calamari
ArboristSite Operative
If you don't want to mess with the tire and/or have wood that doesn't fit it, you can use a piece of light chain and a bungee cord. Put the round on end and wrap it tight with the bungee clipped into the end of the chain and then clip the other end into the chain to keep that tension. The chain gives you lots of adjustment for various diameters. Clip it above midway on the round so that the pieces won't fall over and out of the circle.
