That depends on a few things.....what compound.......how abrasive the track is and how hard you run the car .
The tire that most use is either a Hoosier sp-2 or a 15.....a 12 may be too soft depends on the track . Stay away from the sp-3 ..it's a rock....it will last a long time , but like I said it's a rock.
but normally about 4-5 good races ...that's an average .
Don't know what the American Racer compounds are but they have some that are comparable....
Best thing to do is talk to the guy's at the track that you are going to run at to get a better idea