Originally Posted by
JohnDThompson
They are necessary when using indexed front shifting with a derailleur and shifter that don't allow trimming to eliminate scraping the chain on the derailleur cage. To make indexed front shifting idiot-proof, the shifter does not allow trimming; you're either in one gear or the other. To eliminate scraping, the derailleur cage is made wider to provide more clearance without scraping. But this degrades shifting efficiency, so pins and ramps are added to the chainrings to facilitate shifting even with a wide derailleur cage.
+1 I don't do index shifting so trimming is easy. Many of my FDs are the old, narrow ones. I further narrow the backs of the cages by removing the bushing and replacing it with a shorter stack of very small washers. Also tweak the angle to slightly inboard at the back. Often bend the front of the outer plate in. (All this done with the old SunTours.) A plus about no index - I can leave the cable quite loose to simplify loosening the clamp and twisting to dial in the angle. Leave the chain in the big ring with the lever thrown forward - DT levers.)
I want my FDs to shift reliably from the smaller cogs in back, when I am still rolling fast up that hill. Then, little speed lost and I get to shift just in back as the hill steepens and I slow. Yes, old racer thinking but also using inertia to make the hill easier. As an aging cyclist, why wouldn't I want that?