My first test was to jack the van up so the wheel could spin freely and then use one of them to hold the tire, while loosening the nuts. Not only did I have to push it in, I had to hold it with my foot to keep it from falling out. I've also tried putting both under the front wheels and letting the van roll over them. Because they are ductile and hard, they do not adhere well, especially to concrete. The van was not on the slope, it was only jacked up at one end.