Brainstorm needed from wide wheel experts
 

Okay, so on my Boxster, I'm going to be running 17x10" and 17x12" CCW Classics (yes it's flared) and I'm trying to double check my logic in regard to the offsets needed. The car will have aftermarket coil-overs, and I would rather error on the side of slightly too much offset and "fine-tune" the fit away from the shocks with spacers. I have talked to John at CCW and his estimation was +32mm in the front, and +19mm in the rear. After crunching some numbers, I think these figures are pretty darn close but I wanted to check with the "masses" just to get a third opinion before I order.

Not enough information to make a calculation . What are the offsets on these wheels ?
When you say flared, what exactly are you referring to ? I hope more than just rolling the fender lip . It seems strange that anyone would manufacture a 17 inch wheel as wide as 10 and 12 inches .

Did you even read my post? I don't have wheels, I'm having wheels made. The offsets will be whatever I want. I'm using 17" wheels because I don't need a larger wheel for brake clearance and I want as little weight as possible. This is a race car, not a street car. The body is literally flared meaning custom fiberglass panels.

This is the car in question. 986forum.com/forums/showthread.php?t=25697&highlight=subaru+conversion

You state in your post that you will be "running 17x10" and 17x12" CCW Classics", nowhere do you mention that they're being made to order with selectable offsets . Therefore, the presumption is that these wheels have already been produced. With that said, I can't imagine being able to clear the perch on a set of aftermarket of coilovers with anything greater than a + 10 or 11 et on a rear wheel that wide, and +31 or so up front .

I guess I just assumed that it was common knowledge to "wheel guys" that CCW makes custom wheels and that the Classics are especially "made to order". Also, my post was not really a "will these fit" post as much as a "what will fit" post.

Anyway, you may be right about the spring clearance, but its a lot easier to add 10mm of spacer than have the wheels remade to go the other direction.

To put things into perspective, I run the following "aggressive" setup on my boxster .

Fronts : 19x8 +31 et with 235/35/19
Rears: 19x10 +31 with 275/30/19

* there's roughly 10 mm's or so of clearance from the adjustable perch all around.

So if I use your set-up as a comparison, if I add 2 more inches of width overall to the wheel, I would have to subtract roughly 25mm offset to keep the same clearance on the springs which would put it at +6mm (maybe +10mm if I want to run a bit closer to the springs) on the rear. The way I would like to do it is to go conservative on the outside clearance and space the wheels away from the springs if needed. This is why I thought +19mm would be acceptable because IMO, a 5mm - 15mm spacer is completely acceptable with longer studs. On the front, I already know the stock Boxster 17x8.5 rears with +50mm will barely fit in the front and clear aftermarket coilovers so I know a theoretical +31mm should work with the 10" wide wheels.

Thoughts?

Seems plausible . A +50 et up front with an 8.5 inch wheel will leave about 3mm's of clearance from the strut. So that's way too close IMO.

We do it all the time on the Boxster Spec cars on the PSS9's and 255 tires. Some guys add a 5mm spacer but some don't.