Thinking of changing my 525I M-sport rim and the runflat tyres to M5 rim (19') with Michellin tyres. Wondering my type of car can take the type of rim, which are different size as compared with front and rear? My car is 2006 model. Btw, which tyres are best suited for my car if i take the 19" rim? Does the performance of the car will be worst of if i change from 18 inch to 19 inch... in my country, the 525I M-sport comes with 18 inch M-tech rim and runflat tyres.

Information had it that the runflat tyre is very bouncing and hard.... When negotiate the corner, the car swift....don't know whether it is true? Anyone has any experience on this.

 

The wheels will fit no problem. You will not get runflats in the tyre size you need for 19". So make sure you have the space saver wheel option or carry a can of tyreweld or similar.
The correct tyre sizes on the M5 wheel for your car are 245/35/19 front and 275/30/19 rear.
Although there should be a little performance theoretically, you won't notice much at all.

Good luck