Not sure what the proper name of these types of weights are. I want to say octagonal or hex plates but they have more than eight sides... hopefully that gives you a picture of what type I'm talking about.
Do you have a higher probability of "tweaking" your back with these types of plates when doing deadlifts?
I try and get them locked in place on the bar but they always have a tendency of moving. Someone I spoke to said a buddy of his injured his back doing deadlifts with these types of weights -- and I can see why since they have a tendency of shifting when you place the bar back into starting position.
I know they have bumpers for these to make the plates round, the gym I'm going to does not have them. Do all you need is two bumpers (one for each side -- it will lift the weights slightly off the ground, correct?) or do I need one for each individual plate?