hi guys....kind of new here..........what exactly is causing the extra weight?
the run flat tires alone? or the mini original wheels? or both?

if so, how much weights are we talking about?

 

Both. Check the wheels & tire forum - there's a thread there with weights for all of the factory wheel/tire offerings

 

My 205/45-17 Badyear all-season runflats on "S-lite" 17x7" rims weighed 49 lb apiece. My 205/45-16 Falken Azenis on 16x6.5" Enkei RPO1's weighed 37 lb apiece. That's a 48 lb difference in unsprung, rotating mass. That's huge in the effect on performance and feel.