This is a bit more complex than it sounds. I had the opposite experience to organ donors. I had a set of wheels that were solid, thinner and slightly smaller diameter than the real robbie wheels.
I found them to be a lot more difficult to manage, especially on rougher ashphalt. They tended to jam more in the ruts and on loose bits of gravel etc. Part of this might have been due to the slightly smaller diameter so if you continue down that path I would suggest going as big diameter as you can still get to fit in the wheel lugs.
The other problem I had was the wheels were put onto a normal set of wheel handles/axle. After about a year the base of the short stub axle (that goes into the skid bracket) broke along the 45 degree weld while I was moving the machine. Very inconvenient as it was stuck half in / half out of the hangar. I had it welded up and it broke again. Had it rewelded and a solid rod fitted inside with the broken bit as a sleeve. Then the other wheel broke in the same place. The welder fixed it and suggested the cause was with the solid tyres the jarring of rough ashphalt was transmitted into the hub of the wheel and it eventually gave way. The pneumatic tyres (the proper ones) absorbed a lot of the jarring as it was pushed around over the rougher asphalt.
The solid-rod fix seemed to work so you may think about a pre-emptive fix.
I manufactured a front set of wheels on an cross bar that allowed me to spread the weight on 4 wheels and that made it a lot easier. (From an idea I saw for a similar system on a Squirrel in a magazine) Was easy to make and meant I could easily push it around myself and roughness of the ground made no difference.
Diagram attached - sorry about the quality of my art work
Works well even with solid wheels. Allows you to push or pull from any position without a second person - tail boom, engine frame or even backwards from on the nose.
The rope loop tied to the cross bar allows you to pull it into place while standing at the tail. You pull down on the tail and lift the skid toes then pull the wheels into position. Make the rope the right length to hang on the stinger so you don't have to hold the rope yourself.
The wooden "U" shaped blocks and strips of velcro are held on with plastic zip ties. The wooden blocks fit the skids in and are shaped to stop the skids slipping off as you turn. The velcro strips keep the skids in place while you are manouvring.
I will say that I agree with organ donor about the lack of inconvenient flat tyres. Never had one in five years.
