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Offset 56 mm.
Width 8.5" or 9.5"
Diameter 17" or more if you select lower profile on the tires to keep outer diameter correct.
Minor offset change is ok, but use your current wheels as reference.
10 mm less offset will push your rims out by 10 mm on each side.
Increasing width by 1 inch will ad 1/2 inch on inside and 1/2 inch on outside of rim.
Uhhhh, yes they are. They are definitely the stock base model wheel in 8.5/9.5 "staggered" widths.
Later-gen Corvette wheels have the same bolt pattern and hub bore, so they'll bolt up. They generally have more offset in the rear. You can work around this by using spacers to push them out to around the stock C4's net offset. The C8 wheels are a different bolt pattern and will not work properly.
Uhhhh, yes they are. They are definitely the stock base model wheel in 8.5/9.5 "staggered" widths.
Later-gen Corvette wheels have the same bolt pattern and hub bore, so they'll bolt up. They generally have more offset in the rear. You can work around this by using spacers to push them out to around the stock C4's net offset. The C8 wheels are a different bolt pattern and will not work properly.
Yes, you are right and I misread my own page made it many years ago.
1993-1996 base was a bit up from the 1996 A-molds
Would 03 C5 wheels fit? The specs from what I found on them are ..
Front: 17 x 8.5 Tire size: P245/45ZR-17.
Rear: 18 x 9.5 Tire size: P275/40ZR-18.
Bolt pattern 5x4.75" (same as 5x120.65mm)
Front offset= +58mm, Back Spacing= 7.0" (177.8mm)
Rear offset= +65mm, Back Spacing= 7.5" (190.5mm)
Obviously, the size and the offset of the rear wheels is different from mine. Its not even close. My wheels are 8.5" fx 17" front and 9.5" x 17" rear. The offset on my stock wheels front and rear are both 56mm.
Would I just need to add spacers to the rear and with spacers that large needed would I need to change the wheel studs to a longer size?
I am from Europe so I use metrics.
8.5" = 8.5 x 25.4 = 216 mm ( Center at 108 mm )
9.5" = 8.5 x 25.4 = 241 mm ( Center at 121 mm )
C5 front wheels go out 108 - 58 = 50 mm from brake rotor
C4 front wheels go out 108 - 56 = 52 mm from brake rotor
C5 rear wheels go out 121 - 65 = 56 mm from brake rotor
C4 rear wheels go out 121 - 56 = 65 mm from brake rotor
So ... Front wheels almost identical, 2 mm in.
Rear would be between your stock front and rear wheels, closer to the front.
Would 03 C5 wheels fit? The specs from what I found on them are ..
Front: 17 x 8.5 Tire size: P245/45ZR-17.
Rear: 18 x 9.5 Tire size: P275/40ZR-18.
Bolt pattern 5x4.75" (same as 5x120.65mm)
Front offset= +58mm, Back Spacing= 7.0" (177.8mm)
Rear offset= +65mm, Back Spacing= 7.5" (190.5mm)
Obviously, the size and the offset of the rear wheels is different from mine. Its not even close. My wheels are 8.5" fx 17" front and 9.5" x 17" rear. The offset on my stock wheels front and rear are both 56mm.
Would I just need to add spacers to the rear and with spacers that large needed would I need to change the wheel studs to a longer size?
Easy part first: the front C5 wheels will work just fine as is. I would recommend 245/45/17 tires.
The rears will fit without spacers: the 88+ C4s will accommodate up to 8" backspacing . However, they will be "tucked inside" and look a little goofy. You wouldn't think only 9mm of "inset" would be a big difference visually, but it is. It's also not really ideal for cornering performance. So yes, if I were using those C5 wheels I would use 10mm spacers. And yes, I believe that would require studs that are 1/2" longer. They aren't super hard to replace - right now it's just a matter of being able to find them in stock anywhere. ARP should have the correct length, but a lot of their studs seem to be out of stock. For rear tires, 275/35/18 will be the perfect width for the 9.5" wheel and the outside diameter will perfectly match the 245/45/17 front tires.
made it many years ago. 
