luftgekuhlt
Does anyone have a suggestion for the backspacing for 18x7.5 front and 18x8 rear.
Will be running Porsche bolt pattern disc brakes and fat fenders.http://www.tirerack.com/wheels/DisplayWheel.jsp?wheelMake=Mille+Miglia&wheelModel=Spider+II&wheelFinish=Bright+Silver+Paint
Sometimes to move forward you must first fall backwards
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Marc

How fat? If you expect to be able to steer without any fender clearance issues (I'm assuming you'll be at something lower-than-stock for front ride height) you'll find that 7½" can be a tight squeeze. I'm setting up my bug for 6x16" fronts with CCC ~3"-wider fenders and it looks like it'll be reasonably comfortable, but I can't see getting an extra 1½" in there without making some compromises.

In the rear I've gotten 7x16" under stock fenders but had to trim a little bit off of the suspension bumpstop on the chassis and shorten one of the springplate bolt heads for sidewall clearance; on this car I'll be using 1½"-wider fenders and 25mm spacers instead. With fenders that wide 8" rims should be no problem in the rear with the right backspace/spacer setup.

My son has all of the offset/backspace figures written down for the various combinations we've tried, I'll get back to you with the particulars.
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Marc
Let's assume you have a balljoint front end and IRS rear.

Here's an IRS bug with1¼"-wider-than-stock rear fenders (CCC) with 1" (25.4mm) spacers and 8x16 rims with 52.3mm offset. Tires are 225/50-16. This car has Type III rear brakes which increase the track by ~8mm per side compared to bug brakes. The bumpstops had to be trimmed a little for safe inner sidewall clearance; with bug brakes you might have to reverse one springplate bolt too.
http://i2.photobucket.com/albums/y15/jblackburn24/IMG_0325.jpg

Up front, 50mm offset 16x6" rims (205/55-16 tires) with CBPerformance disc-brake drop spindles and 8mm spacers still limit the turning radius a bit (down from 2-3/4 turns lock-to-lock to about 2½ turns) unless the shock towers are trimmed and rewelded. 50-8=42mm - you'll need that as a maximum offset to be practical on the inside with 6" rims, which means 7½" rims would have to have 42-19=23mm offset. Whether that will provide adequate fender clearance depends upon the tire profile and how much you drop the front end.
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luftgekuhlt
Sorry for not getting back to it sooner was out of town for a wedding, and sorry for the lack of info.
The front fenders will be 3 inches wider and the rear will be 4 1/2 inches, and yes it is ball joint front and IRS rear, I'll be using Mark V Fiberglass fenders.
http://www.markvfiberglass.com/
And probably using CB performance 2 1/2 drop spindle brake kit part # 4177 up front and #4625 rear.
http://www.cbperformance.com/catalog.asp?ProductID=482
Sometimes to move forward you must first fall backwards
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