Thought I would tell you my car ramp story from a few years back.
I went and invested in two pairs of car ramps to make under-car work easier, for example transmission service as the vehicle remains level. Used them a few times and they were absolutely brilliant. Then I noticed that they were taking chunks out of my garage floor every time I used them, due to some sharp edges. So like a true pro I got out the trusty grinder and took those sharp edges right off (which I suspect were meant to be there).
So I go to use them next time. Vehicle is half way up the ramps when one of the front ones takes off like an ICBM and smacks into the rear garage wall loud enough to have my child bride come running into the garage to ask what the @#$%^& is going on. The vehicle is now teetering on a crazy angle as I try to keep a straight face and tell her it's meant to be like that.
So, solution was that I always have the vehicle in 4WD when I use them. They truly are great to use,... just don't remove the sharp edges.
Andrew.
(For those that don't know, the term 'child bride' is humorous sarcasm, I don't want anyone thinking I'm a weirdo).