Thanks to every body for their insight! I’m repurposing a Specialized Tri Cross Comp. I was trying to get it to where I can spin up a rather lengthy and steep hill, which would allow me to commute.

I was already planning to swap out my small ring at the same time I changed the cassette. It has a 48/38 FSA crank, 110 BCD. I want to swap out the small ring to get it to a 48/34. It looks doable from what I can see for only the cost of the ring, maybe $40. I will start here.

For the cassette I wanted to change from my current 12/27 to the 11/34. I was only thinking about the splines, like if this cassette would fit the hub, and I forgot to take into account the contact with the rear derailleur. The RD is a short cage like on a road bike, its a Shimano 105 9spd.

So you think if I choose to change the cassette (About $50), then I also must either: change to a long cage RD, maybe $40-80, or try the wolf tooth RoadLink, for about $30 and keep my existing RD.

Since I also didn’t want to spend a bunch on this I might start with the small ring and see how much it helps.