Gabe007

I currently have a staggered wheels on my car. But I hear that, the tires cannot be rotated...

Is there a speed/gas/reaction/comfort difference if the wheels are not staggered?

Gullwing

I am perfectly happy not rotating my tires. If it was harmful then cars would not be sold with staggerred wheels.
How bad do you want to rotate them?

Gabe007

I can't really tell the difference between the staggered 8.5 J x 18 H2 (front) and 9.5 J x 18 H2 (rear). If I was to use the same size tires, the manual says use 8.5 J x 18 H2. I've seen a lot of people using 19+. I wonder if that voids factory/extended warranty (most likely not).

Anyway, if there is not much difference in performance then I rather go with same size tires so the tires can be rotated...

Gullwing

You would have some drop in performance and probably eat up the rears faster with smaller tires. The extra inch helps to get the power down.

The main benefit with the same size front and rear is with spare tires, but you don't have a full size spare so that doesn't matter.

Different size wheels/tires wont void the warranty, but it could cause ESP issues.