The 22.5" wheel that fits a 52 6400 is only 5.25" wide, unless you've found a wheel I'm not familiar with.
The narrow rim width is your limiting factor on picking tire size.
As crenwelge explains, 9R22.5 is the size you'd like to run.
If you look up specs for a 9R22.5 tire they will list a recommended or allowable rim width, 6" or one size wider. I haven't looked up similar metric 22.5 tires but doubt any with a suitable overall diameter fit anything narrower than 6", if even recommended for a 6" rim.
Back to the 9R22.5
You have 5.25" rim, 9R22.5 tire needs a 6" rim by the book, you can actually fit it on a 5.25" rim, it will work, it's not technically recommended, but you don't really have any other options. I've run this combo with good results thus far.
Those 22.5x5.25" rims used 8x22.5 and 7x22.5 tires which I believe have been gone and obsolete for many decades.
