No they are not, at least as pictured. Andy said and I agree, if another car say ran into the the car, it could rotate the wheels and allow it to roll off these stands, as nothing(?) is to prevent the wheel hubs from rotating. If you mount casters to the bottom, and do not significantly extend the base ( which the small base being the original benefit to most in the first place?), having a a moving car on casters with all its mass, only needs a caster to stick on something, a crack, a 1/4" nut, cable, etc, and the car could easily roll the wheel hubs and off the stands. Likely, probably not, would some one be under a rolling car, again not likely, but the "stuck" caster should be considered, IMO.