Trying to achieve spacer effect (Fr:11mm/R:15mm) with wheels -am I calculating correctly?

This is my first post (and first Ferrari). I've been super happy w/ my 2010 Cali (albeit stupid sensor/computer headaches with it). I scour these forums all the time, but contribute very little, since I'm such a newbie w/ very little knowledge. I have been really liking the how most seem to have lowered w/ H&Rs and adding the Hill Engineering Spacers 11mm/15mm.

I finally found H&R springs from a performance shop in Germany (Can't find H&R lowering springs anywhere!) and got them installed yesterday. I love the way the car looks lowered! I think it's 1.37inches (35mm according to H&R). Now I need to work on its stance. Being that I like the look of the 11mm/15mm spacers, I'm trying to get wheels w/ the right offset (given that rim width is different) to achieve that same effect.
I've always liked Bronze wheels, and I found a set that might work. However, I need some help w/ the calculation (and help confirming clearance for fender and suspension).

According to what I've found: 2010 Ferrari California stock wheels are 5X114.3
Front: 8Jx20 ET44
Rear: 10Jx20 ET52.

Potential wheels:20" Verde Axis V99 Wheels Gloss Bronze -
Fr: 20X9 +38mm
R: 20x10.5 +45mm

For the fronts, 20x9 adds an extra 1" width, which means +0.5" (12.7mm) outward toward fender and 0.5" (12.7mm) inward toward suspension. With +38mm offset (from +44mm stock), that will push it additional 6mm.
So the rim will be 18.7mm out toward the fender, and rim will be 6.7mm closer to suspension (12.7mm - 6mm).
I'm assuming that 6.7mm closer to suspension won't be much of an issue, but I'll definitely have clearance issues w/ 18.7mm toward fender (ie: 18.7mm spacer - I've heard folks say 17mm is too much).
So for the front, I'd pretty much need a custom 44mm offset, which will acheive 12.7mm spacer effect due to 9" width. 45mm or more offset, I would have brake clearance issues?

For the rears, there is an extra 0.5" width. If I divide that in half, that means would push the rim out .25" (6.35mm) and the +7mm offset difference giving me about 13.35mm offset equivalent?? I'd be fine with that, but if I could get a custom 43 or 42mm offset in the 20X10.5 that should put me to about 15mm spacer equivalent?

Thanks for any input!

Jeff

 

Thanks for your reply! Yes, I'm going more for esthetics and the goal is to achieve the stance equivalent of 11mm Front and 15mm Rear spacers, using rims. I rarely push the car to it's limits, and I do not have any competitive events w/ the car, so precision and balance are secondary on my list (where esthetics is primary).
98% of my driving is street driving, where I probably only test the car to 50% of it's limits. I also am not a huge fan of large wheels,hence my choice to stay w/ 20" wheels.

So it seems like my thinking/calculations is correct:
- If width of rim is increased by 1 inch, then it is 0.5inch (12.7mm) outward, and 0.5inch inward. Hence, without any offset change, a 1 - inch increase in rim width is equivalent to a 12.7mm spacer?
- The difference in offset is the equivalent to spacer size (numeric value)?
- As long as the offset number is less than stock offset (more aggressive), I should be ok w/ brake caliper clearance?

What is the largest spacer people have used (and had no clearance issues) in combo w/ H&R 11mm/15mm spacers for a California?