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I'm thinking you'd need tubbing. Doesn't the C6 wheel have different specs anyway?
 

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The C6Z06 wheels overall diameters and widths were not much different from a C5.

Rear 325/30-19 is 102% of a C5's 295. 26.68" vs. 26.13"
Front 275/30-18 is 96.6% of a C5's 265. 24.5" vs. 25.35"

The rear tire is only about 1/4" larger radius. There's no question it'll work.

These tires will fit. The bigger issue is the stagger. The C6Z06 front/rear diameters are almost 5.5% different from the C5Z06. This difference will cause problems with the C5's AH and TC systems and there is no way (currently known to me, at least) to reprogram these computers to compensate. Also, wheel offset may be a problem since the C6's suspension geometry is revised somewhat.

Even if you went to a 285/30-18 on the front, the stagger is too much. You need to go all the way up to a 315/30-18 on the front before you get down below a 2% delta, and a 315/30-18 up front is a tight (perhaps too tight) fit.
 

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I personally don't think they'll be a problem. I do know that the tires are not yet available. If you look at the aftermarket wheels/tires being run now, they're very similar to the C6Z package. I have 19" wheels with 305/30-19 rears...the 325/30-19 is very close in diameter. From what I understand, it's not the difference between the C5Z-C6Z wheel sizes that affect AH/ABS/TC but the % difference between the front/rear of whatever package you're running.
 

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Right. The front and rear tires are different diameters. This means they turn a different RPMs for the same road speed. The AH and TC need to know how fast each wheel is rolling (a measure of the tire's road speed) in order to determine if a tire is losing or has lost traction. To compute road speed, the computer uses a numerical constant to "normalize" the two different RPM/speed measurements. We don't care how it actually does this, we only care that we know that it "knows" there is a difference between the diameters and it is compensating. We know the stock tire diameters (for a C5Z06 this is rear 26.13" and front 25.35"). The diameter difference is 3.07%. If you go to the C6Z06 tire sizes, the ratio is 26.68/25.4 or about 5.04%. The difference, 5% vs 3%, or 2%, is how inaccurate the AH and TC computers will be in their estimates of wheel speed. The rear wheel is proportionally larger on the C6Z06 by most of that 2%. This means that the rear wheels turn slower for a given road speed than the computers think they do, by 2%. So it's the difference in the ratio between the front/rear tire diameters that matters.

Also, I did my math wrong in the previous post. 2% is close to the apparent limit of what's OK for a C5, plenty of people have run tire sizes with this delta and not had problems. If you could get a 285/30-18 up front instead of a 275/30-18, the delta would be well within the acceptable limit and the C6 rims would work just fine on a C5 (provided the offsets are OK).
 

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I doubt that a 325/30x19 will fit on the C5 on C6 Z06 wheels without modification (increased ride height, removal of brake duct tubbing or a combination).

- Wider tire
- Taller tire
- The offset & backspacing are different (greater). Even though the C6 Z06 has wider tires (295 vs 325) it has a narrower track.
- The C6 Z06 wheel is also wider, 12" vs. 10.5"

But nobody knows for sure because they are not available yet, wait a month or 2.
 
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