On Tuesday, October 28, 2014 4:42:27 PM UTC-7, wrote:

I google "hand truck proper tire pressure", and get a thousand
hits with out a single figure in PSI.

http://www.csttires.com/int/lawn-and-garden

MTD said 10-14 PSI was right for its riding mowers. I doubt any
tires can't take that pressure.

One day, somebody will invent a real search engine. Meanwhile:

Don't include unnecessary words, like "proper".

Try "hand cart", "lawnmower", or "garden" instead of "hand truck".

Similarly, try "inflation" instead of "pressure".

Searching by tire size may help, as may adding "PSI" or "KPa"

Sometimes an image search returns better results.

I'll bet the old Sears catalogs had the information.