Our new Windjammer came with aluminum wheels from Lionshead. I replaced the CastlRock tires with GY Endurance and contacted Lionshead through their webpage and asked about their PSI rating. Here is their response:
The wheels do not have a PSI rating, they have a load carrying capacity. The valve stem in the wheel would have a PSI rating, if you are looking to upgrade to a tire with a higher PSI rating, you would need to be sure that the valve stem is also replaced with a valve stem that meets the requirements of the higher PSI of the tire upgrade.
They installed metal valve stems with the new tires, and I have a lot more peace of mind now than I did with the CastleRocks.