1 set should last at least a couple of race days if not longer (I'm thinking a lot longer...maybe 6+ race days). Since we really haven't been running them yet it is really hard to say for sure. The thing to consider though is how tire wear changes the ride heights on the car which can change its handling characteristics. That is why in 1/12th I run at least 2 sets of tires and usually have 4 sets (1 for each run). In WGT running only 1 set of tires you will probably want to adjust ride height every other run. The set I have for the spare car should be competitive if the setup works. Foam tires can get a bit chunked on the edges and still work just fine. I think Dave brought a few sets in way back when we were trying to get the class started in front of Sandy Flemings when we raced there...but I don't know if he still has any left over.