Pictures shown below - started with a base covering soil with grass or in this case black fabric. This is I hope to prevent wireworms from coming out of the soil into the tires. The put down a tire (pick them up from gas stations or recycle centre for free!), then add soil to fill just over half of the tire. Place four seed potatoes (certified if you live in PEI), and then cover to the top with remaining soil. I then covered with buckwheat again to the hopes to deter wireworms. In another few weeks I'll plant a bean plant in the centre of the tire to deter potato beetles (usually I surround my potatoes with beans and this works very well.)
As the potatoes grow I'll add tire with dirt, when the potato plant goes higher I'll do the same again. I think I'll probably get 4 or 5 tires. I'll post again later.
Update July 4th, 2016 - I've topped up the potatoes with soil and in another week or so will add the second tire. I've also picked 4 potato tires to use straw instead of soil to top them up to see if they grow the same. There were zero potato beetles on the plants.