Reduce Understeer C4

[Newsboy]

I've purchased a set of 17" (55 offset) 7" & 9" wheels for my C4. I'm getting 255/40/R17's for the rear. I was thinking of getting 205/50/R17"s for the front.
To decrease understeer, would it be better to go with 215" in the front. If so, would these be 215/40's to maintain the aspect ratio?
Thanks

[Newsboy]

Sorrry, I meant 215/50/R17's in the front.

[ValveFloat]

Why not a 225/45/17 up front? 225F - 255R seems to be a popular combo on these cars.