Last month two friends and I distributed 60 tons of hardcore onto the dirt track. That's 20 tons each! Not having done this before, 60 tons sounded like an awful lot. But when you look at it, it just looks like a big mound, not very substantial.
That said, it took the three of us a bit less than 2 days with digger and dumper to spread it out. The theory was to create two small tracks for car tyres and leave the middle uncovered so that grass would grow, but the way the digger spread it out, we ended up with hardcore all the way across. That meant that we didn't cover the entire length of the track.
After the first rains, some of the mud underneath began to show through, so I think we'll get grass up the middle easily enough. It also means we'll probably need more stones....
With hindsight I wonder if it might have been better NOT to have scraped off the grass, and just have created a track by continuously driving up and down the hill?!