I'm looking at three different routes I could go on wheel size, and just want some opinions from the community to help my decision:

Option 1: 17x9.5 front / 18x10.5 rear
(Car is already running 17" Centerlines with 315 rubber on the back without issues, so I'm hoping the original Z06-size fits in there right. Not sure exactly what my current wheel width and offset are b/c I'm the second owner.)

Option 2: 18x9.5 front and rear

Option 3: 17x9.5 front and rear

These are obviously listed from the more exotic to the boring. I'm shopping AFS and OE Wheel Distributors. Which size option would you go with in my shoes, and why? Thanks

 

I don't like staggered sizes on the F-Body...I'd go with the 18x9.5's all the way around...or you could do 18x10's in the rear.

 

The factory C5 Z06 17x9.5" wheels have a 54mm offset. That works fine on a 4th Gen. The 18x10.5" wheels have a 58mm offset, giving them an ~8.0" backspace. That is going to produce the same issues as the 17x11" 50mm (7.93" backspace) wheels discussed in the FAQ.

Those are the factory specs. If you go aftermarket, they may offer different offsets, so you have to check with the manufacturer.

 

Going off info in the FAQ, it looks like I'd have a 25.5" tire height with either of the 18" widths versus 25.7" from the factory. What mph difference on the speedometer would that create?

Another difference I'd be interested to see is the weight difference. How much of an effect am I going to see with an 18x9.5 versus a 17x9.5?

Starting to think 17x9.5 on all four corners might be the way to go...

 

Appears your car left the factory with 245/50-16's. That would be a 25.65" tire. A 275/35-18 is a 25.58" tire. The difference would be about 1/4 of a percent, and the error at 60.0 MPH would be speedo reading 60.16 MPH. That's all "theory", using a formula to calculate the diameter of each tire from the size specifications. In fact, the dimensions shown in a tire size are "nominal", not exact. Actual tire dimensions are set by the manufacturer, and are "close". To compare the effects of two different tires, you actually have to pick the specific model and size tire you are considering, and see what the manufaturer rates the diameter at. A more accurate way to compare the impact on the speedometer is to use the manufacturer rated "revs/mile" for the specific tire you are looking at.

Using the numerical analysis on the 315/30-18, the error would be about 0.8%, and the speedo would be reagins 60.5 MPH at a true 60 MPH.

In a practical sense, its not worth worrying about. If you are concerned, its very easy to change the tire diameter in the PCM.

You can't go strictly by weight. The inertial impact (the HP absorbed in accelerating the wheel/tire) also has to include an evaluation of the location of the weight relative to the axle. The larger diameter wheel moves the centroid of mass farther from the axle, increasing the HP absorbed. Again, its not really all that significant when considering small changes.