What is the maximum incline for a 4X4 trail ?

Question

I mean the maximum practical incline for a road that will be used daily. Ice is not a factor. What is this in degrees of incline ?

Answer 1

The mathematical maximum incline a 4 x 4 can handle is determined by the ratio of the distance from its center-of-gravity to its rear axle and the height of the CG above the bottom of its tires.
Let
d = distance from CG to rear axle and
h = height of CG above ground on the level.
Then
slope (in %) = 100*d/h
and
angle of slope = tan^-1(d/h)

At this slope, though, a single pebble or stopping and trying to restart will cause your 4 x 4 to roll. I recommend a generous safety factor.