Recycling tyres
That's not strictly true. There is a very lucrative industry in shredding old tyres, containerising them and then selling / laying them in vast amounts to cover the courses used train racehorses and such like. I used to rent a house on a training farm in West Sussex and the suppliers were always in laying tons of the stuff in all weathers.
Not saying all tyres go this way but it takes a fuckton of them to be shredded to a smallish size to cover a 2 mile course to a depth of 3 inches.