If you have any older chunked tires, keep them. Using a razor blade, cut a piece off of the donor tire slightly bigger than the missing chunk. Then, using shoo goo or fabric glue, press the chunk into place. Once the glue has dried, put it on a tire truer and re-round the edges and take a couple passes along the tire to get it to the exact shape you want.
1989 Mazda Rx7
greddy t04b, megasquirt ecu, PlX wideband, 12x28x3 fmic, 50mm hks clone wg, ssqv bov, Safc, ss oil lines, walbro fuel pump, tubo intake manifolds, ssac exhaust manifold, 3" dp, 550cc primary/720cc secondary injectors, etc.