As my friends in Texas say “the truth as it was told to me” is yes. As a kart steward when the MG’s became the “spec” tire, I inquired about grandfathering the Bridgestones for a year and was told no. I have heard of some regions not enforcing this – you might ask your local kart steward, but I was told it could affect insurance for the event….
Two suggestions. If you have to buy new, just buy the cadet tire – taller and thinner, but they will last forever – out local kid kart has been running on a set for many years. Option 2 – MG’s are the tire of choice for our local kart track – good used takeoffs are usually available for a song. In FJC it’s more about learning to drive, the tires aren’t a huge issue starting out.