I do not know how they constructed the Katy Trail but I think they might have put some cement into the mix. I found it to be much harder than other rail trails I have ridden, almost like concrete. There were a few exceptions on the eastern end, but overall it was almost like a highway.

Above in post 19 I included two photos of C&O trail after rain. I tried to attach a photo of Katy trail here but the system is not cooperating.

LOL. The Katy is crushed limestone, which, if you heat it, crush it, and mix it with water, would be concrete. The small aggregate that DNR uses has a lot of limestone dust in it, which compacts very well, leading to a very hard surface when it is dry. When it rains, though, it soaks up the water and can be pretty soggy for a few hours. It is also prone to washouts in heavy rains and canyon-like cracks in droughts.

The point is, if you aren't riding on actual concrete/asphalt pavement, go as wide as you can for a comfortable ride.

I've done crushed stone on 28s, armadillos, it was fine but I wouldn't do it on 23s

I just did the Katy end-to-end with a group in mid-June. One guy did it on a fat tire bike with 26" x 4.5" tires. While he said the ride was comfortable, it was just a little overkill!