[Lowfer] Casters for equipment?

[KD7JYK DM09]

I have a heavy piece of equipment in need of wheels.  I've been looking at 
6" cast steel casters rated at 1,400# each.  Two fixed, two pivoting with 
brakes.  This item will be in a room with a concrete floor.  I find the 
casters come with either flat wheels, or a V-groove in the center of the 
wheel around the circumference.  I've seached online and not been able to 
find a reason, or advantage of one or the other.  What is the purpose of 
steel wheels of the same design, one with a groove, one without?

Thanks.

Kurt