Put a pair of Road 5s on my NT this weekend to replace the BT-023s that were on it. Weight rating on the sidewall of the 5s were identical to the BT-023s, so there shouldn't be any issue at all. Hoping these will give me more confidence in the front end and help with the rear suspension harshness. Thinking about new springs as well this year but I'm going to put some miles on the tires before I jump into that.
I believe many here find the NT rear suspension fine but I find mine harsh also.
Part of it for me is 1. I'm not too heavy yet (but getting there). 2. I don't load it up with much extra weight.
3. I sit pretty far forward on the seat.
Several here have swapped out the spring including me. For me it helped some. If you decide to replace the spring the difficult part is picking the right spring rate. There is not as much history/knowledge with the NT as compared to more populated bikes. There is probably more knowledge on this site than most places (maybe not Europe since it has been there a while).
I just ordered a set of Road 5s. I've got over 12,000 on the PR4s I bought just before I hit the deer in '16, and I'm planning to ride to WV for the NT Rally there in May and then, on Memorial Day weekend, do Eric Trow's Stayin'Safe riding training two days plus an extra "free" day on Monday. The current PR4s still look pretty good, but I'm guessing that I'll want newer rubber before I head out on that trip.