tl;dr: Put a new front wheel on and new front/rear tires, now I'm getting low speed (~20mph) vibrations. Help please?
I have a '15 WRR. I got it with like-new D606 tires mounted on it, rode it like that for about 500 miles, then decided to get a more street biased tire for commuting. I also moved to a new 19" front wheel to compromise closer to a supermoto setup. The front wheel is a Warp 9, 2.15"x19" rim. The tires are Mitas E-07s, 100/90-19 front and 120/80-18 rear.
I just went out for my first ride with the new wheel/tires today, probably hit no faster than 40mph, but noticed a very significant vibration (maybe oscillation is a better word to describe it). It seems to be worst around 20-25 mph. I'm used to the vibration of the engine; this is a different, more violent, slower frequency vibration. It feels like what I would imagine an unbalanced wheel would feel like, but as far as I can tell I balanced both wheels (with the tires on) dead-on. The tires both look well seated to me. Any ideas what might be causing this?