ok i was wondering why i cant upgrade my car that i just bought i started on muscle car tier 1 now i bought the ford mustang wich is muscle car tier 2 and it wont let me upgrade the performance on the mustang why is that
Thats because you have no tier 2 parts. Here's a chart to show you how the part system works:
Tier 1 parts - Tier 1 Cars
Tier 2 parts - Tier 2 Cars
Tier 3 parts - Tier 3 Cars
Of course you know that the order of preformance from worst to best is Tier 1, Tier 2 then Tier 3 but you unlock the cars in pretty much the same way (except when you start in Angie's 21st Street). If your still confused PM me and tell me what you don't get.