Not sure if that was to me or not, but here goes about 2 cents worth of " free advice":
I.M.H.O., Much like my "Georgia Adobe's" (TM) , "Earthship's" (TM) are just a "marketing trademark"
of a particular company, that describes their quality of work or products & perhaps appearance too, but not a particular building or materials use only.
Tires are just "free forms" and not for clay holding.
Clay is a free base material, that comes with many pieces of land, and just like Portland cement is, It's a binder, but not the single building material you will need.
Let's mentally Experiment a bit here , that would be the first methodology to most learning.
LOOK AT CLAY AND THEN AT PORTLAND CEMENT, UNDER YOUR OFFICE MICROSCOPE AND ONE WOULD SEE PLATELETS ! To me it always looks like the stack of dishes, that I once dropped into our kitchen floor - all broken up, but still flat or disk looking, yet all inter-tangled ,one upon the other, in places though .
Imagine making a brick, with just Portland cement (or go try to) it won't hold , as when it becomes dry it's brittle. Now add the 70% sand and mix well with water and you get a water stable brick.
Now, try that with clay, straw & sand & you have a brick, that's stable when dry, yet not water resistant. Even inside a free forming device like a tire, its just soft clay & not a complete building material with the structural ability required to build with. Now some will say ~ as you alluded to, "what about potters clay" ? While a fine product for many things, Its another device, with other properties than load bearing construction in mind. And, yet strong, it's not a complete building material, until vitrified ( burning & baking together those silica sands & clay into a pot or vase) , and even that sometimes breaks into many pieces , if not done correctly. If one were to bake a brick with this mix, the straw will allow a chimney effect, during firing and there are many tutorials on that subject.
At the end of my personal experiments, I find that ( like the old saying goes "parts is parts" ) I like to use the right stuff, so as get the best results.
I hope some of that was useful to you and ~ Y'all be safe building out there !.
Best Regards,
Joe Woodall , Rogue Eco-Architect
Georgia Adobe (TM)
Commerce, GA
http://www.georgiaadobe.com