Choosing sizes was not straightforward because Heidenau doesn't make a direct replacement for the OE Trailwing size. The closest match I found is a 90/90-21 for the front, and 4.00-18 for the rear. Just to confuse matters, some dealers don't have the K60 Scout model in stock. They only offer the original K60 (non-Scout) version which I believe comes in a different size range. Otherwise, the main difference I could see between the versions is that the Scout incorporates more of a central ridge in the tread. But just to confuse matters further, Heidenau changes the tread pattern depending on size! So all I can say is that I ordered the sizes above from A Vicious Cycle and they fit just fine on my WR250R. You can see from the photo just how different the shape and size of the rear tire is compared to the (worn) Trailwing!
Dismounting the Trailwings was epic, as the sweat-spotted floor attests. Wear gloves if you value your knuckles. Mounting the K60's was relatively straightforward, and the rear was surprisingly much faster than the front. Baby powder make a great mounting lubricant: apply it liberally to the inside of the tire and all around the tubes and rim. This is an old cycling trick. It creates a lot less mess than using soapy water, and it allows the inner tube to settle into the tire easily. It's slippery enough that you can seat the bead with a hand pump. Any excess will wash off. Bonus is your bike smells baby-fresh when you're done.
Note that according to Heidenau, two red dots on the sidewall indicates the slightly heavier part of the tire. (If there's just one red dot, it's even heavier which seems counter-intuitive.) I positioned the dots opposite from the valve stem and this rode fine with no excessive vibration.
So how do they feel? An initial ride on a mix of town asphalt and hard-packed gravel roads showed a responsive, stable, and predictable feel. Particularly on loose gravel and uneven surfaces, I found the Scouts tracked much better and didn't wash out or skip around compared to the TW's. Cornering felt good, and the more rounded tire profile gave a faster turn-in. I'll have to get used to that. Overall my WR feels like a new bike. The larger diameter rubber may be an important factor in that regard: it smooths acceleration and bumps without giving a noticeable loss of zip--much like moving to a 29er mountain bike. I don't expect stellar mud performance, but that's not the goal anyway. Gravel performance is probably the most important factor in my riding.
I'm curious to see how these tires perform once they've broken in a bit. Stay tuned for an update.