If you like BackTrack then I could also recommend Classic Speedway Magazine too. It covers the early years of Speedway up until the start of the BackTrack era.
If you are looking for a Magazine that covers up to date Speedway - the only ones I know of are Speedway Star which you already get, and Inside Speedway the Magazine that has let you down.
Oohhh for good old days of Speedway Express.