Lets see....
I spent 100$ total for two 250lb weights or I could have spend about 800$ for 180lbs of weight on each tire, 3 metal weights of 60lbs each is the manufacturers recommendation,
If it breaks and falls off not losing much or damaging anything out in a field. Tires are not filled.
The eye bolts were only to pull it out of the form and to giggle it to get the bolts into the rim,
It has three grade 5 bolts that are 12 inches into the concrete, these bolts cross through the triangle of metal strapping to keep them straight during the pouring process and prevent them from pulling out, I also added a few ounces of fiberglass to the mixture.
Each bolt is good for over 3 tons so they are not the weak link considering it is only holding 250lbs that is fitting snug against the rim, this is why I used the tire rim itself as the form.
I have a few hours driving it so far, tightening/testing every 10 minutes, after the first 20 minutes slack on the bolts stopped appearing, the bolts are listed as good for 70lbs of torque, I will probably settle for 40 so not to stress the concrete any more than needed. I was hoping for personal experience with the torque question but this seems to be an unusual project so I suspect not much out there.
I have been on a variety of boards for decades, it is always a pleasure to get lots of opinions, is much better than silence, even when its grumpy old men similar to me.