Foams, I can't help too much with... but I think 26mm wide may be the limit due to the wheels hitting the kunckles. This is because the front knuckles (and the cer in general) is designed for rubbers, which the most common size is 24mm.
From what I recall, there are a few things you can do to help.
1) run the 6mm silver wheel hexes, with some spacers to space out the wheels from the knuckles. Just beware, this could take you over the 190mm width, but is the easiest to do
2) Run HPI/HB Cyclone front knuckles. Effectively you can run these as a direct replacement, and all known foams have enough clearance.
You need the front knuckles, 4 x 1050 bearings, and some HPI/HB non-MIP stlye wheel axles. Fit them together (the tamiya dogbones are a direct fit into thoose axles), replace the current front knuckles, put a 1mm spacer between the C-hub and the top of the HPI knuckle, and your good to go
It's a bit more of an expensive route... but it seems a lot of foam tyre racers use this method with good success.
3)Cut down your wheels to fit... or run thinner fronts.
HiH
Ed