Originally Posted by thirdin77

My excuse for wanting a 19T middle cog is laziness.

On my cross bike, I run a low-pressure 700x32 tire which means more friction than a high-pressure road 700x23-28 tire and if I use a road 50/39/30 triple with a 12-25 cassette which will have a 17T middle cog, I'll get a 61" gear when I"m in my middle ring/middle cog. That's too big for when I want to go for an easier, slower ride and try to stay in my middle ring/middle cog.

The 19T middle cog would let me have a 55" gear in my middle ring/middle cog. Perfect for cruising.

I place so much emphasis on the middle/middle combination because if the middle/middle is my cruising gear, I will have access to more of my lower gears/bigger cogs than if I was cruising in my second to middle cog. With most 12-25 cassettes, the 19T would be my second to middle cog.

This can be useful as when I'm tired and in a headwind and I want to access more lower gears from my middle ring, I'll have about four lower gears to drop into rather than three if my 19T was my second to middle. This also means that I won't as easily find myself in my biggest or second to biggest cog.

So it's laziness and idiosyncracy.