÷Time to replace the rear tire and thinking of going one size narrower 170/60/ZR17 to match the popular one size narrower front tire option 120/70/ZR19. What do you think anybody do this yet? The rear rim is 5.5" wide correct? A 170 should work on that width rim.

Yeah a 170 should fit just fine

I used Avon Cobra Chrome
200/50 17 and 130/60 19
Fits fine and handles great, also the grip if perfect, dry or wet. Really like it.
Speedo shows almost 1 to 1 with GPS navigator.

Ended up putting a factory 180/55/17 ZR Continental Conti Motion. $101 from American Motorcycle Tire. I'll let you know how it feels after I get some miles on it.

I just ordered a set of Bridgestone Battlecruise H50 tires for my 2014 Valkyrie. The sizes are 130/60-19 for the front and 180/60-17. They cost 277$ for the two of them from Bike Bandit. They are designed to be run on heavy V-twin cruisers and are pretty close to the stock sizes and the price is right.
I currently have Metzler 880's on the front and rear. I have not been really happy with them. Been through 2 rear Metzlers in the last 3K miles. They were very noisy, fairly hard riding and I had a flat on the first one and then a blowout on the 2nd one.
They will be mounting them next week when I get back to NC.
I will give a report when I get some miles on them as to how they ride and handle.