For tire-diameter data - and also for load ratings - I recommend the Pep Boys web site, www.pepboys.com

On the left-side menu bar, use "Tires and Wheels", then pick a category and a tire model. Hunt around in the models till you find all the data you need.

Apparently both diameter and load capacity stay constant for any given tire size, pretty much regardless of tire model or manufacturer. I suspect the max air pressure will influence the specs if you compare tires with a 35 psi maximum with tires having a 44 or higher psi maximum (if you actually use them at those different presures). But if you compare apples to apples I think you can count on those specs to hold for same-size tires from other sources.