Hi Harvz, and welcome to TGMF
I'll be honest and say I haven't actually got around to measuring the bore size in those wheels. I should imaging they will be of a size which would take proper bearings, but like I said I've not investigated this yet, they look pretty big though. I have one sitting there waiting for new bushes now, so in the morning I'll have a measure up and report back.
Why the heck they designed it like this is beyond me, they are seriously rubbish for such an expensive mower.
There's a couple of other things that irritate me about these machines, one being the handles, the always flair out at the bottoms and then won't locate securely.
And on the latest engines those three studs that hold the tank and recoil, always come out with the nuts, and the hex is now hidden in the plastic cowl so you can't get hold of it.
The power of dreams my ar$e. lol..