It might be a heavy year for acorns in your area. The acorn crop can vary quite a bit from year to year. My city's nickname is the City of Oaks, and we have a lot of them. They are a little bothersome to ride through but I haven't felt in any danger of spilling as a result of hitting one. Personally, I detest sweetgum balls even more and wouldn't be surprised if they can cause flats.