I am looking into purchasing a new set of wheels and tires. What is the advantage of going to 18's on the front and back. Sticking with staggared.

 

I don't know about advantage but you'll have more options for tires when you need them. That's reallly the only reason I went with 18 & 19's.

 

If you are going to stick with staggered IMO I think I would do 18/19 and not 18/18.

Even more tires and sizes available.

 

18/18 is by far the superior choice. There is more tire options in 18 than any other size for our cars by far. The car was designed well before the 19 inch wheel took over and it's a smaller car that looks better with 18s than 19s. 18s ride nicer too and are less likely to be damaged by a pot hole or obstacles in the road. Did I mention 18s are cheaper for tires and wheels?

 

Any clearance issues up front going to 18's?

 

None whatsoever.

 

Exactly. There are way more sizes in 19" that will work on these cars, than 18's. Very little difference, if any, in price between 18" and 19" wheels, either.
Let's compare, from Tirerack.com and Discounttiredirect.com I limited 18" & 19" tire diameter to what is normally used on a street C5, between 25"-27"
Front tires:
255/35/18 (66)
255/30/19 (20)
255/35/19 (101)
265/35/18 (47)
265/30/19 (13)
265/35/19 (66)
275/35/18 (60)
275/30/19 (20)
275/35/19 (66)

Rear tires:
285/35/18 (21)
285/40/18 (4)
285/35/19 (54)
295/35/18 (9)
295/40/18 (3)
295/30/19 (21)
295/35/19 (12)
305/30/18 (0)
305/35/18 (2)
305/30/19 (32)
305/35/19 (3)
315/30/18 (7)
315/35/18 (0)
315/25/19 (2)
315/30/19 (1)
325/30/18 (0)
325/30/19 (17)

This is obviously not 100% of the tires in these sizes available but just what those two major tire suppliers list.

 

One thing to know, at least this was the case on my GTO, was going to 19's (vs 18's) reduced the number of wider tire options, because the overall size was more with 19's, even when trying to stay near the same size tires.

Otherwise yeah, I'd go for it, lots of tire options available and I'm assuming, just like the C6/C7, lots of wheel options already designed (not one-off) available. Contact vendor CW4L for wheel options

 

I went to 18/19 to take advantage of the tire "pairings" used for the C6. Better selection in general. Bought a set in C6 rim widths, and run tires in C6 sizes.

Personally, I think they look much better as well. 17/18's just look too small for the car these days, with everyone going the "big wheel" route on new cars.

 

I'm reposting this because it's a good question:
The issue for my application was, with 18's on my 1st GTO, I was able to run a 275/245 combo (sorry I don't remember the aspect ratio, but there are not a lot of options).

However, on my 2nd GTO the prev owner installed 19's, and had similar dia 275/245, but they rubbed on suspension compression! Both front and back - I had to downsize to 265/235 subsequently, and I had no rubbing issues as a result.

This was compounded by the fact that some lower aspect ratio tires on the 19's, was not load rated for the GTO. Better choice in this case was 18's, because of the overall dia of available tires combined with the load ratings.

Yes, this is vehicle dependent because of the wheel well space and turn radius, as well as suspension compression..

 

 

Go to tiresize.com and use the calculators and visualizers.

 

I just upgraded my z06 with two more rear 18x10.5 OEM speedline wheels. 285/35 ps4s all around and so far very happy with the setup. Fronts poke just a tad if you look really hard for it. I have never understood the front/rear diameter stagger (like an 18/19 or 17/18 setup). I am sure there is a reason, but I like the responsiveness of a true square setup and the ability to rotate the tires.

 

Here’s some of the reasons for the stagger from someone who knows: “a lot of track guys like the square set up but even the C5R, C6R, C7R actually used a staggered setup. In a street car, you disrupt the yaw sensing of the stability system so you lose some (a lot?) of your active handling because the car doesnt’ see the relative wheel spin difference. Bottom line, you are driving a street car, carefully designed to great performance but legal on the street with the necessary safety controls. If you screw around with that and say, have an accident, first thing an insurance company does is check the OBD II connector and see what you were doing. If you are not in a normal street mode (like being in Track mode) they can say you are at least partly to blame and deny a claim. Driving around with that setup and not being a track guy is like getting harnesses to look good but you are a poser. GM did a great job on the Corvette and there is very little an ordinary guy can do to improve, especially if he’s not an automotive engineer with access to all their testing data. “

 

Doubtful most insurance agents even know what a OBDII connector is let along that what cars come with selectable driving modes...

Depends on how you use the car.
Garage queen - go staggered since you would care more about looks than function. You typically won't push the car to the limit to feel the difference between square or staggered setup. rotating tires is a non issue since the car is not driven much.
Daily driver - go square setup to allow you to rotate tires to get the most life out of them. might find the limit in handling messing round on mountain roads etc. but the added front width is a benefit for handling. BTW I never use "competition mode". It's either normal driving mode or everything is OFF.
Daily/race toy - this is where I'm on the fence about square or staggered and if you have the same set of wheels/tires for both situations. But I may still lean toward a square setup for ability to rotate since racing/autocrossing will wear tires faster then DD.
Race toy - this is where every little bit helps so I may lean toward staggered to get the most out of the cars design.

OP, where do you fit into the above?

I 90% daily my car on all season Summitomo 285's on 18x10.5 square. I locally autocross on 315 square. Makes life easier when you have the same size wheels/tires.

 

Nice on the Summitomos, I ran through a few sets of 275's on the street with my 1st Goat!

I personally like the staggered setup, it works better for me and my intentions. I actually went down one width on the rear of my fresh C5Z to better balance the front, still used it as a drag radial on the street and I was just fine. Now, handling 9/10ths 10/10ths is another story, but I will have dedicated wheels and tires for the application.

 

Anyone know if running a 17x8.5 on front and 18x10.5 on back would be an issue? Can't think of any but just wondered.

 

You won't have any issue with that width.

 

I recommend reading this prior to selection. It really explains the whole wheel thing well. I went 19's all the way around and really like it.: http://www.toquez06.com/wheels.html

 

I thought Competitive Driving Mode was “all off”