Let's assume your tires can handle 1G in either cornering or braking. You can brake at 1G, corner at 1G, or do both at once at the square root of 1/2 or 0.7G in each direction.
It's the same patch of rubber pushing on the road, I'd say that the maximum length of the force vector is 1G no matter the direction. The rest is just vector addition. (Ignoring effects like the deformation from the sidewall and the action of the belts due to their orientation versus tire force.) Your math checks out in my head! -- Jim
