I've developed an interest in building up some form of this beast (referenced as a "Supermotard". Built by Amaro). I would like to tone it down a bit...I would essentially like track geometry for sharp handling but a fat tire for making quick work of the crater-laden surfaces called roads in New Orleans. Some roads are fine, which leads me away from a mtb style bike.

What SS/FG/Track frames would allow for a fixed gear, 26" wheel with fat (>2.0") slick tires?

Surly? The Karate Monkey frame would be a good candidate for something like that.

I would think that the Steamroller would suit your needs pretty well.

Check out this this thread. These are all off road beasts, but they're pretty awesome.

https://forums.mtbr.com/showthread.ph...hlight=monster

Shoot, I just use my fixed gear Monocog 29er for that purpose. Schwalbe big apple 2.35" tires laugh at potholes. A fixed Surly Pugsly would frighten children. I like your style. That supermotard is sweet. I turned my KHS witch doctor into a supermotard inspired urban assault vehicle.

The Surly frames seem to be a good choice. Since it is not a conventional choice, asking if a 26" x FAT slick will fit in a 700c frame is probably not an easy question to answer.

The 29'r option is another thought, although I was trying to favor the use of 26" wheels. I have an assortment of spare 26"/mtb stuff that I would love to put into service.

Any other ideas/experiences? There are probably many ways to develop the "Urban Assault Vehicle" concept.

A friend of mine runs a Singlespeed Surly Karate Monkey with 29" wheels, drops, and disc brakes. If I had the money or even the need to build another singlespeed bike, this would be it. Its a great bike for around the city, up and down curbs, and crossing it through the grass and trails.

What about the Surly 1x1 if you're set on 26" wheels?

This thing is hideous but does have very large slick tires.

https://www.surlybikes.com/1X1_ltd.html

Klein Rascal or Fervor is right up your alley

I'm in the same position as you. There are plenty of MTB that will take fat tires, but nearly all of them have 71/73 head/seat tube angles, or slacker. Very few mfgs. are building road bikes that will take a 50mm tire.

700x50mm Big Apples will fit in a surly cross-check.

The closest thing that I have found is Rawland Cycles, which are designed for 650b wheels. The next frameset will have disc brake mounts, so it could use 26" wheels instead.

Another option is to find a MTB frame with a high bottom bracket that is designed for a 100mm fork, and use a shorter rigid fork. But that requires a solid knowledge of frame geometry to work right.

I think what might work better would be a 24" bmx bike with 20" wheels and beefy street tires.

Having a full size mtb riser bar with cross bar and pad is a must, screw those drops

I'll be doing a build like this soon.

The problem with the manufacturers' clearance claims is they're mostly for 700c tires where they'll hit the bottom of the fork before the sides or the brake bridge before the seat/chainstays. Nobody is really measuring for maximum width on a smaller rim.

My plan is get the wheels made first (MTB rims laced to "track" hubs with 2.35" Fat Franks) then just keep trying frames until I find one that works. I've got friend who'll let me mock up his Jamie Roy but I'd love to see it work on a Steamroller so I may beg around locally until I can find one to test.

Measure it up dude, you'll find that 2.35" mtb tires have pretty much the same diameter as a 700x28. I don't think there is a production frame out there that has those kind of clearances with anything close to track geometry.
An older touring frame w/long chainstays will be your best bet, otherwise, the chainstays will have to be curved to fit the tire....hmmm, there might be a cross frame out there like that, but then it's doubtful it will have horizontal dropouts

Well Surly says the Steamroller clears 38mm tires with fenders so the height won't be a problem. And the widest part of a 26 inch tire is closer to the hub, where the stays and fork are wider.

I could measure various framesets but if I have the wheels anyway I'd rather just slide them on and see what's what.

If anyone is going to pull it off, it's going to be a steamroller. I've seen 29" Bontrager XDX 1.9" tires fit in those things.