18x9.5 +58mm
18x10.5 +56mm

Are these offsets in need of spacers?

what is a good tire sizes?

I am currently running 275/40/R17 rear and 245/45/R17 in front on my Z06 C5 wheels.

 

on my 9.5's I am running 275s but I have 11's in the rear and I am running 315's so I would say like 305's

 

what offsets are your wheels?

would these require spacers?

 

The 18 x 9.5" 58mm in the front is going to be very close to the steering knuckle. That calculates out to a ~7.53" backspace. I run 7.42" and its tight, but my wheels are 17". The steering knuckle tilts inwards us it goes up, so with an 18" wheel you SHOULD be OK. Worse that could happen would be a 1/8" spacer. Fit them and see how close it is.

The 18 x 10.5" 56mm offset in the back is going to be very close to the inside fender. That's virtually the same backspace as my 17 x 11 50mm wheels, and I had to cut the projecting edge of the jounce bumper bracket, hammer the inner fenders slightly and recenter the chassis over the rear axle with an adjustable panhard rod. Again, try fitting them to the car and see what happens. Again, may need a 1/8" spacer if you don't want to hammer and cut. And, as noted in my writeup in the FAQ, there is a huge variation in the assembly tolerances at the rear of these cars, and some people have used the same wheels I have and indicate they did not have to do any of the things I did.

Front: 275/35-18 = 25.6" diameter or 285/35-18 = 25.9" diameter

Rear: 295/35-18 = 26.1" diameter or 305/35-18 = 26.4" diameter (but you will probably only find this size in "competition" tires, not legal street tires).

 

I have 4 stock C5 ZO6 17s (2 set of fronts) and I had to massage the inner fenderwells and they have been there for years now

ZO6 C5 Fronts (I have 4 of these)
Wheel size: 17 x 9.5
Offset: +54mm
Tire Size: 265/40/17
Back Spacing: 7.38” (187.35mm)

 

The 54mm offset gives you 0.16" less backspace than the 58mm offset wheels he will be using in the front. That's why he needs to fit them and check for interference.

As noted also, what fits on one 4th Gen may not fit the same on another. My 17 x 9.5" front wheels are 56mm offset, with 275/40-17 (25.7") and they did not require any fender massage. Surprised that you required hammering, since you are using an even smaller tire 265/40-17 = 25.3".

 

Ordered!
2pc 1 25" inch 5x4 75 to 5 x 4 75 Hubcentric Wheel Spacers 5LUG Adapters | eBay

275 40 R17 were in the rear prior (edit)

and the 18x10.5 are not even close, they hit bad! Fronts fit great. I know the Hubcentric/lugcentric thing, hipe they work great!

 

If you need a 1.25" adapter, the wheels can't possibly be 10.5" wide and 56mm offset. Something isn't right. With that width/offset, a 1.25" adapter will put the tires about 3/4" outside the fender.

 

hmmmm. I bought a 5/16in universal spacer and the wheel fit, but the studs were to short to use them. I figured since everyone in the C6 wheels thread said use 1.25 spacer that was what would get them flush.

I am going to measure and take a few pics of the wheel on the car, even thought its interfered with.

 

okay, I jacked up the rear end and kept the suspension loaded and installed the 18x10.5 wheel. It fits when the car is at ride level. Here are some pics. looks like its 58mm offset and 10.5 wide. The fronts are 56mm and 9.5 wide.

well with 3 hands the tape measure would be level, but I measure 1.5" to the edge of the fender.

 

here is my 97 with 50mm offset front and rear.

 

The factory C6 wheels, the one's shown in the C6 wheels on a 4th Gen "sticky", are 19 x 10.0" with a 79mm offset. That works out to a 8.6" backspace. They 1.25" spacer is larger than required to provide the clearance between the inside edge of the tire and the inner fender. 0.75" would provide the clearance. The additional 1/2" thickness moves the 10" wheel into the center of the wheel well, so it doesn't sit too deep in the well.

You need longer wheel studs if you are going to use a 5/16" spacer. That size spacer may move them far enough toward the outside to allow the outer edge of the tire to rub on the fender lip when the suspension compresses. I would think 1/8" spacer is all you need, but measure the clearance. You might have enough threads on the stud with 1/8". You need to have 12mm (a shade under 1/2") of threads engaged in the hex portion of the lug nut. The stud does not have to stick out of the end of the nut.

The reason they interfered with the suspension dropped when the car was jacked is the edge of the jounce bumper bracket hitting the rim/tire. That outer edge can be cut off. See my photos in the FAQ under the 17x11" wheel mounting post.

 

Okay, I ordered the longer ARP studs. Sent an email to the adapter person, hope they can cancel the order. I still think with the 5/16 spacers the wheels are going to still be tucked under the well, but test fit allows the wheel to fit at full droop.

 

I really like the flush look, not tucked way in, like all the 90s cars.

 

Bringing this back up. I am wondering if 1" spacers will fit on the back to flush these up. They are too tucked. that would make the offset of the 10.5 wheel +58 + 25mm= 83mm backspacing on a 10.5 wheel