !

But going back to my original answer, if that's the way they fail, by setting them up to use positions 1 & 2 and locking-out 3 using the high-stop on the front mech, but they fail in a spectacular and fatal manner if you do happen to try to select position 3, then if instead you were to set them up to use positions 2 & 3 [and assuming of course it works !] then whilst you can't lock-out position 1 but if you inadvertently select it all you'll do is just uselessly slacken an already slack cable a bit more and it'll do no harm.