÷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.

Well, I picked up the bike with the new Bridgestone Battlecruiser H50 tires on it the night before last. It was raining on the way home and I was taking it easy since they are new and probably coated with silicone but they seemed to do well in the rain. So far I have out about 500 miles on them. I took them over some really challenging roads here in the Western Carolina mountains. The Blue Ridge parkway, The Rattler (209), and The Tail of the Dragon (US129).
I am absolutely thrilled and very impressed with the New Bridgestone Battlecruiser H50 tires on my 2014 Valkyrie. They have transformed the way this bike rides and handles. Much improved over the Metzler 880's that were on the bike. The ride is much more controlled and less twitchy. Side to side transition going around corners is much smoother and easier than with the 880's and it seems to hold the line through the corners at both high and low speed with much more ease and confidence. High speed stability is greatly improved. I have Bridgestones on my Goldwing F6B (they are the factory recommended tire). I have had a lot of different tires on that bike, Dunlop Elite (3 and 4), and others and I keep going back to the Bridgestones, they are great value for the money.
The mechanic that installed the new Bridgestones on the Valkyrie was worried that the 60 aspect sidewall verses the 55 would be too tall and would be too close to the front of the swing arm but after riding hard yesterday and with the tire temps close to 100 degrees ( I have FOBO 2 sensors on the Valkyrie) there was still almost 3/4 inch between the tire and front of the swing arm.
In conclusion, I would recommend the Bridgestones for your Valkyrie. I will report back as to how they hold up mileage wise and as I spend more time in the rain. We are here in the mountains till November and I average about 500 miles a week on this bike so I should know by the end of fall how they hold up.

I see mixed availability of radial tires. from my ignorance on tire construction, I would assume that bias-ply tires would have gone the way of the Dodo by now; apparently not! What is the current thought on mixing bias ply and radial tires?

I've been running a bias Michelin Commander II 130/60 19 for over 15,000 miles now, still looks good and greatly outperformed the stock Dunlop radial. It eats up those construction seams like they're not even there, while the stock Dunlop tracked on every road imperfection. That said, when it comes time, just out of curiosity, I'll be trying what several others have been happy with, a Michelin Commander III 120/70Radial.

Here's a good article on that subject with two points I remember is that at least one Harley model that came that way stock, and just don't put a radial on front and bias on the back.

https://www.revzilla.com/common-trea...d-radial-tires

Here's another good tire article:
https://www.baggersmag.com/best-long...-touring-tires

Let us know what you decide on and how it turns out!

Is that tire choice wider and lower profile?

200/50 would be 20 mm wider and 1 mm taller (radius, or 2 mm diameter) than a 180/55.