Browsing through Cooper's D11 thread for that Clinometer App he mentioned, I downloaded it to my IPhone & then checked the current incline that I have, it varies between 17 & 20 degrees. The loaded B50 travels up without slippage (barely) with dirt rolling off the back. And for a brief period with pup in tow as well, the B50 had lots of wheel slippage, chewing up the incline... so 20° is too much.
I have about 20 cu yd or more to come out of the basement yet & using this exit into the shop is more appealing than the narrow spiral ramp that exited south side of house.
Plus the challenge of carving that road out of the basement would be fun too.