If you are talking clinchers, they fit. I'm running 23mm GP 4000s on 7.8s without issue. I started with 25mm's but had issues with frame rubbing.

clinchers...thanks for confirming.

Make sure that the first bead is already in the middle of the rim (the valley of the U, if you were to look at them head on), before you try stretching the other bead over. You’ll find some clinchers fit better than others but nearly all will fit with the right technique or prep. I’d recommend switching to the Silca rim tape and perhaps prestretching the tire you’re having trouble with on a narrower rim or leaving it in the sun for a bit. There’s also a KoolStop bead jack that Thomas Gerlach recommends that I’ve had success with.

i've never had an issue getting a 23mm or 25mm tire over any clincher until this one. the one side of the wheel that is already on the rim is in the middle of the U (if not even closer to the other side of the wheel) and still. i tried inflating the tub partially over night to straighten out the tire - it was a bit mangled, but nothing. using the plastic tire levers wouldn't help.

Are both beads in the center of the rim?

If i remember right, Jim at ero strongly recommends 25's with those wheels for optimal aero