Reason I don't like them is if your not on a smooth surface such as tarmac at the track, since they have a flat base they don't sit 100% flat.
Main reason I didnt like them was because if I lift the front of the car and support it with those then lift the back, when you start lifting the back they would start to lean. First time I used them the car almost fell off. They work fine if you use them to support something that won't be moving, such as the back once the front is already up. I prefer my jack stands with the 4 legs much better.
Bookmarks