all 1/8 scale tires and rims are a standard size, even the hex (thank christ!). so yes, knuckles 2.0 will fit on your stock rims. You said the track was hard clay with loose sand over the top, does the sand stay on the track at all times? if is gets swept off, you could try panther switch tires, those work really well on clay tracks. But the knuckles are a very good choice, especially if the clay is hard and dry like concrete.