I've used them on some of my cars through out the years, as far as safety, I never had an incident with them braking or shearing of the studs (I split an axle once, but the spacer was fine!). But as far as clearance, It was never an issue, because I never used them on the front, only in the rear with the car jacked high to clear the slicks. And the cars had solid axles not independent suspension like are Mark have.