I don't think it's the size of the wheels there is something else causing the problem. I use small swivel wheels off an office chair on a 2x3 foot dolly and can easily move a car engine around the garage.
On what surface? On smooth concrete 3" should be good, the rougher or softer the surface the bigger the wheels need to be.The 3 inch wheels were just too small could not move easily. I'll have to take some photos.