So, have been planning to take my C5 on a road trip for the first time next week, about 500 miles round-trip to my sister's for Thanksgiving, and do not have run-flats, so for the off chance I have a tire issue, I got a tire slime compressor and sealant kit, and to cover all my bases, in case of catastrophic tire failure, I have gotten myself a spare tire setup for it.
I investigated the various space saver spare tire solutions, the 04-06 GTO $$$, the Modern Spare kit $$$$, and the one I decided to pursue was the 2010-2015 Chevy Equinox spare.
The Equinox spare looks basically identical to the GTO, although I do not know the exact dimensions and offsets of each, but they look the same.
One of the biggest differences is COST, the GTO spares I have found are running on the $150 to $200 shipped range, I picked this Equinox spare up for only $65 shipped, ebay had a 10% off coupon on it.
I had seen a lot of arguments on various forums about this setup not working for various reasons, the fact that this wheel has a 5x120mm bolt pattern instead of 5x120.65 (5x4-3/4)of the Corvette, and also that the Equinox uses 14mm lugs instead of the 12mm lugs the Corvette uses.
Neither of which has turned out to be any issue at all in fitting this spare tire setup to my car.
The ONLY modification to the Equinox wheel that was required to make it fit was to open the center hole to fit over the hub-centric wheel hub.
The Equinox wheel has a center bore of 66.9mm, the Corvette needs a 70.3mm center bore, so I had to grind and sand the opening up by 3.4mm.
Once that was done, the wheel fit right on and everything cleared.
The extremely slight difference in bolt pattern, 5x120 to 5x120.65, is so slight as to be insignificant. The difference of .65mm equals .0255 inches, and since that is on a circle, the difference in stud location is only .01275, basically within the margin of error, and the wheel bolted up to the studs with zero issue.
The other thing is the difference in lug hole size in the wheel between using a 12mm lug and a 14mm lug. And, for that I went on amazon and did some research and found a seller of lug nuts that has 12mm x1.5 lugs that used the larger body of some 14mm lugs, but with the 12mm threads, so the lugs fit the holes in the wheel just fine.

Now, the only other thing is the tire size.
The tire that comes on the Equinox spare is a 145/70R17 and it is a little short at 25.4", shorter than either the front or rear tire on the Corvette.
But, there is an alternative, a 145/80R17 made by Falken, and it is 26.5" tall, in between the front and rear tire diameters, it is rated at 2051 pounds and 81 MPH, and will work fine for a temporary spare and is only $94 at discount tire.
Many have said that the ABS and the rear limited slip diff will suffer from the mismatch, and maybe you'll get a abs/traction control warning, but the car will still drive okay, and the differential is designed to allow different wheel speeds between the two sides, and so long as you are not on the throttle hard then it will be fine too.

The other concern many have had is how to secure the spare so that it doesn't slap your head in a crash, and I have an idea about that too, and plan to show that in the next chapter of this project.

My video...

 

So the center hole was the wrong size, the bolt pattern was wrong, the stud size was wrong and the tire size was wrong but it fit just fine?

 

That's cheaper than a C4 18" spare that might not have the correct center hole ID, https://sparetire.com/Chevrolet/Corvette/1990/.

 

Part 2 of the space saver spare video, securing the tire for transport.

 

Join AAA so they can flat bed you to a tire shop.

 

That's not always so convenient...
My friend had a belt tensioner fail on his Avalanche once, Friday afternoon before Labor Day.
They waited 2 hours for the truck before he noticed an O'reilly's not too far off the freeway.
Walked the 1/2 mile, bought new belts, tensioners, and a cheapo tool set.
Walked back, replaced the stuff, and drove away before the truck even showed.

As for going through all those steps to make a wheel that doesn't fit work...
I'd just spend the extra $100.

 

What extra steps???
If you are referring to the GTO wheel, the center bore on it is too small for the Corvette as well, so it takes the same kind of work to make it fit.
Plus, from what I have read, the GTO wheel needs a spacer for caliper clearance.
So, why would you spend $100 more for that?

 

I guess if you like sitting on the side of the road waiting for them to show up, go for it.
And, that is IF you have cell service where you have the failure, and IF it isn't after hours at some local tire shop, and IF the tire is repairable, or IF they have the right size tire to replace the failed one with.
And, I have roadside on my insurance, but I'd rather have the spare as well.

 

Gotta give you an A+ for MacGyver techniques but I'd still say for an extra few hundred bucks the Modernspare is the way to go. New tire (not one over 10 years old). Proper hub size. Wheel/tire height. Toolkit and jack and it shows up ready to install. Also, I'm not so sure those latches you fasten the ratchet strap to will remain secure in all but the most minor fender bender. I like your thinking tho' .

 

Well, I bought a new tire, in the proper size, which neither the GTO or Equinox spare comes with the proper size, so you would need to change it for either wheel, and it was only $80, which the new tire size is listed in the video. Oh, and it is the same outer diameter as the 18" tire on the high dollar modern spare kit.
And, as far as tie downs, you would face the same issue with the modern spare as someone like me does with the alternative OEM GM spare, and I think that anything short of a major crash, the tire will stay put.
And, for my made up spare kit, I have only about $200 in it compared to that modern spare kit that is like $489.
Now, if you have big brakes, then the modern spare kit will clear some of them, but for base C5 and C6 brakes, my Equinox setup clears with no issue, and for a lot less money.
And, I am just offering my alternative "tire failure on the road" solution, if you don't like it, don't trust it, have lots of extra money to throw around, then DON'T DO IT.

 

Unaware that the GTO rim needed to be opened up. If it needs a spacer anyway, that's a lot simpler operation on a lathe....
Unless you have a GIANT lathe!

 

OP, would appreciate it, if you could you provide a link to the seller of the 14mm lugs, with the 12mm threads.

 

Amazon link is in the video text description.

 

Here's the link to the lug nuts,
22 bucks now, was 15 when I bought them.

 

I did the 2011 caddy donut. good dia. trial fit had no problem with the lug nuts. finger tight then impact. watched very close when tightening the lug nuts to check for misalignment.center bore was about 3 minutes with a dremel. I have a scissor jack with a Lowes impact and some of the same tools you have. tie down is similar to yours. 65.00 delivered to my door for the donut. some of the cons with other methods for me are. plug, I have plugged my tires off and on for decades. not all plugs can be performed on the car. slime. talk to the people that change tires about that stuff. lighter compressor, I've seen holes in the side of the tire that you could not add air. that being said I also like the Modern spare but i'm too cheap to go that way.

 

All similar to my reasoning behind my spare tire project.
Got the new tire mounted on it this afternoon, will be heading out tomorrow for our family Thanksgiving get together, with less worry about a flat tire.
And, probably will, hopefully will, not need to try the spare out, but if I do then...

 

Successful road trip to Dallas for Thanksgiving, and, of course, zero need to break out the spare along the way.
Biggest disappointment was fuel economy.
With cruise set at 70, DIC showed 26.4, actual measured fuel economy was 25.6...