Not fixed, but I ride my SS Cross Check - drop bar, currently 34x18, Nano 40s - quite a bit on singletrack and fire roads. In fact, it sees very little pavement. I use my geared gravel bike more often simply because it's so steep around here, but man, every time I come back from shredding on the SS, I am always very stoked. I love it.
Funny thing, the other day I was riding it on a trail that's usually frequented by MTB's, w rock gardens, etc. I had stopped to chill, and a guy on a full squish MTB pulled up, looked at my rig and said "Why?". Cracked me up.