driving capabilities with a wider rear?

[DJexor]

Can somebody tell me what will happen to the driving capabilities of a hachi when you widen up your rear. In the near future I will have to let my rear fenders restored and don't know what to do yet.

I have some 15 x 8,5J offset -21 wheels laying in my room and the ones mounted right now are 15 x 8J offset -2. I like the driving capabilities of my current setup, but will it change drasticly if I mount those wider wheels when I choose wider fenders? The lower offset and wider wheels will increase the trackwidth 5 cm in total. I will mount the same tires on it so that wont make the difference. I want to keep the front as same as it is now, but what will happen when the rear is extended like this??